U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen

Available online at www.sciencedirect.com

ScienceDirect Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx www.elsevier.com/locate/gca

U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen Xiao-Ying Gao a,⇑, Yong-Fei Zheng a, Xiao-Ping Xia b, Yi-Xiang Chen a a

CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China b State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China

Abstract Rutile U–Pb ages and trace elements were determined by the LA-(MC)-ICPMS technique for ultrahigh-pressure (UHP) metamorphic quartzite from the Sulu orogen. The results provide insights into the effect of metamorphic fluid on element transport in the continental subduction factory. Rutile U–Pb dating yields a concordant age of 205 ± 2 Ma, whereas U–Pb dating of coexisting zircon gives two groups of concordant ages at 243 ± 4 and 223 ± 3 Ma, respectively. The Zr-in-rutile thermometry yields temperatures of 600–640 °C, consistent with the closure temperatures of 600–650 °C for Pb diffusion in the rutile. Although the rutile U–Pb age is significantly younger the younger group of zircon U–Pb ages, the consistency in the two kinds of temperatures indicates that the rutile U–Pb age has dated its growth, a kind of rapid cooling during exhumation. Core–rim profile analyses across a large rutile grain (15 mm in diameter) yield remarkable trace element zoning, with much lower contents of HFSE such as Nb, Ta, Sb and W but significantly higher U contents in the core than in the rim. The variations in HFSE are ascribed to growth zoning rather than diffusion resetting. Thus, these rutile domains may have grown from different compositions of metamorphic fluid. The significant enrichment of HFSE in the rutile rim suggests its overgrowth from the fluid that is locally enriched in Nb, Ta, Sb and W and thus interpreted as the product of phase separation from a supercritical fluid into aqueous solution and hydrous melt during the exhumation. The rutile rim also exhibits a large variation in Nb/Ta ratios from 19.4 to 29.6 that are variably higher than those of the primitive mantle. This is attributed to the geochemical composition of metamorphic fluid due to breakdown of hydrous minerals such as phengite and biotite during the exhumation. Significant Nb/Ta variations occur in different rutile domains, suggesting that the composition of metamorphic fluid changes during the exhumation. As a consequence, the fluid released from the exhumation dehydration of UHP eclogite-facies rocks tend to exhibit suprachondritic Nb/Ta ratios, whereas subchondritic Nb/Ta rutile would result if its growth is associated with prograde eclogite-facies metamorphism during subduction. Ó 2014 Elsevier Ltd. All rights reserved.

1. INTRODUCTION Rutile (TiO2) is an accessory mineral that occurs in magmatic, sedimentary and metamorphic rocks. It is common ⇑ Corresponding author. Tel.: +86 551 63600093; fax: +86 551

63603554. E-mail address: [email protected] (X.-Y. Gao).

in many high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks in oceanic and continental subduction zones (e.g., Zack et al., 2002; Meinhold, 2010). The study of rutile from these metamorphic rocks can provide not only insights into the petrogenesis and chemical geodynamics of subduction zones, but also constraints on tectonothermal history and element transport in subduction zones (e.g., Saunders et al., 1980; Rudnick et al., 2000;

http://dx.doi.org/10.1016/j.gca.2014.04.032 0016-7037/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

2

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Xiao et al., 2006; Pfa¨nder et al., 2007, 2012; Schmidt et al., 2009; Zheng et al., 2011a; Ding et al., 2013). In particular, rutile in eclogites is assumed as a sink of high field strength elements (HFSE) during subduction-zone metamorphism. In doing so, the eclogites are considered as restites after metamorphic dehydration resulting in significant release of aqueous fluids depleted in HFSE during crustal subduction to subarc depths of 80–130 km. However, metamorphic rutile may have grown in different stages during subduction-zone metamorphism. Thus, it is critical to determine at which stage metamorphic rutile has grown during subduction-zone metamorphism. Uranium can substitute for Ti4+ in the crystalline structure of rutile due to the comparable ionic radius and charge between the two elements. Rutile can contain considerable U content up to >100 ppm, providing a potential target for U–Pb dating (e.g., Meinhold, 2010; Zack et al., 2011). In fact, rutile U–Pb dating has been successfully performed for more than two decades by different methods (e.g., Corfu and Andrews, 1986; Scha¨rer et al., 1986; Richards et al., 1988; Li et al., 2003, 2011; Zack et al., 2011; Schmitt and Zack, 2012; Bracciali et al., 2013; Xia et al., 2013). However, the interpretation of rutile U–Pb ages is not straightforward due to uncertainties in the closure temperature of Pb diffusion in rutile (e.g., Mezger et al., 1989; Cherniak, 2000; Vry and Baker, 2006; Kooijman et al., 2010; Li et al., 2011). This problem can be partly circumvented by using the Zr-in-rutile thermometer that was recently established by empirical and experimental studies (Zack et al., 2004; Watson et al., 2006; Ferry and Watson, 2007; Tomkins et al., 2007). This thermometer has been widely applied to constrain the metamorphic conditions of highgrade metamorphic rocks (e.g., Spear et al., 2006; Baldwin et al., 2007; Miller et al., 2007; Chen and Li, 2008; Zhang et al., 2009; Zheng et al., 2011a; Kooijman et al., 2012; Ewing et al., 2013). As rutile can grow in various stages of subduction-zone metamorphism, linking U–Pb ages, trace element concentrations and Zr-in-rutile temperatures is a key to deciphering the growth history of rutile crystals. Rutile is a major carrier of HFSE in subduction-zone systems. It can accommodate a wide range of highly valent trace elements such as V, Cr, Fe, Al, Nb, Sn, Sb, Ta and W up to weight-percent level (e.g., Graham and Morris, 1973; Haggerty, 1991; Deer et al., 1992; Smith, 1997; Rice et al., 1998; Zack et al., 2002). Rutile has attracted considerable attention in deciphering the budget and mobility of HFSE, especially Nb and Ta, in subduction-zone systems (e.g., Green, 1995; Stalder et al., 1998; Rudnick et al., 2000; Foley et al., 2002; Klemme et al., 2002; Xiao et al., 2006; Ding et al., 2013; Marschall et al., 2013; Stepanov and Hermann, 2013). Rutile Nb/Ta ratios have been used as a geochemical fingerprint of geological processes such as the crust-mantle differentiation through subduction-zone metamorphism (Ding et al., 2009; Meinhold, 2010). Because all the known crustal and mantle reservoirs have primarily subchondritic Nb/Ta ratios, the terrestrial Nb–Ta paradox remains unresolved (e.g., Green, 1995; Foley et al., 2000; Rudnick et al., 2000; Kalfoun et al., 2002; Zack et al., 2002; Xiao et al., 2006; Miller et al.,

2007; Aulbach et al., 2008; Bromiley and Redfern, 2008; Ding et al., 2009; Schmidt et al., 2009; Meinhold, 2010). Several hypotheses have been proposed as the possible reservoirs with suprachondritic Nb/Ta ratios to solve this imbalance, including: (1) the storage of the “missing Nb” either in the metallic core (Wade and Wood, 2001; Mu¨nker et al., 2003) or in metasomatic domains of subcontinental lithospheric mantle (Aulbach et al., 2008; Pfa¨nder et al., 2012), and (2) the hidden reservoirs of either subducted eclogite or early enriched crust in the deep mantle with suprachondritic Nb/Ta ratios (e.g., McDonough, 1991; Kamber and Collerson, 2000; Rudnick et al., 2000; Kamber et al., 2002; Nebel et al., 2010). To ultimately solve the Nb–Ta paradox, it is important to know the Nb–Ta mobility and fractionation during various high-T geological processes, especially when dehydration and anatexis occur during subduction-zone metamorphism. The Nb/Ta fractionation has been a subject of several studies on rutile from UHP metamorphic eclogites in the Dabie-Sulu orogenic belt (e.g., Xiao et al., 2006; Liang et al., 2009; Zheng et al., 2011a; Huang et al., 2012). Rutile widely occurs in Dabie-Sulu UHP metamorphic rocks (Wang et al., 1995; Cong, 1996). These rocks have been intensively studied in perspectives of petrology, mineralogy, geochemistry and geochronology (e.g., Ernst et al., 2007; Zheng, 2008; Liou et al., 2009). The P–T conditions of various metamorphic stages and the complete P–T–t path have been established from petrological and zirconological studies of the UHP eclogites (Zheng et al., 2009, 2011a; Gao et al., 2011; Liu and Liou, 2011). Much attention has been paid to fluid regime and its bearing on the element and isotope behaviors during continental subduction-zone metamorphism (Zheng et al., 2003; Zheng, 2009, 2012). These studies have laid a solid basis for deciphering the relationship between fluid property and element mobility during the processes in subduction factory. In this regard, U–Pb age, growth temperature and trace element partitioning can be obtained from both zircon and rutile to provide insights into the geochemistry of metamorphic fluid. This study deals with rutile from quartzite that is a rare lithology in HP to UHP metamorphic zones. It experienced UHP metamorphism along with surrounding granitic gneisses and eclogites in the Dabie-Sulu orogenic belt (e.g., Liou et al., 1997; Ferrando et al., 2005; Frezzotti et al., 2007; Liu and Liou, 2011; Chen et al., 2013a). Large rutile grains up to several centimeters occur in some UHP quartzites. We conduct a combined study of both U–Pb ages and trace elements in metamorphic rutile from an UHP quartzite from the Sulu orogen. The results are used to provide insights into the property of metamorphic fluid and thus constraints on the behavior of HFSE, especially Nb and Ta, during subduction-zone processes. In doing so, a combined study of both U–Pb ages and trace elements was also carried out for coexisting zircon from the same quartzite. The integration of these rutile and zircon analyses allow us to decipher the growth timing and conditions of accessory minerals from metamorphic fluid and the behavior of Nb/Ta fractionation during metamorphic dehydration at subduction zones.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

2. GEOLOGICAL SETTING AND SAMPLES The Dabie-Sulu orogenic belt in east-central China was formed by continental subduction of the South China Block beneath the North China Block in the Triassic (e.g., Wang et al., 1995; Cong, 1996; Liou et al., 1996; Li et al., 1999; Zheng et al., 2003, 2009). It contains one of the largest (>30,000 km2) and best-exposed UHP metamorphic terranes recognized so far on Earth (e.g., Carswell and Compagnoni, 2003; Ernst et al., 2007; Zheng et al., 2012). The Sulu orogen is its eastern part, with an offset of 500 km to the northeast relative to the Dabie orogen due to the anti-clockwise movement along the Tan-Lu fault. The Sulu orogen is bounded by the Jiashan-Xiangshui fault (JXF) on the south and the Wulian-Qingdao-Yantai fault (WQYF) on the north (Fig. 1), and segmented into a number

3

of slices by several faults (Xu et al., 2006). It is divided into HP and UHP metamorphic zones, which are unconformably overlain by Jurassic clastic strata and Cretaceous volcaniclastic cover, and intruded by Mesozoic granites (Zhang et al., 1995; Liu et al., 2004; Zhao and Zheng, 2009). The UHP metamorphic zone mostly consists of orthogneiss and paragneiss, with abundant layers and blocks of eclogite, garnet peridotite, amphibolite, quartzite and marble. The eclogite occurs mainly as blocks or lenses in the granitic orthogneiss, and is subordinately enclosed within the marble and peridotite. Coesite inclusions occur in garnet and zoisite from the eclogite (Hirajima et al., 1990; Zhang et al., 1995; Yao et al., 2000; Zhang et al., 2008) and in zircon from the gneisses (Ye et al., 2000; Liu and Liou, 2011), quartzite and eclogite (Liu et al., 2004; Liu and Liou, 2011), indicating these rocks underwent UHP metamorphism.

Fig. 1. Simplified geological map in the Donghai area of the southwestern Sulu orogen (modified after Liu et al., 2004). Lithological units: (1) quaternary; (2) tertiary basalt; (3) cretaceous basin; (4) cretaceous granite; (5) aegirine-bearing granitic gneiss; (6) amphibole-bearing granitic gneiss; (7) garnet-bearing granitic gneiss; (8) biotite-bearing granitic gneiss; (9) amphibole- and biotite-bearing granitic gneiss; (10) epidoteand biotite-bearing granitic gneiss; (11) metamorphic rocks of supracrustal origin, including paragneiss, kyanite- and jadeite-bearing quartzite, and marble; (12) eclogite and ultramafic rocks; (13) ductile shear zone or fault; (14) sample site. Abbreviations: CCSD-PP1, CCSDPP2, and CCSD-MH are the Chinese Continental Scientific Drilling (CCSD) pre-pilot holes 1 and 2 and main hole, respectively; NCB, North China Block; SCB, South China Block; WQYF, Wulian-Qingdao-Yantai fault; JXF, Jiashan-Xiangshui fault.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

4

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Many petrological studies have demonstrated that the metamorphic rocks in the Sulu orogen underwent UHP metamorphism at 750–850 °C and 3.0–4.5 GPa (e.g., Zhang et al., 2005, 2009; Xu et al., 2006). Occurrence of coesite as inclusions in zircon from the Sulu metamorphic rocks indicates the widespread UHP metamorphism due to continental deep subduction in east-central China (e.g., Ye et al., 2000; Zheng et al., 2003; Liu and Liou, 2011). Many geochronological studies, particularly zircon U–Pb dating by different techniques, have indicated that the UHP metamorphism occurred at 240–225 Ma, with duration of 15 ± 2 Myr in the coesite stability field (Zheng et al., 2009). The majority of UHP rocks have igneous protolith of bimodal composition, formed probably in a continental rift zone in the middle Neoproterozoic (Chen et al., 2007, 2014; Zheng et al., 2008). The present study focuses on UHP metamorphic quartzite at Qinglongshan in Donghai County, the southwestern Sulu orogen (Fig. 1). There are a variety of UHP metamorphic rocks at this locality (Hirajima et al., 1990; Enami et al., 1993; Zhang et al., 1994, 1995, 2000; Yang and Jahn, 2000). The Qinglongshan is located at 12 km east of Donghai County (Fig. 1). An 850-m-long E–W highway road cut traversed the southern hillside of Qinglongshan. Previous studies have examined the petrology, mineralogy, geochemistry and geochronology of UHP metamorphic rocks in this area (e.g., Zhang et al., 1995, 2005; Zheng et al., 1998; Chen et al., 2011, 2013a, 2013b). In terms of field occurrences, five rock types are recognized at Qinglongshan, including paragneiss, orthogneiss, eclogite, quartzite and schist. Coesite and its pseudomorph were observed in all of these rocks (Zhang et al., 1995, 2005; Liu et al., 2004; Liu and Liou, 2011; Chen et al., 2013a, 2013b), demonstrating that these rocks underwent UHP metamorphism at mantle depths of >80 km. Metamorphic minerals usually contain multiphase solid (MS) inclusions that primarily consist of more than one felsic mineral. The MS inclusions containing significant amounts of alkali-alumino-silicates also occur in UHP eclogite and kyanite quartzite at Hushan adjacent to Qinglongshan, which were interpreted as remnants of high-density supercritical fluids formed at peak UHP metamorphic conditions (Ferrando et al., 2005; Frezzotti et al., 2007). A sample of quartzite 09SL07 was selected for this study, which is hosted by the UHP granitic orthogneiss (Fig. 1). It was also taken from the southern hillside of Qinglongshan, close to quartzites used in the study of Chen et al. (2013a). Nevertheless, all these samples are apart from each other by tens to hundreds of meters. The quartzite used in the present study only contains few minerals like rutile, allanite and phengite. Kyanite and topaz are absent, unlike quartzites studied by Ferrando et al. (2005) and Frezzotti et al. (2007) from Hushan. Chen et al. (2013a) have found petrological evidence for anatexis of quartzite at Qinglongshan, including the feldspar grains exhibiting an elongated, highly cuspate shape or occurring as interstitial, cuspate phases constituting interconnected networks along grain boundaries of quartz crystals. In addition, some anatectic zircon domains (growing from anatectic melts) contain coesite inclusions, indicating that

the anatexis would have started at UHP conditions during the initial exhumation and continued at reduced pressures through HP eclogite-facies to even amphibolite-facies conditions (Chen et al., 2013a). 3. ANALYTICAL METHODS 3.1. Mineral major elements Major element analyses and backscattered electron (BSE) imaging of such minerals as phengite, epidote and allanite were performed by the wavelength dispersive method using a Shimazu EPMA 1600 electron microprobe (EMP) at CAS Key Laboratory of Crust-Mantle Materials and Environments in University of Science and Technology of China (USTC), Hefei. The working conditions were at 15 kV for accelerating voltage and 20 nA for beam current, with a beam diameter of 1 lm. Natural silicate standards were used, and the raw data were reduced using conventional ZAF correction procedures. The major element concentrations usually have analytical uncertainties < ± 5% (2r) based on the repeated analyses of mineral or glass standards. The mineral abbreviations through the text, including the figures and tables in this paper, are after Whitney and Evans (2010). 3.2. Zircon U–Pb dating and trace element analysis Zircon grains were separated from samples and extracted by crushing, sieving and heavy liquid methods, and then purified by hand picking under a binocular microscope. Representative zircon grains without cracks were mounted in epoxy for U–Pb dating and trace element analysis, and then polished down to expose grain centre. The CL images were obtained using an FEI Sirion 200 Scanning electron microscope (SEM) at USTC. The working conditions during the CL imaging were maintained at 20 kV and 15 nA. In-situ analyses of zircon trace elements and U–Pb isotopes were conducted by laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS) at State Key Laboratory of Geological Processes and Mineral Resources in China University of Geosciences (CUG), Wuhan. Detailed operating conditions for analytical protocols and data reduction have been described by Liu et al. (2008, 2010). An Agilent 7500a Q-ICPMS was connected to a GeoLas 2005 193 nm excimer ArF laser-ablation system. Helium was used as the carrier gas, and argon as the sample gas was mixed with the carrier gas via a T-connector before entering the ICP. Each analysis incorporated approximately 20–30 s background acquisition (gas blank) followed by 30–50 s data acquisition from the sample. The Agilent Chemstation was utilized for the acquisition of each analysis. Analyses of the zircons were conducted with a laser repetition rate of 6 Hz, the energy density of 60 mJ and beam diameter of 24 lm. Off-line selection, integration of background and analyte signals, time-drift correction and quantitative calibration for trace element analysis and U–Pb dating were performed by an EXCEL soft-ware ICPMSDataCal (Liu et al., 2008, 2010). The zircon standard 91500 was used as the external

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

standard for calibration, and analyzed twice every 5 analyses of unknowns. Time-dependent drifts of U–Th–Pb isotope ratios were corrected using a linear interpolation (with time) for every five analyses according to the variations of 91500. Preferred U–Pb isotope ratios used for zircon 91500 are from Wiedenbeck et al. (1995). Uncertainty of preferred values for the external standard 91500 was propagated to the ultimate results of samples. Zircon standard GJ-1 was analyzed as unknown sample to monitor the data quality. The obtained mean 206Pb/238U age for GJ-1 in this study is 603 ± 2 Ma (MSWD = 0.42, n = 21), consistent with the recommended value of 599.8 ± 1.7 Ma (Jackson et al., 2004). Concordia diagrams and weighted mean calculations were made using Isoplot/Ex_ver3 (Ludwig, 2003). The common Pb correction was performed by the EXCEL program ComPbCorr#3_151 (Andersen, 2002). Uncertainties of individual analyses are reported with 1r errors; weighted-mean ages were calculated at 95% confidence level. Trace element concentrations of zircon were calibrated using 29Si as an internal reference and NIST SRM 610 as an external reference material (Liu et al., 2010). The preferred values of element concentrations for the reference glass are from the GeoReM database (http://georem.mpch-mainz.gwdg.de/). The precision and accuracy of the analyses are better than ±10% (2r) for most trace elements based on the replicate analyses of the reference material (GJ-1). The Ti-in-zircon thermometer of Ferry and Watson (2007) was applied under the assumption that aTiO2 = 1 and aSiO2 = 1 during zircon growth. 3.3. Rutile trace element analysis The trace element analysis of rutile was performed on prepared thin sections by the LA-ICPMS method also at State Key Laboratory of Geological Processes and Mineral Resources in CUG, Wuhan. The detail of the operating conditions for the laser ablation system and the ICP-MS instrument and data reduction are the same as presented by Liu et al. (2008, 2010). Ablation spots were set to be 32 lm, with the laser energy of 65 mJ and a frequency of 6 Hz. The USGS glasses NIST610, BCR-2G, BHVO-2G and BIR-1G were used as the reference materials for multiple-standard calibration without an internal standard (Liu et al., 2008). Off-line selection and integration of background and analyte signals, and time-drift correction and quantitative calibration were conducted by ICPMSDataCal. Reproducibility and accuracy of trace element concentrations were assessed to be better than ±5% for major elements and better than ±5–10% for most trace elements based on the analysis of reference materials (BCR-2G, BHVO-2G and BIR-1G). To acquire reliable trace element concentrations, the time-resolved spectra of every element for every sample were carefully examined, especially the elements P, Th, Ca, Si and light rare earth elements (LREE), to exclude the inclusions of apatite, monazite and allanite in rutile. Analytical precision and accuracy for trace elements are the same as Liu et al. (2008). Zr-in-rutile temperatures were calculated using the pressure-dependent calibration of Tomkins et al. (2007) because

5

it has quantitatively optimized the temperature effect on the uptake of Zr-in-rutile at different pressures. In addition, the thermometer of Tomkins et al. (2007) was applied under the assumption that aZrSiO4 = 1 and aSiO2 = 1 during rutile growth. 3.4. Rutile U–Pb dating The U–Pb dating of rutile was performed by LA-MCICPMS on a Neptune Plus multi-collector ICPMS at State Key Laboratory of Isotope Geochemistry in Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou. Analytical procedures are closely following those described by Xia et al. (2013). The collector system has 17% relative mass range, allowing simultaneous acquisition of ion signals ranging from mass 202Hg to 238U, an important factor in obtaining highly precise and accurate U–Pb age determinations. With a standard concentric nebulizer and spray chamber, this instrument commonly gives a sensitivity of >1200 V for 1 ppm solution of 238U. The MC-ICPMS was equipped with an ArF excimer 193 nm Resolution M-50 (Resonetics LLC, USA), which has been described in detail by Mu¨ller et al. (2009). This system can wash out 99% signal in less than 1.5 s due to its innovative sample cell design. Helium gas, which carries the laser ablated sample aerosol from the sample cell, is mixed with argon carrier gas and nitrogen as additional di-atomic gas to enhance sensitivity, and finally flows into the MCICPMS torch. The typical operating conditions for this study include repetition rate of 5 Hz, crater size of 44 lm, and energy density (fluence) on target of 4 J/cm2. The samples were prepared as grain mounts. The mounts were well polished and thoroughly cleaned by polishing the surface with r-alumina powder, and then put in an ultrasonic bath for 5 min with milli-Q water, and finally dried with ethanol-soaked kimwipe paper. A polarizing microscope and BSE imaging were used to find crackand inclusion-free rutiles. Prior to analysis, gas flow rates of argon dominate the gas and, helium and nitrogen carrier gases were optimized to achieve the maximum sensitivity with low oxide production (238U16O/238U < 1%). The rutile was pre-ablated for five laser pulses to remove surface contamination before analysis. Each analysis incorporated a background acquisition of approximately 30 s (gas blank, closing the laser shutter) followed by 30–50 s data acquisition for the sample. Signals 208Pb, 207Pb, 206Pb, 204Pb (+204Hg) and 202Hg were measured on the ion counting channels, whereas signals 238U and 232Th were acquired on Faraday collectors. Corrections for instrumental drift, mass bias and elemental fractionation were all conducted by a ‘standard-sample-standard’ bracketing external standardization technique. One piece of standard rutile R19 (Luvizotto et al., 2009; Zack et al., 2011) with a size of 2  1  2 mm was used for calibration. It was analyzed twice every five analyses. This configuration cannot measure an element suitable for internal standardization, so no U and Pb concentration are given. Off-line data reduction (including selection and integration of background and analysis signals) was performed by an in-house created spreadsheet program. Because rutile

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

6

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

contains extremely low Th, correction to common lead was performed by estimating its content based on the 208Pb signal intensity assuming that all the measured 208Pb is nonradiogenic (Zack et al., 2011). The two-stage Pb evolution model of Stacey and Kramers (1975) was adopted for this purpose. Time-dependent drifts were corrected using a linear interpolation (with time) for every five analyses according to the variations of the standard rutile R19. In this study, 80 spot analytical dataset for the external standard R19 give a reproducibility of ±0.6% (1r) for 207Pb/206Pb and ±2.1% (1r) for 206Pb/238U. These uncertainties were propagated to the ultimate result of each sample analysis following Horstwood et al. (2003). In order to evaluate the accuracy of the result, another standard rutile R10 (Luvizotto et al., 2009) was analyzed. Twenty-three analytical spots yield a weighted mean age of 1089.4 ± 6.2 (2r) Ma, in agreement

with its recommended TIMS age of 1095 Ma (Luvizotto et al., 2009; Zack et al., 2011). 4. RESULTS 4.1. Petrology Sample 09SL07 is quartzite. It is primarily composed of quartz, with low fractions of accessory phases such as phengite, epidote, allanite and rutile that occur as large euhedral megacrysts (Fig. 2). Rutile grains do not show the presence of mineral inclusions. Ilmenite needles occur in the core and rim of rutile (Fig. 3b), some of them are related to cracks (Fig. 3). Relatively small zircon grains of <100 lm size were observed in thin sections. Highly cuspate, interstitial plagioclase grains occur along the quartz–quartz

Fig. 2. Photographs of rutile-bearing quartzite in the Sulu orogen. (a) The blocks of quartzite; (b) an oriented acicular rutile-bearing segregation in the quartzite. The coin in the photographs is 2.5 cm in diameter (cross-polarized light, XPL); (c) large cm-size phengite in association with quartz (plane-polarized light, PPL); (d) large cm-size allanite in association with quartz; (e) interstitial, highly cuspate plagioclase along quartz-quartz grain boundaries (XPL); (f) elongated, highly cuspate K-feldspar occurring along quartz–quartz grain boundaries or in quartz triple junctions (XPL).

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

grain boundaries with low dihedral angles (Fig. 2e). Elongated felsic veinlets composed of feldspar and quartz, several centimeters in length, occur along the quartz–quartz boundaries (Fig. 2f). They constitute the interconnected network along the grain boundaries and triple junctions. Some part of the quartzite was subjected to variable degrees of amphibolite-facies retrogression, which is indicated by replacement of allanite with a symplectitic corona of amphibole + albite (Fig. 2d). Most phengite grains are rimmed by retrograde black corona (Fig. 2c). Phengite megacrysts have relatively homogeneous compositions (Table 1), with high SiO2 contents of 53.8– 55.0 wt.% (Si = 3.57–3.66 pfu, O = 11), Al2O3 contents of 22.8–24.4 wt.%, K2O contents of 8.21–9.21 wt.% and MgO contents of 4.68–5.19 wt.%. The trace element composition of phengite megacrystals exhibits strong enrichment of LILE such as Rb (235–286 ppm), Ba (1319–2177 ppm), Sr (13.2–23.7 ppm) and Pb (6.3–18.6 ppm), but depletion of

7

REE. Notably, phengites show very low contents of Nb and Ta, mostly below detection limit (Table 2). Epidote occurs with a skeletal shape, and its interior is filled by quartz and plagioclase. Epidote from the quartzite exhibits homogeneous compositions in major elements such as SiO2 (38.0–38.2 wt.%), Al2O3 (23.5–23.8 wt.%), FeO (10.5–10.9 wt.%), CaO (22.3 wt.%) (Table 1). REE analyses of epidote yield steep MREE–HREE patterns with strong LREE enrichment and significantly positive Eu anomalies (Fig. 4) and high contents of Sr, Y and Pb (Table 2). Allanite in the core has relatively homogeneous contents of CaO (17.5–18.9 wt.%), Al2O3 (22.9–24.0 wt.%), FeO (7.03–7.93 wt.%) and SiO2 (33.8–34.9 wt.%). In addition, allanite in the rim exhibits variable contents of CaO (14.7–15.4 wt.%), Al2O3 (19.6–20.4 wt.%), FeO (6.55– 7.17 wt.%) and SiO2 (28.1–30.1 wt.%), with a total of less than 74 wt.%, indicating the presence of significant water and REE contents. Trace element analyses show high

Fig. 3. A rutile megacrystal from UHP metamorphic quartzite at Qinglongshan in the Sulu orogen. (a) Photomicrograph for the rutile megacrystal; (b) BSE images for exsolution of ilmenite needles in rutile core; (c) BSE images for exsolution of ilmenite needles in rutile rim. Also shown is the position of two profiles for the LA-ICPMS analyses of trace elements. The two profiles are denoted by A1–A33 and B1– B21, respectively.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

8

Mineral No.

Ph A-1-1

Ph A-1-2

Ph A-1-3

Ph A-1-4

Ph A-1-5

Ph A-1-6

Ph A-2-1

Ph A-2-2

Ph A-2-3

Ph A-2-4

Ph A-2-5

Ph A-2-6

Aln E-1-1

Aln E-1-2

Aln E-1-3

Aln E-1-4

Aln E-1-5

Aln E-1-6

Aln E-1-7

Aln E-1-8

Ep E-2-1

Ep E-2-2

SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr2O3 NiO F Total

54.97 0.26 22.80 2.07 – 5.16 – 0.03 8.36 0.02 0.01 0.18 93.85

54.82 0.31 23.79 2.08 – 5.15 – 0.11 8.30 0.05 0.07 0.17 94.84

54.89 0.31 23.51 1.90 – 4.94 – 0.04 8.59 0.04 – 0.14 94.36

53.83 0.44 24.04 2.23 – 5.19 – 0.02 8.58 – 0.06 0.27 94.66

55.00 0.30 23.99 1.95 – 5.07 – 0.10 9.21 0.07 0.04 0.20 95.93

54.90 0.47 23.18 2.17 0.01 5.19 – 0.07 8.55 – – 0.20 94.74

54.51 0.31 23.74 2.33 – 4.82 – 0.04 8.21 – 0.09 0.17 94.21

53.80 0.38 24.29 2.23 – 4.86 – 0.10 8.41 0.03 – 0.20 94.29

54.52 0.34 24.43 2.20 – 4.68 – 0.14 8.75 – – 0.17 95.22

55.04 0.38 24.09 2.20 0.09 5.09 – 0.05 8.62 0.05 – 0.25 95.86

54.62 0.37 23.49 2.16 0.02 5.10 – 0.06 8.46 0.07 0.14 0.19 94.68

54.89 0.38 23.87 2.33 0.07 5.07 – 0.09 8.44 – 0.02 0.19 95.33

34.09 0.09 22.92 7.93 – 0.69 18.91 nd nd 0.01 nd nd 84.64

34.93 0.06 23.48 7.47 – 0.61 18.88 nd nd 0.03 nd nd 85.45

34.43 0.06 23.95 7.20 – 0.71 17.85 nd nd 0.05 nd nd 84.25

34.40 0.07 23.57 7.03 – 0.76 17.88 nd nd 0.01 nd nd 83.71

34.58 0.09 23.34 7.17 0.01 0.75 17.88 nd nd 0.01 nd nd 83.81

33.81 0.09 23.22 7.23 – 0.78 17.47 nd nd – nd nd 82.59

30.14 0.11 20.38 6.55 – 0.70 15.38 nd nd 0.03 nd nd 73.29

28.05 0.14 19.59 7.17 – 0.66 14.74 nd nd 0.03 nd nd 70.38

38.22 0.21 23.52 10.89 0.16 0.10 22.31 0.02 – nd nd nd 95.41

38.04 0.22 23.75 10.54 0.17 0.11 22.34 0.02 – nd nd nd 95.19

O Si Al iv Al vi Ti Cr Fe2+ Fe3+ Mn Mg Ni Ca Na K F Total

11 3.66 0.35 1.44 0.01 – 0.12

11 3.61 0.39 1.46 0.02 – 0.12

11 3.63 0.37 1.46 0.02 – 0.11

11 3.57 0.43 1.45 0.02 – 0.12

11 3.60 0.40 1.45 0.02 – 0.11

11 3.63 0.38 1.43 0.02 – 0.12

11 3.61 0.39 1.47 0.02 – 0.13

11 3.57 0.43 1.47 0.02 – 0.12

11 3.59 0.42 1.48 0.02 – 0.12

11 3.60 0.40 1.45 0.02 – 0.12

11 3.61 0.39 1.44 0.02 – 0.12

11 3.60 0.40 1.45 0.02 – 0.13

12.5 3.04 2.41

12.5 3.08 2.44

12.5 3.06 2.51

12.5 3.08 2.49

12.5 3.09 2.46

12.5 3.07 2.48

12.5 3.08 2.46

12.5 3.00 2.47

12.5 3.06 2.28

12.5 3.05 2.25

0.01 –

– –

– –

0.01 –

0.01 –

0.01 –

0.01 –

0.01 –

0.01 –

0.01 –

– 0.51 – – – 0.71 0.04 6.83

– 0.51 – – 0.01 0.70 0.04 6.84

– 0.49 – – 0.01 0.73 0.03 6.83

– 0.51 – – – 0.73 0.06 6.89

– 0.50 – – 0.01 0.77 0.04 6.89

– 0.51 – – 0.01 0.72 0.04 6.86

– 0.48 0.01 – 0.01 0.69 0.04 6.83

– 0.48 – – 0.01 0.71 0.04 6.86

– 0.46 – – 0.02 0.73 0.04 6.86

0.01 0.50 – – 0.01 0.72 0.05 6.87

– 0.50 0.01 – 0.01 0.71 0.04 6.85

– 0.50 – – 0.01 0.71 0.04 6.85

0.59 – 0.09

0.55 – 0.08

0.54 – 0.09

0.53 – 0.10

0.54 – 0.10

0.55 – 0.11

0.56 – 0.11

0.64 – 0.11

0.73 0.01 0.01

0.71 0.01 0.01

1.81

1.78

1.70

1.71

1.71

1.70

1.69

1.69

1.91

1.92

7.95

7.93

7.91

7.91

7.91

7.91

7.90

7.93

7.95

7.96

Note: mineral abbreviations: Ph = phengite, Aln = Allanite; “nd”, not determined; “–”, below detection limit.

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

Table 1 Major element compositions of minerals from UHP quartzite at Qinglongshan in the Sulu orogen (wt.%).

Spot

Ph-4

Ph-6

Ph-7

Ph-8

Ph-9

Ph-10

Ph-11

Ph-12

Ph-13

Ph-15

Ph-16

Ph-17

Ph-18

Ep-5

Ep-6

Ep-7

Ep-8

Ep-10

Ep-11

Li Be P Sc V Cr Ni Ga Rb Sr Y Zr Nb Sn Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U

9.14 14.4 58.1 2.03 214 66.1 58.5 41.1 255 23.7 bdl bdl bdl 11.86 2177 0.140 bdl bdl bdl bdl bdl bdl bdl 0.221 0.132 0.381 0.092 bdl 0.133 0.340 bdl 14.0 bdl bdl

8.74 8.85 62.8 2.64 230 105 69.3 44.2 286 15.7 0.087 bdl 0.025 3.90 1541 bdl bdl 0.017 bdl 0.520 bdl bdl bdl 0.707 bdl 0.336 bdl 0.667 bdl 0.262 bdl 12.6 0.228 bdl

9.78 12.2 39.3 1.93 230 94.9 68.4 43.7 284 15.8 0.249 0.788 0.046 7.52 1518 bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 0.023 bdl bdl 11.2 0.127 0.023

9.52 11.0 66.7 2.00 231 106 74.2 42.4 286 14.5 bdl bdl 0.376 4.13 1496 bdl 0.072 bdl bdl bdl 0.278 bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 11.6 bdl 0.103

9.38 16.1 72.5 2.15 233 94.2 69.7 41.3 286 15.6 0.222 5.138 0.032 3.04 1513 bdl bdl bdl 0.207 0.393 bdl bdl bdl bdl bdl 0.059 bdl bdl 0.002 bdl bdl 10.7 0.041 0.151

9.29 10.9 60.9 2.62 232 88.0 74.7 44.0 282 13.2 bdl bdl 0.152 5.30 1442 bdl 0.191 0.223 bdl bdl 0.288 0.388 bdl bdl bdl bdl bdl 0.414 bdl bdl bdl 7.12 bdl 0.235

9.64 13.6 68.9 1.54 233 84.6 65.6 42.3 278 14.2 bdl 0.877 0.051 5.84 1416 bdl 0.236 bdl bdl bdl bdl bdl bdl bdl 0.0273 0.159 0.0102 0.0511 bdl 0.145 bdl 8.39 bdl bdl

9.19 11.2 59.5 2.34 231 87.3 68.0 45.1 275 14.0 0.580 0.000 0.319 6.45 1404 0.040 bdl bdl bdl 0.277 bdl bdl 0.167 bdl 0.167 0.475 bdl bdl 0.1025 0.186 bdl 8.47 bdl bdl

9.11 9.72 32.2 2.14 231 98.5 60.3 42.9 281 13.9 bdl bdl bdl 2.94 1397 bdl bdl 0.083 bdl bdl bdl bdl 0.0390 bdl bdl bdl 0.0339 0.159 bdl 0.071 bdl 8.06 bdl bdl

10.0 7.51 65.3 3.08 231 85.3 60.3 39.8 235 16.6 0.765 bdl 0.191 2.22 1319 8.76 1.41 1.55 6.13 0.568 bdl bdl 0.252 bdl 0.314 0.222 bdl 0.0742 bdl bdl bdl 11.2 bdl 0.0278

11.4 13.4 104 2.25 237 102 53.2 41.3 257 15.2 3.22 bdl 0.460 4.03 1496 8.78 1.30 1.62 11.6 bdl 0.760 bdl 0.0810 0.0374 bdl 0.696 0.0853 0.625 bdl bdl 0.021 18.6 0.206 0.302

10.2 10.8 64.6 2.69 223 45.2 59.8 40.4 273 23.0 0.048 0.305 0.390 13.16 2041 bdl bdl 0.194 bdl bdl bdl bdl bdl bdl bdl 0.091 0.126 bdl 0.0694 bdl 0.106 8.93 0.409 0.0275

10.8 17.1 70.8 3.45 212 42.0 61.4 40.0 280 17.7 0.036 bdl 0.912 6.94 1784 bdl bdl bdl 1.17 bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 6.30 bdl 0.363

0.433 0.885 681 17.5 376 41.7 2.62 76.9 bdl 6381 153 7.31 bdl 2.55 80.0 570 1286 163 841 198 64.5 1107 12.6 51.8 8.12 15.5 3.35 7.89 0.404 0.880 bdl 94.3 27.6 4.87

0.049 0.756 639 17.3 390 6.04 2.51 67.8 0.160 6169 139 7.49 0.244 4.36 68.2 263 561 69.2 363 101 39.0 671 8.77 38.8 6.41 13.0 3.10 13.0 0.672 bdl 0.093 87.1 2.36 4.61

0.098 bdl 798 29.2 465 17.4 2.50 72.8 bdl 5703 147 34.58 bdl 5.70 88.1 290 608 75.3 392 113 42.2 692 9.18 45.2 6.77 14.8 5.21 14.2 1.06 0.838 bdl 127 2.14 3.04

0.157 bdl 579 22.7 442 8.57 0.00 65.5 0.015 6831 110 17.84 bdl 2.44 131 195 375 45.3 234 78.4 30.8 546 7.61 31.7 5.04 7.75 2.40 3.88 0.915 0.435 bdl 126 0.19 2.53

0.097 0.609 474 22.5 235 46.2 2.45 104 bdl 9292 447 3.27 0.144 1.52 62.8 1203 2870 368 1937 465 153 2583 31.7 142 21.0 37.9 8.82 19.6 1.21 0.586 bdl 330 282 10.6

0.010 bdl 492 17.4 252 38.8 0.366 87.6 0.344 9723 323 2.58 bdl 1.76 81.5 737 1787 229 1232 305 102 1875 22.2 95.8 15.2 28.6 7.56 16.5 1.12 0.585 bdl 297 96.8 6.09

Ep-12

Ep-13

Ep-14

Ep-15

Ep-16

Aln-6

Aln-7

Aln-8

Aln-9

Aln-11

Aln-12

Aln-14

Aln-15

Aln-16

Aln-17

Aln-18

Aln-19

Aln-20

0.162 bdl 363 23.4 236 33.8 0.590

0.142 bdl 324 53.2 300 72.7 0.124

0.417 0.008 840 17.5 431 14.5 5.06

bdl 0.096 451 11.3 292 50.2 bdl

0.153 bdl 753 18.1 382 28.8 1.19

3.89 bdl 280 32.0 340 65.9 15.0

6.11 1.196 298 32.6 342 64.7 19.8

4.54 bdl 224 28.7 334 73.5 16.6

4.23 bdl 309 32.6 339 61.7 18.8

3.63 bdl 235 28.9 335 69.1 17.8

2.98 0.829 265 29.6 335 65.1 19.0

3.74 0.097 217 29.0 338 75.6 22.5

4.44 bdl 206 27.2 327 56.6 20.5

4.84 0.262 212 27.3 329 52.5 16.2

4.61 bdl 215 28.4 336 53.9 19.7

3.21 1.831 217 27.9 331 53.8 19.3

4.62 3.59 1.920 0.196 195 250 27.8 27.7 333 337 52.9 80.4 21.0 19.9 (continued on next page)

Li Be P Sc V Cr Ni

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx 9

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

Table 2 Trace element compositions of phengite, epidote and allanite from UHP quartzite at Qinglongshan in the Sulu orogen (ppm).

10

Ga Rb Sr Y Zr Nb Sn Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U

Ep-12

Ep-13

Ep-14

Ep-15

Ep-16

Aln-6

Aln-7

Aln-8

Aln-9

Aln-11

Aln-12

Aln-14

Aln-15

Aln-16

Aln-17

Aln-18

Aln-19

Aln-20

102.5 bdl 9565 347 4.67 0.0811 1.33 49.1 1252 2835 354 1784 404 132 2212 26.5 113 16.2 29.1 6.99 13.4 0.422 0.175 0.207 504 220 14.3

103.2 bdl 6954 513 5.86 bdl 6.30 37.6 1519 3242 396 2054 517 177 3174 39.6 168 24.4 44.1 9.58 25.1 1.15 1.07 bdl 400 86.3 14.1

76.9 0.292 4768 127 16.41 bdl 3.68 52.1 689 1678 210 1022 222 65.3 1093 11.5 46.1 6.12 11.3 1.52 6.23 0.206 0.197 bdl 115 78.7 2.20

79.5 bdl 8729 387 0.00 bdl 4.22 52.2 221 524 70.6 404 136 63.5 1201 19.2 102 15.9 34.4 8.29 20.7 1.10 bdl 0.013 271 12.5 6.46

73.9 bdl 6448 143 9.07 bdl 2.32 91.4 527 1169 146 728 172 58.8 971 10.9 48.7 6.81 15.4 3.19 10.6 0.38 0.525 0.090 106 31.6 4.57

561 bdl 4668 262 bdl bdl 7.67 22.3 19111 42994 4422 19689 3308 817 1542 86.8 169 11.4 10.6 0.279 0.495 0.14 bdl bdl 1413 749 580

579 bdl 4781 249 2.04 bdl 7.59 23.2 19978 44136 4551 20041 3310 802 1519 83.9 160 10.3 9.5 0.625 0.718 bdl 0.721 0.048 1368 824 598

589 bdl 4649 230 6.06 bdl 6.54 24.0 20862 45918 4678 20381 3308 777 1472 79.8 155 9.9 8.7 0.587 bdl 0.34 0.622 bdl 1289 798 565

579 bdl 4584 242 3.13 bdl 10.5 44.1 20472 45938 4701 20409 3366 793 1517 83.3 159 9.8 9.8 0.420 1.09 0.152 bdl bdl 1354 905 630

550 bdl 4660 248 3.85 bdl 5.55 20.1 18504 42583 4494 19786 3417 804 1560 87.1 170 10.8 9.6 0.423 1.68 0.199 bdl bdl 1296 831 681

540 bdl 4606 253 2.22 bdl 6.07 47.8 18346 42132 4462 19464 3335 799 1536 85.7 164 10.8 10.5 0.576 2.25 0.233 bdl bdl 1364 833 638

580 bdl 4761 229 2.64 bdl 5.81 24.8 20911 46275 4761 20551 3371 779 1483 80.7 152 9.8 7.6 0.370 bdl 0.105 bdl 0.074 1314 773 590

576 bdl 4821 207 bdl0 0.425 7.88 18.8 21288 46734 4737 20316 3226 748 1419 75.9 142 8.8 7.8 0.299 1.73 0.137 bdl 0.177 1305 685 521

576 0.415 4960 210 1.33 0.0243 5.92 23.7 21161 46090 4763 20327 3241 759 1433 76.8 142 9.2 7.8 0.421 1.45 0.213 bdl 0.061 1350 669 547

578 bdl 4710 242 2.42 bdl 7.81 22.0 20840 45802 4751 20686 3381 796 1552 85.7 159 10.0 9.3 0.541 1.95 0.366 bdl bdl 1349 705 553

571 bdl 4819 226 0.275 0.283 5.42 25.5 20793 45339 4731 20742 3323 783 1483 80.8 150 9.6 8.9 0.552 1.73 0.164 0.184 0.083 1324 625 569

569 bdl 4927 228 3.40 bdl 7.27 21.6 20569 44925 4694 20585 3342 777 1485 80.3 150 9.7 7.9 0.208 0.819 bdl bdl bdl 1362 573 539

557 0.258 5340 243 0.159 0.190 6.75 35.1 20615 44596 4671 20530 3375 819 1526 84.4 157 9.8 7.5 0.419 0.270 bdl bdl bdl 1602 802 561

Note: mineral abbreviations: Ph = phengite, Ep = epidote, Aln = Allanite; “bdl” denotes contents below the detection limit.

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

Table 2 (continued)

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

11

metamorphic origin (Rubatto, 2002; Zheng, 2009). Although there is a systematic difference in U–Pb ages between the zircon domains (Fig. 5b), there are no significant differences in their REE contents and patterns (Fig. 6a). The first group of zircon domains has Ti contents of 2.75–8.04 ppm, yielding Ti-in-zircon temperatures of 639–722 °C (Table 4), except one analysis that yields a Ti content of 21.0 ppm due to sampling of Ti-rich microscale mineral inclusions in zircon. The second group of zircon domains has Ti contents of 2.73–6.93 ppm, yielding Tiin-zircon temperatures of 638–710 °C (Table 4). It appears that there are no considerable differences in growth temperatures between the two groups of zircon. Fig. 4. Chondrite-normalized REE patterns for epidote and allanite from UHP metamorphic quartzite at Qinglongshan in the Sulu orogen. The chondrite values are after Sun and McDonough (1989).

contents of REE, with large LREE/HREE fractionation and no Eu anomalies (Table 2 and Fig. 4). 4.2. Zircon U–Pb ages and trace elements Zircon in the quartzite is generally euhedral to subhedral. Zircon grains are generally in sizes of 50–150 lm with aspect ratios of 1:1–5:1. Most zircon grains are oval, but a few are long and prismatic. In CL images, some grains exhibit the core–mantle–rim structure (Fig. 5a). The cores are mostly dark-grey with weak luminescence. The mantles are unzoned or weakly zoned, and are commonly embayed by the thin and bright rims. Generally, the core and mantle commonly exhibit sector zoning or fir-tree zoning. Homogenous but thin rims occur around the mantle domains, which are bright in CL images. While the outmost rim is too thin to be analysed, only nineteen U–Pb isotope analyses were obtained for cores and mantles of zircon from the quartzite (Table 3). This yields Th contents of 1.55–6.82 ppm and U contents of 35.1–172 ppm, with very low Th/U ratios of 0.05–0.11 for most analyses except two analyses (#4 and #8) that gave relatively high Th/U ratios of 0.13 and 0.17. In the U–Pb concordia diagram (Fig. 5b), the nineteen analyses yield two groups of nearly concordant U–Pb ages. The first group is composed of seven analyses giving 206Pb/238U ages of 237–248 Ma, with a weighted mean of 243 ± 4 Ma (n = 7, MSWD = 0.51). The second group is composed of twelve analyses yielding 206Pb/238U ages of 218–229 Ma, with a weighted mean of 223 ± 3 Ma (n = 12, MSWD = 0.35). The trace element composition of zircon domains was also analyzed (Table 4). The results exhibit relatively high contents of Hf (9783–11936 ppm), Y (46.7–77.3 ppm), Ti (0.60–21.0 ppm) and P (90.5–119 ppm), but relatively low contents of Nb (0–0.26 ppm) and Ta (<0.08 ppm). Their chondrite-normalized REE patterns are characterized by positive Ce anomalies, variable Eu anomalies and relatively steep MREE–HREE patterns (Fig. 6a). Their LREE contents are very low, with La and Pr close to the detection limits for some domains. Such REE patterns and low Th/U ratios (<0.2) indicate that these zircon domains are of

4.3. Rutile U–Pb ages and trace elements Rutile used in the U–Pb dating is a single megacrystal of about 15 mm in diameter. Seventy rutile U–Pb isotope analyses of the rim-core-rim profile were made by LA-MC-ICPMS (Table 5). As illustrated in Fig. 7, these U–Pb analyses yield a concordant age of 205.2 ± 1.6 Ma (MSWD = 0.67). In order to test the homogeneity of trace element distribution in the rutile, two core-rim profile analyses were performed by LA-ICPMS on another megacrystal rutile grain with a size of 10  22 mm from the same quartzite (Fig. 8), and the results are listed in Table 6. Before and after the analyses, back-scattered electron images were acquired and used to guide the analyses and ensure that the analytical locations were free of either ilmenite or zircon inclusions (Fig. 3b and c). Profile A is composed of 33 spots and profile B is composed of 21 spots. The results consistently show that the rutile grains have not only high HFSE contents such as Nb (468–750 ppm), Ta (20.1–31.3 ppm), Zr (110–138 ppm), Hf (3.9–6.0 ppm), and W (29.7–76.1 ppm), but also high contents of transition metal elements such as V (1194–1296 ppm), Cr (123–220 ppm) and Sc (2.2–3.8 ppm). In addition, small amounts of Sr (0.4–2.4 ppm) and U (1.9–9.2 ppm) were also detected in the rutile grains. REE and other trace elements have concentrations comparable to, or below, the detection limits. However, it is possible that the analyses showing the highest Fe contents result from sampling of microscale mineral inclusions in the forms of very tiny ilmenite or iron oxide lamellae or exsolved films (Zhang et al., 2009). These analyses were dealt with special carefulness though the systematic difference of trace element concentrations in question has not been found between these and the other analyses. For the megacrystal rutile grains, the core-rim profile exhibit remarkable compositional zoning for some trace elements (Table 6, and Figs. 8 and 9). The core yields relatively uniform and low contents of Nb (468–521 ppm), Ta (20.1–23.7 ppm), W (29.7–35.6 ppm), Sb (15.8–18.9 ppm), but relatively high U contents (5.9–9.2 ppm). In contrast, the rim gives relatively variable and generally high contents of Nb (605–750 ppm), Ta (23.3–31.3 ppm), W (40.0– 76.1 ppm), Sb (23.5–32.7 ppm) but relatively low U contents (1.9–5.8 ppm). As a consequence, the core and rim of profiles A and B exhibit very different trace element

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

12

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Fig. 5. CL images and Wetherill-type concordia U–Pb diagram for zircon from UHP metamorphic quartzite in the Sulu orogen. (a) Zircon CL images for quartzite; (b) U–Pb dating on the zircon mount by LA-ICPMS.

features in the diagrams of Nb, Ta, W, U and Sb (Fig. 8). Although Nb/Ta ratios for rutile rims and cores show considerable overlap with each other, the cores are generally characterized by low contents of HFSE with low Nb/Ta ratios of 20.6–24.8 whereas the rims exhibit relatively high HFSE contents with partly elevated and dispersive Nb/Ta ratios of 19.4–29.6 (Fig. 9). The measured Zr concentrations and corresponding Zr-in-rutile temperatures are listed in Table 6. The temperatures were calculated using the pressure-dependent Zrin-rutile thermometer of Tomkins et al. (2007), assuming a range of pressures from 1.5 to 4.5 GPa. The Zr contents of rutile domains exhibit a relatively small range from 110 to 138 ppm, with an average of 125 ppm. If calculated at

1.5–2.0 GPa assuming the unity activity of SiO2 and the saturation of zircon, the corresponding temperatures have a range of 600–640 °C. The Zr-in-rutile temperatures are significantly lower than the maximum metamorphic temperatures of 750–850 °C from petrological thermometries of the UHP metamorphic rocks at Qinglongshan (e.g., Zhang et al., 2005, 2009). 5. DISCUSSION 5.1. Zircon U–Pb ages and trace elements The zircon U–Pb dating for the quartzite yields two groups of concordant ages at 243 ± 4 and 223 ± 3 Ma,

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

13

Table 3 Mount LA-ICPMS analysis of U–Pb isotopes in zircon from UHP quartzite at Qinglongshan in the Sulu orogen. Spot no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

206

Pb* (ppm)

5.44 3.43 4.04 6.12 3.23 3.36 4.36 6.82 3.28 2.59 2.17 2.95 1.55 3.58 4.04 4.10 3.91 5.08 5.56

Th (ppm)

9.70 4.04 6.94 21.3 2.31 3.65 5.98 29.1 6.42 3.52 4.32 4.06 2.67 4.42 8.65 4.95 8.07 10.3 14.8

U (ppm)

150 76.9 109 166 91.2 91.2 100 172 85.8 76.0 61.9 84.0 35.1 62.2 101 97.1 101 135 139

Th U

0.07 0.06 0.06 0.13 0.03 0.04 0.06 0.17 0.08 0.05 0.07 0.05 0.08 0.07 0.09 0.05 0.08 0.08 0.11

Corrected isotope ratios 207

Apparent ages (Ma)

235

Error (1r)

206

206

Error (1r)

207

238

Error (1r)

0.0557 0.0476 0.0454 0.0640 0.0622 0.0379 0.0504 0.0469 0.0514 0.0426 0.0511 0.0677 0.05220 0.04906 0.04817 0.04457 0.05098 0.04990 0.05163

0.0045 0.0086 0.0081 0.0052 0.0091 0.0085 0.0094 0.0049 0.0084 0.0099 0.0102 0.0089 0.01146 0.00826 0.00335 0.00400 0.00480 0.00374 0.00357

0.2713 0.2542 0.2389 0.3036 0.2942 0.1728 0.2726 0.2397 0.2589 0.1974 0.2544 0.3274 0.27721 0.26106 0.23597 0.24098 0.24431 0.23641 0.24721

0.0231 0.0445 0.0440 0.0247 0.0441 0.0389 0.0433 0.0242 0.0416 0.0447 0.0495 0.0434 0.06860 0.09547 0.02906 0.03845 0.04543 0.03389 0.03485

0.0354 0.0388 0.0361 0.0348 0.0355 0.0357 0.0393 0.0384 0.0375 0.0350 0.0355 0.0352 0.03852 0.03859 0.03553 0.03921 0.03476 0.03436 0.03473

0.0006 0.0008 0.0008 0.0005 0.0008 0.0007 0.0009 0.0006 0.0007 0.0008 0.0009 0.0007 0.00165 0.00118 0.00095 0.00121 0.00099 0.00086 0.00090

*

Pb Pb*

*

Pb U

*

Pb U

207

207

206

206

235

238

Pb Error U (1r)

439 78 32 742 682 493 211 44 257 189 244 859 294 151 108 79 240 190 269

181 432 434 171 313 599 431 248 375 579 460 273 501 394 164 220 217 174 159

Pb Error U (1r)

244 230 218 269 262 162 245 218 234 183 230 288 248 236 215 219 222 215 224

23 44 44 25 44 39 43 24 41 44 49 43 67 93 29 38 45 34 35

Pb Error U (1r)

224 245 229 221 225 226 248 243 237 222 225 223 244 244 225 248 220 218 220

4 5 5 3 5 5 6 4 5 5 6 5 11 8 6 8 6 6 6

Notes: Pb* indicates the radiogenic portions.

respectively (Fig. 5b). While the second group of younger ages is overlapping with those obtained for UHP quartzites in the same locality (Chen et al., 2013a), the first group of older ages is reported for the first time in this region. Notably, the two groups of zircon domains in the quartzite give identical Ti-in-zircon temperatures of 638–722 °C (Table 4), suggesting that the two episodes of zircon growth occur at the similar temperatures. The two groups of zircon domains exhibit generally low Th/U ratios of 0.05–0.11, suggesting their growth mainly from metamorphic fluid rather than magmatic melt (Xia et al., 2009; Chen et al., 2010, 2012; Li et al., 2013). They show steep MREE–HREE patterns, indicating their growth with negligible garnet effect (Rubatto, 2002; Rubatto and Hermann, 2007; Zheng, 2009). Because metamorphic quartzite is generally produced by precipitating quartz crystals from silica-saturated aqueous solutions, metamorphic dehydration is evident for local sinking of the aqueous solutions during the Triassic continental collision. The same two groups of zircon U–Pb ages at 240–245 and 220–225 Ma have been reported for UHP metamorphic rocks from the Dabie-Sulu orogenic belt (Zheng et al., 2005; Wan et al., 2005; Liu et al., 2006; Wu et al., 2006; Gao et al., 2011). Because the peak UHP metamorphic event in the coesite stability field has been well constrained to took place at 240–225 Ma for the Dabie-Sulu orogenic belt (Zheng et al., 2009; Liu and Liou, 2011), the two groups of zircon U–Pb ages have been interpreted as dating the two episodes of zircon growth, respectively, during prograde subduction from HP to UHP eclogite facies and retrograde exhumation from UHP to HP eclogite facies. Unlike HP to UHP eclogites that underwent metamorphism dehydration during subduction, the formation of

quartzite during subduction-zone metamorphism requires local sinking of silica-rich solutions into fractures. In other words, the dehydration during the eclogite-facies metamorphism serves as the source of aqueous solutions (leaving the eclogites as restites), whereas the formation of quartzite in the fractures witnesses the sink of aqueous solutions in eclogite-facies metamorphic rocks. As such, the growth of metamorphic zircon in the quartzite provides temporal records of the fluid action during the continental collision. Therefore, the two groups of zircon U–Pb ages at 243 ± 4 and 223 ± 3 Ma for the Sulu quartzite are interpreted as recording the two episodes of fluid action, respectively, during prograde subduction prior to the UHP phase and retrograde exhumation subsequent to the UHP phase. Nearly consistent ages of 219.6 ± 1.4–223.0 ± 0.9 Ma were obtained by garnet Lu–Hf dating for UHP eclogites in the Dabie-Sulu orogenic belt (Schmidt et al., 2008, 2011). It appears that the younger group of zircon U–Pb ages at 223 ± 3 Ma for the quartzite is contemporaneous with the reequilibration of garnet Lu–Hf radiometric system in the eclogites. This is consistent with the action of metamorphic fluid on retrograde HP eclogite-facies recrystallization at that time (Zhao et al., 2006; Zheng, 2009). Thus, the reequilibration of mineral Lu–Hf radiometric systems was achieved at the second episode of fluid action during the exhumation (Zheng, 2012). On the other hand, the U–Pb radiometric systems of metamorphic zircon are very resistant subsequent to its crystallization from HP to UHP geofluids (Zheng, 2009). In this regard, the mineral Lu–Hf systems are more susceptible to resetting than the zircon U–Pb systems. Therefore, the zircon U–Pb ages provide a geochronological reference framework for the interpretation of rutile U–Pb age and trace element composition.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

14

Spot no.

Li

P

Ti

Sr

Y

Hf

Nb

Ta

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

T (°C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

1.21 0.61 0.91 0.47 0.81 0.39 0.56 0.81 1.52 0.86 0.42 0.78 0.13 2.72 0.51 0.18 0.44 0.21 0.44

97.8 104.5 90.5 95.6 112.6 117.2 106.8 96.3 91.6 104.7 118.5 99.8 93.9 116 103 102 101 93.5 119

3.51 2.75 4.96 6.93 4.11 5.95 4.81 3.48 8.04 4.01 3.31 2.73 4.87 21.0 6.14 5.39 3.83 3.22 5.06

bdl 0.087 0.094 bdl 0.102 0.056 bdl bdl 0.161 0.075 0.094 bdl 0.034 0.332 0.099 0.092 0.079 0.10 0.11

76.7 55.7 57.0 74.2 46.8 48.0 52.3 74.1 69.2 73.2 58.2 77.3 49.7 52.3 46.7 67.6 49.2 74.8 69.6

11554 11936 10808 11756 11357 11282 10368 10695 10951 11572 11572 11247 10198 9820 10232 9783 9831 10011 10227

bdl bdl 0.088 bdl bdl 0.036 0.10 0.0036 bdl 0.11 0.19 bdl 0.092 0.20 0.12 0.082 0.16 0.095 0.26

bdl 0.026 bdl bdl bdl 0.0015 bdl bdl bdl 0.016 0.075 0.046 bdl 0.051 0.015 0.020 0.029 0.005 0.074

bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 0.033 0.01 0.041 0.061 0.025 0.035 0.047

0.62 0.56 0.78 1.05 0.45 0.70 0.69 1.71 0.96 1.57 1.36 1.87 1.02 0.59 0.75 0.68 0.73 1.04 1.11

bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 0.056 0.04 0.002 0.005 0.004 0.010 0.011

bdl bdl bdl bdl bdl bdl 0.54 bdl bdl 0.097 0.32 0.50 0.290 0.19 0.14 0.064 0.056 0.049 0.093

bdl bdl 0.060 bdl 0.16 bdl bdl bdl bdl 0.19 bdl bdl 0.264 0.14 0.14 0.073 0.286 0.113 0.145

0.053 bdl bdl 0.29 bdl bdl 0.048 0.19 bdl bdl bdl 0.18 0.074 0.21 0.051 0.042 0.071 0.16 0.13

0.73 0.77 bdl 1.20 0.49 0.61 0.58 1.65 bdl 0.44 0.96 1.10 0.77 1.90 0.78 0.76 0.73 1.53 0.74

0.33 0.28 0.41 0.40 0.17 0.22 0.26 0.82 0.27 0.26 0.30 0.47 0.33 0.36 0.32 0.38 0.30 0.59 0.39

5.45 3.91 4.04 5.97 3.50 3.59 4.16 7.27 5.23 5.93 3.80 5.65 4.32 4.50 4.49 5.31 4.27 7.03 4.54

2.36 1.65 1.78 2.30 1.27 1.53 1.65 2.30 2.11 2.23 1.81 2.25 1.58 1.69 1.49 2.03 1.54 2.36 2.05

10.3 6.96 7.27 8.96 5.77 6.06 6.45 8.34 9.37 9.98 7.76 10.2 7.33 6.84 5.59 8.48 5.87 10.0 9.9

2.20 1.26 1.58 1.61 1.08 1.09 1.29 1.37 1.98 2.21 1.89 2.49 1.24 1.63 1.17 1.57 1.08 1.92 2.34

19.8 11.2 11.7 13.7 9.53 9.54 11.1 12.5 17.6 20.2 15.0 21.1 10.4 15.6 9.5 15.1 9.2 14.5 23.2

3.69 2.06 2.38 2.55 1.50 1.66 2.11 2.19 3.85 3.61 3.05 3.87 1.48 2.41 1.52 2.09 1.41 2.17 3.98

657 639 683 710 668 697 681 656 722 667 652 638 681 811 700 689 663 650 684

Note: “bdl” denotes contents below the detection limit; Temperature was calculated after Ferry and Watson (2007), assuming aTiO2 = 1 and aSiO2 = 1.

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

Table 4 LA-ICPMS analysis of trace elements in zircon from UHP quartzite at Qinglongshan in the Sulu orogen.

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Fig. 6. Trace element distribution of zircon from UHP metamorphic quartzite in the Sulu orogen. (a) Chondrite-normalized REE pattern, and (b) primitive mantle-normalized trace element pattern. The chondrite and primitive mantle values are from Sun and McDonough (1989).

5.2. Rutile U–Pb ages The studied rutile has significant U contents of 1.9– 9.2 ppm with homogeneous U–Pb isotope compositions across the megacrystal grain (Table 6 and Fig. 7). The rutile U–Pb dating yields a concordant age of 205 ± 2 Ma (MSWD = 0.67), which is significantly lower than the younger group of zircon U–Pb ages at 223 ± 3 Ma. Previous studies have demonstrated that rutile in high-grade metamorphic rocks tends to exhibit younger U–Pb ages than coexisting zircon and titanite U–Pb ages and even hornblende Ar/Ar ages (Mezger et al., 1991; Corfu and Easton, 1995; Cox et al., 1998, 2002; Christofell et al., 1999; Connelly et al., 2000; Norcross et al., 2000; Bibikova et al., 2001; Hirdes and Davis, 2002; Schmitz and Bowring, 2003; Zack et al., 2011). This was ascribed to the high rate of radiogenic Pb diffusion in rutile and thus to the low closure temperature of U–Pb radiometric system in the mineral. The closure temperature of Pb diffusion in rutile is quantitatively dependent on grain size and cooling rate (Dodson, 1973; Mezger et al., 1991; Cherniak, 2000). A compilation of previous estimates for the closure temperatures of Pb diffusion (TC) in rutile is illustrated in Fig. 10. Based on the U–Pb dating of rutile and the cooling history of natural

15

granulites, Mezger et al. (1989) estimated a closure temperature between 370 and 500 °C for the diffusion of radiogenic Pb in rutile with grain radii of 90–210 lm and cooling rates of 1–2 °C/Ma, and somewhat lower closure temperatures for smaller rutile grains of 70–90 lm. Based on the same data from Mezger et al. (1989), however, Vry and Baker (2006) reestimated TC values of 500–540 °C for rutile in the granulites. Li et al. (2003) obtained a TC value of 460 °C for rutile U–Pb system in eclogite under rapid cooling conditions (20 °C/Ma). Kooijman et al. (2010) gave variable TC values from 640 °C in core and 490 °C in rim rutile during slow cooling (0.4–2.2 °C/Ma). Based on her experimental diffusion data, Cherniak (2000) gave a TC value of 567 °C for a rutile grain of 70 lm and 617 °C for a rutile grain of 200 lm under anhydrous conditions, and higher than 600 °C under hydrous conditions. The above results indicate higher closure temperatures of Pb diffusion in rutile than previous estimates. The Zr-in-rutile temperatures of 605–688 °C are calculated for rutile at 1.5–4.5 GPa (Table 6). It is noted the effect of pressure on the calculated temperatures is insignificant even at UHP conditions. For instance, the temperatures calculated at 2.5 and 3.0 GPa only differs up to about 5 °C at 630–650 °C. If estimated at UHP conditions (3.0 GPa) assuming the unity activity of SiO2 and the saturation of zircon, the corresponding temperatures have a range of 650–667 °C. Such temperatures are significantly lower than the peak metamorphic temperature of 750–850 °C (e.g., Zhang et al., 2005; Zheng, 2008), indicating that the rutile would not grown at the peak UHP conditions. Instead, the rutile would grow at lower pressures of 1.5–2.0 GPa, corresponding to the Zr-in-rutile temperatures of 600–640 °C (Fig. 11). Our studied megacrystal rutile in the quartzite has a rather large size (10 mm), which would lead to higher TC in the core if this is taken as the effective diffusion radius. In addition, there are many cracks in the rutile megacrystals (Fig. 3), subdividing individual grains into many isolated small parts. These small parts can be considered as the effective diffusion units in the size of 100–200 lm. In this case, the closure temperature of Pb diffusion in our rutile can be estimated from the experimental diffusion coefficients of Cherniak (2000), which is in a range of 600–650 °C at a cooling rate of <10 °C/Ma (Fig. 10). Such temperatures are indistinguishable from the Zr-in-rutile temperatures of 600–640 °C at 1.5–2.0 GPa (Fig. 11), suggesting that the rutile U–Pb age has dated its growth, a kind of rapid cooling. Although the rutile U–Pb age of 205 ± 2 Ma is significantly younger than the younger group of U–Pb ages at 223 ± 3 Ma, a scenario of slow cooling from the rutile growth at 223 ± 3 Ma to the Pb diffusion closure at 205 ± 2 Ma is not applicable to the large time interval of 15–20 Myr with a small thermal gradient of 5–10 °C. Therefore, the rutile U–Pb age dates the closure time of Pb diffusion subsequent to its growth during the exhumation. It has been well established that the UHP metamorphic rocks in the Sulu orogen achieved the maximum temperatures of 750–850 °C (e.g., Zhang et al., 2005, 2009; Xu et al., 2006; Liu and Liou, 2011). Such temperatures occur in the stage of exhumation and are responsible for anatexis

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

16

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Table 5 LA-MC-ICPMS U–Pb isotope data for rutile from UHP quartzite at Qinglongshan in the Sulu orogen. Spot no.

Corrected isotope ratios 207

238

206

Error (1r)

207

235

Error (1r; %)

207

206

Error (1r; %)

206

206

Error (1r; %)

207

0.0500 0.0489 0.0488 0.0494 0.0506 0.0496 0.0494 0.0492 0.0508 0.0484 0.0473 0.0492 0.0494 0.0485 0.0484 0.0482 0.0497 0.0484 0.0489 0.0502 0.0500 0.0498 0.0493 0.0501 0.0510 0.0544 0.0504 0.0514 0.0509 0.0481 0.0500 0.0506 0.0528 0.0479 0.0479 0.0509 0.0511 0.0505 0.0501 0.0532 0.0508 0.0533 0.0516 0.0519 0.0530 0.0516 0.0539 0.0542 0.0509 0.0536 0.0565 0.0529 0.0512 0.0502 0.0493 0.0477 0.0491 0.0505

2.8 2.9 2.9 2.9 3.0 2.9 3.2 2.9 2.8 2.9 3.1 2.9 2.9 3.8 2.9 2.9 3.0 3.1 2.9 3.0 2.9 3.3 2.9 3.0 2.9 2.8 2.9 3.0 3.9 2.9 2.9 5.7 3.4 4.4 3.0 3.1 3.1 2.9 3.0 3.3 3.1 3.1 3.2 2.8 4.1 2.9 2.8 3.7 2.9 3.1 3.9 2.9 3.3 3.7 3.5 3.2 3.3 3.1

0.2233 0.2138 0.2221 0.2203 0.2267 0.2223 0.2184 0.2188 0.2292 0.2158 0.2104 0.2144 0.2164 0.2146 0.2154 0.2128 0.2180 0.2155 0.2134 0.2237 0.2252 0.2219 0.2174 0.2239 0.2283 0.2525 0.2308 0.2346 0.2287 0.2122 0.2318 0.2233 0.2407 0.2111 0.2124 0.2271 0.2260 0.2230 0.2242 0.2455 0.2256 0.2443 0.2347 0.2357 0.2439 0.2288 0.2426 0.2404 0.2313 0.2393 0.2533 0.2438 0.2323 0.2301 0.2143 0.2167 0.2183 0.2246

3.7 3.7 3.8 3.8 3.9 3.7 4.0 3.8 3.7 3.8 3.9 3.8 3.8 4.5 3.7 3.8 3.8 3.9 3.7 3.8 3.8 4.1 3.8 3.8 3.7 3.7 3.7 3.9 4.6 3.7 3.8 6.2 4.1 5.0 3.8 3.9 3.9 3.8 3.8 4.1 3.9 3.9 4.0 3.7 4.7 3.8 3.7 4.4 3.8 3.9 4.6 3.8 4.1 4.5 4.2 4.1 4.1 3.9

0.0324 0.0317 0.0330 0.0323 0.0325 0.0325 0.0321 0.0322 0.0327 0.0324 0.0323 0.0316 0.0318 0.0321 0.0323 0.0320 0.0318 0.0323 0.0317 0.0323 0.0326 0.0323 0.0320 0.0324 0.0325 0.0336 0.0332 0.0331 0.0326 0.0320 0.0336 0.0320 0.0330 0.0320 0.0322 0.0324 0.0321 0.0320 0.0325 0.0335 0.0322 0.0332 0.0330 0.0330 0.0334 0.0322 0.0326 0.0322 0.0329 0.0324 0.0325 0.0334 0.0329 0.0333 0.0315 0.0330 0.0322 0.0323

2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.3 2.4 2.4 2.4 2.4 2.5 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.5 2.4 2.5 2.5 2.4

195 141 140 168 225 175 166 160 233 116 64 159 167 124 119 107 180 120 141 205 196 184 160 201 239 389 213 259 237 103 195 223 321 94 94 235 244 217 198 337 234 343 267 279 329 267 367 378 238 354 472 324 250 202 162 83 153 217

65 66 66 66 68 66 74 67 64 67 73 67 67 88 66 68 68 72 66 68 66 74 67 68 65 62 65 68 87 67 67 127 75 101 69 70 71 66 68 73 71 69 71 63 90 66 62 82 66 69 85 65 74 84 79 74 76 70

205 197 204 202 208 204 201 201 210 198 194 197 199 197 198 196 200 198 196 205 206 204 200 205 209 229 211 214 209 195 212 205 219 195 196 208 207 204 205 223 207 222 214 215 222 209 221 219 211 218 229 222 212 210 197 199 201 206

Pb Pb

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

Apparent age (Ma)

208

0.01180 0.00129 0.00159 0.00254 0.00218 0.00380 0.00510 0.00160 0.00503 0.00082 0.00389 0.00097 0.00162 0.01180 0.00180 0.00241 0.00045 0.00261 0.00006 0.00333 0.00360 0.00758 0.00207 0.00328 0.01035 0.02456 0.00421 0.00524 0.00424 0.00511 0.00238 0.00913 0.00770 0.01103 0.00401 0.00162 0.00487 0.00168 0.00257 0.00731 0.00354 0.00690 0.02378 0.01862 0.00182 0.01147 0.00262 0.00804 0.01145 0.00268 0.09486 0.00831 0.01522 0.00417 0.02238 0.02374 0.00442 0.00159

Pb Pb

Pb U

Pb U

Pb Pb

Pb U

235

Error (1r)

206

Pb U

238

Error (1r)

7 206 5 7 201 5 7 209 5 7 205 5 7 206 5 7 206 5 7 204 5 7 204 5 7 207 5 7 205 5 7 205 5 7 200 5 7 202 5 8 204 5 7 205 5 7 203 5 7 202 5 7 205 5 7 201 5 7 205 5 7 207 5 8 205 5 7 203 5 7 206 5 7 206 5 8 213 5 7 211 5 7 210 5 9 207 5 7 203 5 7 213 5 12 203 5 8 210 5 9 203 5 7 204 5 7 205 5 7 204 5 7 203 5 7 206 5 8 212 5 7 204 5 8 211 5 8 209 5 7 209 5 9 212 5 7 204 5 7 207 5 9 204 5 7 209 5 8 205 5 9 206 5 8 212 5 8 209 5 9 211 5 8 200 5 7 209 5 8 205 5 7 205 5 continued on next page

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

17

Table 5 (continued) Spot no.

Corrected isotope ratios 207

206

235

Error (1r)

206

238

Error (1r)

207

235

Error (1r; %)

207

206

Error (1r; %)

206

206

Error (1r; %)

207

238

Error (1r)

0.0521 0.0491 0.0506 0.0512 0.0532 0.0490 0.0519 0.0485 0.0558 0.0497 0.0507 0.0490

3.2 3.2 3.5 3.7 3.1 3.1 3.8 3.0 3.9 3.2 4.7 2.8

0.2316 0.2150 0.2206 0.2251 0.2356 0.2143 0.2267 0.2167 0.2478 0.2195 0.2222 0.2257

4.0 4.0 4.2 4.5 3.9 3.9 4.5 3.9 4.6 4.0 5.3 3.6

0.0322 0.0318 0.0316 0.0319 0.0321 0.0317 0.0317 0.0324 0.0322 0.0320 0.0318 0.0334

2.4 2.4 2.4 2.5 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.3

289 153 224 250 339 147 280 124 444 182 228 149

71 72 78 84 68 71 84 70 85 73 105 64

212 198 202 206 215 197 208 199 225 202 204 207

8 7 8 8 8 7 8 7 9 7 10 7

205 202 201 202 204 201 201 206 204 203 202 212

5 5 5 5 5 5 5 5 5 5 5 5

Pb Pb

59 60 61 62 63 64 65 66 67 68 69 70

Apparent age (Ma)

208

0.00064 0.00219 0.00809 0.01734 0.00136 0.00615 0.00807 0.01848 0.00155 0.00945 0.00266 0.02809

Pb Pb

Pb U

Fig. 7. U–Pb concordia diagram for rutile from UHP metamorphic quartzite at Qinglongshan in the Sulu orogen.

of the UHP rocks (Chen et al., 2013a,b). They are significantly higher than the closure temperatures of 600–650 °C for Pb diffusion in rutile (Fig. 10), the Zr-in-rutile temperatures of 600–640 °C and the Ti-in-zircon temperatures of 638–710 °C. In this regard, the younger group of zircon domains may have grown from hydrous melts during the exhumation (Chen et al., 2013a,b). Nevertheless, the rutile would have grown from aqueous solutions during the further exhumation. In view of the known P–T–t path for UHP slices in the Dabie-Sulu orogenic belt (Zheng, 2008; Liu and Liou, 2011), it is possible that the rutile U–Pb age of 205 ± 2 Ma has dated the termination of fluid action during the exhumation. 5.3. Rutile trace elements There are two types of trace element zonation in the megacrystal rutiles: (1) the remarkable increase of Nb, Ta, W and Sb contents and slightly high Nb/Ta ratios from core to rim (Figs. 8 and 9); (2) the remarkable decrease of U contents from core to rim (Fig. 8). Trace element zoning could be formed either during growth or by diffusion. The growth zoning is probably driven by changes in reservoir composi-

Pb U

Pb Pb

Pb U

Pb U

tion or in pressure/temperature, resulting in the change of element partitioning during growth of the mineral (Kohn, 2003; Ding et al., 2009). The diffusion zoning is caused by the difference in chemical potential, where a pre-existing grain is modified in composition by exchange of material with the rock matrix. According to the diffusion rate of Zr in rutile (Cherniak et al., 2007), the diffusion loss of Zr from rutile is very unlikely during eclogite-facies metamorphism. For instance, using the experimental diffusion coefficients of Cherniak et al. (2007) for Zr in rutile, complete resetting of Zr distribution in rutile at 750 °C requires 15.5 Myr for a small rutile grain in a size of 100 lm and 62.2 Myr for a large grain in a size of 200 lm. Thus, the significant enrichment of such trace elements as Nb, Ta, Sb and W in the rim (Fig. 8 and Table 6) cannot be ascribed to the diffusion effect. Instead, it is more likely a result of growth zoning. The formation of rutile in metamorphic rocks during continental collision is generally controlled by a number of mineralogical reactions (Zheng et al., 2011a), including the ilmenite- and titanite-consuming reactions with anhydrous minerals such as anorthite, quartz, kyanite or pyrope, or the reactions between titanite and hydrous minerals such as zoisite and muscovite (Meinhold, 2010; Zheng et al., 2011a). Dehydration metamorphism is a common mechanism for the rutile formation in subduction-zone HP to UHP eclogites. In the present case, however, the rutile occurs in the UHP quartzite that is petrogenetically associated with fluid sinking. Thus, it is possible for rutile to grow from different compositions of metamorphic fluid during the subduction and exhumation of continental crust. Because the breakdown of hydrous minerals is a predominated source of aqueous solutions in UHP metamorphic rocks, the property of hydrous minerals is a key to the composition of metamorphic fluids. The enrichment of water-insoluble incompatible trace elements such as Nb, Ta, Sb and W with slightly high Nb/Ta ratios in the rims of rutile may be caused by one of the following mechanisms: (1) retrogression of UHP rutile to ilmenite during metamorphism (Ague et al., 2013); (2) breakdown of UHP hydrous minerals such as phengite and biotite (Stepanov and Hermann, 2013). The first mechanism is substantially dictated by the nature of

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

18

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Fig. 8. Rim–core–rim profile analyses of rutile grains from UHP metamorphic quartzite in the Sulu orogen. (a) A1–A33 profile of rutile; (b) B1–B21 profile of rutile.

mineralogical reactions, whereas the second mechanism is equivalent to crystallization from a kind of geofluids that has high contents of water-insoluble trace elements (Zheng et al., 2011b). During the retrogression of UHP rutile to ilmenite, Ti is sequestered by ilmenite whereas

Nb and Ta are retained in rutile. This process does not change the Nb/Ta ratios of rutile. In addition, ilmenite does not occur as retrograde corona in the rutile rim (Fig. 3). Therefore, the first mechanism is unlikely to cause the Nb/Ta variation in the megacrystal rutile.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

19

Table 6 LA-ICPMS analysis of major and trace elements in rutile from UHP quartzite at Qinglongshan in Sulu orogen. Spot Sc V Cr Sr Zr Nb Sb Hf Ta W U Nb/ Zr/ T1.5 T2.0 T2.5 T3.0 T3.5 T4.5 no. (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) Ta Hf ‘(°C) (°C) (°C) (°C) (°C) (°C) A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15 A16 A17 A18 A19 A20 A21 A22 A23 A24 A25 A26 A27 A28 A29 A30 A31 A32 A33

2.66 3.00 3.38 2.56 3.12 3.30 2.85 3.34 3.22 2.56 2.74 2.40 2.78 3.26 3.06 2.78 2.37 2.89 3.03 3.23 2.80 2.41 3.04 3.85 3.27 2.77 2.30 3.17 2.68 2.27 2.92 2.98 2.84

1223 1197 1201 1218 1239 1233 1219 1229 1244 1224 1245 1239 1267 1237 1239 1261 1278 1244 1239 1215 1255 1259 1232 1250 1252 1219 1222 1230 1230 1253 1228 1242 1194

156 158 145 151 178 172 201 220 186 184 185 170 144 183 184 179 188 182 173 166 180 164 176 186 166 195 165 187 169 141 139 168 212

0.62 0.53 0.43 0.65 0.73 0.77 0.54 0.45 0.51 0.60 0.41 0.60 0.69 0.92 0.51 0.74 0.77 0.54 1.77 1.48 0.85 0.60 2.37 0.55 0.62 0.64 0.43 0.51 0.60 0.53 0.59 0.70 0.63

119 119 118 119 124 122 123 132 131 128 127 128 126 123 123 124 128 125 120 123 125 126 124 131 124 121 129 120 125 122 123 117 110

730 692 656 645 479 492 492 494 493 491 486 486 484 486 500 503 511 508 497 521 505 505 496 504 506 488 494 472 468 632 616 606 628

27.9 29.9 28.5 28.5 16.9 15.9 17.1 17.3 17.2 15.9 16.5 16.2 16.8 17.7 15.9 18.1 16.3 16.4 17.5 18.9 18.1 18.3 16.8 17.3 17.2 18.0 17.4 16.8 17.7 31.9 26.7 32.7 32.7

4.88 4.46 4.59 4.61 4.91 5.52 4.86 5.51 5.42 5.44 5.43 5.00 5.52 4.56 5.22 5.15 5.15 5.03 5.64 5.74 5.29 5.09 5.40 5.24 5.17 5.68 5.31 4.89 5.39 4.27 4.55 4.72 4.84

24.6 24.7 24.8 23.9 21.4 21.9 22.5 22.4 21.8 21.2 21.4 20.8 20.5 20.7 21.6 21.7 21.9 21.1 20.1 22.6 22.3 21.6 22.6 23.0 22.6 23.7 22.2 21.2 22.5 24.1 25.3 31.3 31.0

50.2 52.0 53.8 47.9 30.1 30.8 31.5 30.9 29.7 30.7 30.0 30.4 30.4 29.8 31.2 31.6 30.4 29.8 30.2 35.6 35.3 33.6 35.2 34.3 34.5 34.4 32.8 31.4 31.0 47.0 49.2 68.1 76.1

1.91 4.87 5.55 5.02 6.88 7.60 6.78 7.24 7.59 6.92 7.75 6.65 7.51 6.74 7.33 7.98 7.41 7.56 7.42 7.48 7.35 7.81 7.40 9.18 7.06 7.10 6.82 6.80 5.75 5.14 4.42 3.35 1.97

29.6 28.0 26.4 27.0 22.4 22.5 21.8 22.1 22.6 23.2 22.7 23.3 23.7 23.5 23.2 23.2 23.3 24.1 24.8 23.1 22.6 23.3 21.9 21.9 22.4 20.6 22.2 22.2 20.8 26.2 24.3 19.4 20.3

24.3 26.7 25.8 25.8 25.3 22.1 25.2 24.0 24.2 23.5 23.5 25.6 22.8 26.9 23.5 24.0 24.9 24.8 21.3 21.4 23.6 24.7 22.9 25.0 23.9 21.2 24.3 24.6 23.2 28.5 27.0 24.8 22.6

606 606 606 606 609 608 608 613 613 611 611 611 610 608 608 609 611 609 607 608 609 610 609 613 609 607 612 607 609 608 608 605 600

628 629 628 629 632 630 631 636 635 634 633 634 632 631 631 631 634 632 629 631 632 632 631 635 631 629 634 629 632 630 631 627 623

651 651 650 651 654 653 653 658 658 656 656 656 655 653 653 654 656 654 652 653 654 655 654 658 654 652 657 652 654 652 653 650 645

656 656 656 656 659 658 659 664 663 662 661 662 660 659 659 659 662 660 657 659 660 661 659 664 659 657 662 657 660 658 659 655 650

666 666 666 666 670 668 669 674 674 672 672 672 671 669 669 669 672 670 667 669 670 671 669 674 669 667 673 667 670 668 669 665 660

676 677 676 677 680 678 679 685 684 682 682 682 681 679 679 679 682 680 677 679 680 681 680 684 679 678 683 677 680 678 679 675 670

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 B13 B14 B15 B16 B17 B18 B19 B20 B21

2.80 2.55 3.60 2.74 3.24 2.94 3.17 2.55 3.30 2.51 2.24 3.22 2.99 3.01 3.20 3.10 3.35 3.45 2.41 2.45 2.19

1280 1229 1296 1246 1242 1277 1296 1293 1283 1246 1272 1277 1261 1243 1259 1250 1246 1212 1209 1216 1205

147 179 175 204 179 185 178 181 174 171 188 162 168 176 180 176 165 167 160 123 173

0.72 0.57 0.51 0.52 0.69 0.62 0.51 0.66 0.60 0.60 0.39 0.69 0.67 0.63 0.55 0.52 0.45 0.43 0.45 0.55 0.59

117 121 125 133 125 128 131 117 123 133 126 124 128 129 133 120 135 125 128 119 138

605 626 750 493 485 484 484 499 497 497 493 509 521 519 502 474 487 472 477 667 648

23.5 25.9 28.1 16.9 16.1 16.6 17.6 17.4 16.6 17.5 17.3 15.8 18.2 16.6 18.1 16.5 16.3 17.5 15.9 27.5 28.8

4.40 3.92 5.73 5.12 5.14 4.76 4.97 5.06 5.05 5.06 5.06 5.32 5.12 6.02 5.50 5.09 5.53 5.39 5.19 4.70 5.87

23.3 25.2 29.1 22.5 22.6 22.7 22.9 22.3 23.3 22.9 22.7 22.6 22.6 22.4 22.8 22.8 23.5 22.7 21.3 26.2 29.6

40.0 47.5 53.3 29.7 33.2 32.3 32.8 32.1 33.9 34.4 32.5 33.6 33.7 33.9 33.8 32.4 34.0 32.8 30.0 51.4 70.5

4.11 5.32 5.81 6.81 6.73 6.83 7.16 6.82 6.63 7.21 7.48 7.13 7.27 7.56 7.22 6.82 6.70 6.08 5.55 3.50 2.63

26.0 24.9 25.8 21.9 21.4 21.3 21.1 22.3 21.3 21.7 21.7 22.5 23.1 23.2 22.1 20.8 20.7 20.8 22.4 25.4 21.9

26.7 30.9 21.9 25.9 24.3 26.9 26.3 23.1 24.4 26.3 24.9 23.3 24.9 21.4 24.2 23.6 24.3 23.1 24.7 25.4 23.5

605 607 610 614 610 611 613 605 609 614 610 609 611 612 614 607 615 609 611 606 616

627 630 632 636 632 634 635 627 631 636 633 631 633 634 637 629 637 632 634 629 639

650 652 655 659 655 656 658 650 653 659 655 654 656 657 659 652 660 654 656 651 662

655 658 660 665 660 662 663 655 659 665 661 659 662 662 665 657 666 660 662 656 667

665 668 670 675 670 672 674 665 669 675 671 669 672 672 675 667 676 670 672 667 678

675 678 681 685 680 682 684 675 679 685 681 680 682 683 685 677 686 680 682 677 688

Notes: T1.5, T2.0, T2.5, T3.0, T3.5 and T4.5 denote the Zr-in-rutile temperatures at 1.5, 2.0, 2.5, 3.0, 3.5 and 4.5 GPa, respectively, calculated by the calibration of Tomkins et al. (2007).

As phengite is able to contain 1–2 wt.% TiO2 and about 10 ppm Nb (Hermann and Spandler, 2008), its breakdown can produce rutile rims with 100 wt.% TiO2 and 700 ppm

Nb in the extreme case. Natural observations did show that UHP metamorphic phengite breaks down to form kyanite + rutile + K-feldspar + melt during decompression

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

20

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Fig. 9. Plots of trace element relationships for rutile grains from UHP metamorphic quartzite in the Sulu orogen. (a) Ta versus Nb; (b) W versus Sb; (c) Nb/Ta versus Nb; (d) Nb/Ta versus U. Also shown are Nb/Ta ratios for the primitive mantle (McDonough and Sun, 1995) and the continental crust (Rudnick and Gao, 2003).

Fig. 10. A compilation of closure temperature estimates for Pb diffusion in rutile. Curves denote the different cooling rates (diffusion coefficients after Cherniak, 2000). Data sources for field-based closure temeratures: 1 – Mezger et al. (1989); 2 – Mezger et al. (1989) values as recalculated by Vry and Baker (2006); 3 – Li et al. (2003); 4 – Li et al. (2011); 5 (rim) -, 6 (core) – Kooijman et al. (2010); 7 – Cherniak (2000); 8 – Vry and Baker (2006); 9 – this study.

exhumation (Lang and Gilotti, 2007). The experimental study of Stepanov and Hermann (2013) indicates that phengite-bearing restites left from incipient melting of metasediments at high pressures have high Nb/Ta ratios. Large grains of phengite do occur in the quartzite of our study (Fig. 2c), indicating new growth of phengite during

the exhumation. However, the trace element compositions of phengite megacrystals analyzed by LA-ICPMS show very low contents of Nb and Ta, mostly below the detection limit (Table 2). In this regard, the large phengite grains are not a residual phase after metamorphic dehydration during the exhumation and thus of secondary origin. The primary phengite would have been broken down to produce the aqueous solution and hydrous melt. As such, the second mechanism is responsible for the Nb/Ta variation in the megacrystal rutile. In other words, the rutile rims would have crystallized from a kind of geofluids that has high contents of Nb, Ta, Sb and W. It is known that there are three types of geofluids in subduction zones, i.e., aqueous solution, hydrous melt and supercritical fluid, which exhibit different capacities in dissolving and transporting trace elements (Hermann et al., 2006; Zheng et al., 2011b). Generally, water-soluble incompatible trace element such as LILE are mobile in the aqueous solution; water-insoluble incompatible trace elements such as LREE and MREE can be dissolved and transported together with LILE by the hydrous melt; eventually all usually fluid-immobile incompatible trace elements such as HREE and HFSE can be dissolved and transported by the supercritical fluid under subduction-zone UHP metamorphic conditions (Tatsumi and Nakamura, 1986; Brenan et al., 1995; Kogiso et al., 1997; Arculus et al., 1999; Becker et al., 2000; Scambelluri et al., 2001; John

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

21

Fig. 11. Diagram of rutile Zr isopleths as a function of both temperature and pressure (calculated after the experimental calibration of Tomkins et al., 2007). Diamond denotes the Zr-in-rutile temperatures for UHP quartzite in the Sulu orogen. The pressure was assumed from possible P–T–t path of UHP slices in this region.

et al., 2004; Kessel et al., 2005; Hermann et al., 2006;Xia et al., 2010; Hayden and Manning, 2011; Zheng et al., 2011b). The significant enrichment of HFSE in the rutile rims suggests that the geofluid could have the property of supercritical fluid. However, the rutile rims would not be able to have crystallized directly from the supercritical fluid because of its great capacity in dissolving various elements. Instead, it would precipitate from its derivative, i.e. the product of its phase separation into aqueous solution and hydrous melt at declined pressures. This is consistent with the finding of highly cuspate feldspars in grain boundaries of the UHP quartzite (Chen et al., 2013a; this study), indicating the former occurrence of hydrous melt. The peak metamorphic pressure for the Qinglongshan eclogite would exceed 3.5 GPa at 650–700 °C (e.g., Zhang et al., 2005, 2009; Xu et al., 2006), which concurs with our P–T estimate for the coexisting UHP quartzite. The occurrence of phengite metacrystals with high SiO2 contents (Si = 3.57–3.66 pfu at O = 11) in the quartzite indicates that the geofluid would have been generated still at the UHP conditions. At such a high pressure, the supercritical fluid is likely to occur in the metamorphic rocks of felsic composition (Hermann et al., 2006; Zheng et al., 2011b). Substantially, the existence of such supercritical UHP fluid has been documented by the study of MS inclusions in UHP eclogite and kyanite quartzite from Hushan close to Qinglongshan (Ferrando et al., 2005; Frezzotti et al., 2007) as well as UHP eclogite and vein at Chizhuang in Donghai county (Zhang et al., 2008). In this regard, the supercritical fluid would be regionally generated in the Donghai slice of the Sulu UHP terrane. 6. IMPLICATIONS FOR NB/TA FRACTIONATION DURING METAMORPHIC DEHYDRATION The occurrence of newly grown rutile and zircon in the UHP quartzite provides mineralogical evidence for the

local sinking of refractory HFSE by the special property of geofluids during subduction-zone metamorphism. This is consistent with experimental data for the solubility of these two accessory minerals in aqueous solution, hydrous melt and supercritical fluid (e.g., Tropper and Manning, 2005; Gaetani et al., 2008; Manning et al., 2008; Rapp et al., 2010; Hayden and Manning, 2011; Mysen, 2012; Wilke et al., 2012; Bernini et al., 2013). As a result, water-insoluble HFSE become fluid-mobile trace elements under subduction-zone UHP metamorphic conditions. Although partial melting of the subducting crust is not able to mobilize HFSE at subarc depths of 80–130 km, it facilitates the formation of supercritical fluids at further elevated pressures and temperatures (Zheng et al., 2011b). This would favor the dissolution of crustally derived rutile (including other Ti-bearing phases) and zircon and thus the transport of HFSE by the supercritical fluid. Therefore, the effectiveness of HFSE uptake and transport in deep subduction zones is primarily controlled by the property and composition of geofluids. Niobium and Ta have the same oxidation state and nearly identical ionic radii (Shannon, 1976; Tiepolo et al., 2000; Meinhold, 2010) and thus would remain tightly coupled during geochemical processes in the crust-mantle differentiation system. However, there is a significant difference in their mass, which may be a potential cause for Nb/Ta differentiation during geochemical processes. It is known that average Nb/Ta ratios are 12–13 for the continental crust (Rudnick and Gao, 2003), 15.5 for the depleted mantle (Jochum et al., 2000; Workman and Hart, 2005), 14.2 for mid-ocean ridge basalts (Mu¨nker et al., 2003), 15.9 for ocean island basalts (Pfa¨nder et al., 2007) and 17.5–19.9 for the primitive mantle (McDonough and Sun, 1995; Mu¨nker et al., 2003). In general, these differences have been used to argue for geochemical fractionation between Nb and Ta during extraction of the continental crust by partial melting from the primitive

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

22

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

mantle at oceanic subduction zone (e.g., Rudnick et al., 2000; Foley et al., 2002; Rapp et al., 2003; Xiao et al., 2006; Liang et al., 2009; Zheng et al., 2011b; Ding et al., 2013). However, less attention has been paid to the effect of metamorphic dehydration on the Nb/Ta fractionation during subduction-zone metamorphism. Based on the laser analysis of Nb and Ta concentrations across large rutile grains from UHP eclogite and its enclosed quartz vein in the Sulu orogen, Xiao et al. (2006) observed that rutile cores exhibit consistently lower Nb/Ta ratios than the continental crust, whereas rutile rims exhibit significant variations and elevations in Nb/Ta ratios with a decrease of Ta contents. The authors interpreted such intragrain Nb/Ta variations as suggesting major Nb/ Ta fractionation during prograde subduction of the continental crust from blueschist-facies to amphibole eclogite-facies in the absence of rutile. Brenan et al. (1994) experimentally determined HFSE partitioning coefficients between rutile and aqueous fluid, obtaining Nb/Ta partition coefficients (DNb/Ta) > 1.0 in the presence of residual rutile. This would yield high Nb/Ta ratios for rutile in the residual eclogite, in contrast to the low Nb/Ta cores analyzed by Xiao et al. (2006). On the other hand, the increase in Nb/Ta ratios for rutile rims can be explained by the experimental Nb/Ta partition results of Brenan et al. (1994), but it remains enigmatic why they are associated with the decrease of Ta contents. For this reason, Zheng et al. (2011a) hypothesized that the intragrain variations of rutile Nb/Ta ratios are dictated by the property of geofluids during subduction-zone metamorphism. In detail, the low Nb/Ta ratios for cores are ascribed to rutile growth from mineralogical reactions in association with eclogitefacies metamorphic dehydration in the presence of rutile residues during prograde subduction, whereas the high Nb/Ta ratios for rims are ascribed to rutile growth from the aqueous solution that is the phase separated product of supercritical fluid during retrograde exhumation. The profile analyses of rutile Nb/Ta ratios for core and rim in the present study allow for testing of this hypothesis. The rims of the megacrystal rutile from the UHP quartzite in the Sulu orogen generally show higher Nb/Ta ratios than the cores (Fig. 9 and Table 6). As illustrated in Fig. 9, the increase in Nb/Ta ratios is primarily caused by a significant increase in Nb contents. In particular, the Nb/Ta ratios of 19.4–29.6 for our metamorphic rutile are higher than the chondritic Nb/Ta ratios of 17.5–19.9. This suggests that the rutile would have precipitated from high Nb/Ta geofluids. The experimental study of Stepanov and Hermann (2013) indicates that phengite and biotite in metamorphic rocks preferentially incorporate Nb over Ta. As such, the aqueous solution of high Nb/Ta ratios can be derived from metamorphic dehydration due to the breakdown of phengite/biotite during the exhumation of deeply subducted continental crust. On the other hand, the association of high Nb/Ta ratios with the decreased Ta contents can be ascribed to the effect of partial melting on the rutile Nb/Ta differentiation (Schmidt et al., 2004; Xiong et al., 2011). Available analyses exhibit contrasting variations in Nb/ Ta ratios for rutile from UHP eclogites and enclosed quartz veins elsewhere in the Dabie-Sulu orogenic belt. While

suprachondritic Nb/Ta ratios occur in rutile from some UHP eclogites and enclosed quartz veins (Xiao et al., 2006; Zheng et al., 2011a; this study), subchondritic Nb/ Ta ratios occur in rutile from other eclogites and enclosed quartz veins (Xiao et al., 2006; Huang et al., 2012). In this regard, there may be a significant difference in the geochemical behavior of Nb/Ta fractionation between metamorphic dehydration during prograde subduction and retrograde exhumation, respectively. This difference is probably due to mineralogical controls of the Nb and Ta budget during the prograde and retrograde dehydration. While rutile dominates the Nb and Ta budget during eclogite-facies dehydration in the one case (Zack et al., 2002; Schmidt et al., 2009), amphibole dominates such budget during amphibolite-facies hydration in the other case (Foley et al., 2002). It is known that rutile has DNb/Ta > 1.0 (Brenan et al., 1994; Stalder et al., 1998; Green and Adam, 2003; Xiong et al., 2005). Thus, the Nb/Ta fractionation by eclogite-facies metamorphic dehydration and partial melting in the case of rutile residues during prograde subduction is capable of resulting in the subchondritic Nb/Ta ratios for the continental crust (Foley et al., 2000; Rudnick et al., 2000). On the other hand, Mg-poor amphibole has DNb/Ta > 1.0 (Tiepolo et al., 2000). As a consequence, the metamorphic transformation from amphibolite to eclogite during subduction would release the aqueous solutions of high Nb/Ta ratios, leading to the precipitation of high Na/Ta rutile from such geofluids. Although experimental studies of Nb and Ta partitioning between rutile and fluid/melt usually give DNb/Ta > 1.0 (Brenan et al., 1994; Stalder et al., 1998; Green and Adam, 2003; Xiong et al., 2005), the melting experiments of Xiong et al. (2011) give different results. While their dehydration melting experiments yield DNb/Ta > 1.0 for water-undersaturated melts, their hydration melting experiments give DNb/Ta < 1.0 for water-saturated melts. The experimental study of Schmidt et al. (2004) also indicates that rutile preferentially incorporates Ta over Nb during dehydration melting. As such, locally water-saturated melting is capable of generating hydrous melts, from which crystallized rutile domains tend to exhibit low Nb/Ta ratios with decreased Nb contents. Therefore, the difference in the behavior of Nb/Ta fractionation dictates the compatibilities of Nb and Ta in rutile during its growth from different properties of geofluids. This may be a basic cause for the Nb/Ta fractionation during metamorphic dehydration and partial melting at subduction zones. On the other hand, hydrous minerals such as amphibole, biotite and phengite preferentially incorporate Nb over Ta (Tiepolo et al., 2000; Stepanov and Hermann, 2013). Thus, their breakdown generates high Nb/Ta geofluids from which high Nb/Ta rutile is precipitated. In either case, geofluids released from the exhumation dehydration of UHP eclogite-facies rocks tend to exhibit suprachondritic Nb/Ta ratios, whereas subchondritic Nb/Ta rutile would be produced if its growth is caused by subduction dehydration at eclogite-facies conditions. Previous studies suggest that the supercritical fluid has the high solubility of various fluid-immobile incompatible trace elements including HREE and HFSE (Kessel et al.,

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

2005; Xia et al., 2010; Hayden and Manning, 2011; Zheng et al., 2011b) and the high capacity to extract HFSE such as Nb, Ta and Ti from Ti-bearing phases (such as rutile) in metamorphic rocks. In addition, the supercritical fluid favors Nb over Ta (Kessel et al., 2005) and thus has relatively high Nb/Ta ratios. Therefore, the high Nb/Ta ratios with increase Nb contents in the rims of megacrystal rutile (Fig. 9) can be related to either the breakdown of phengite/ biotite in the UHP metamorphic rocks or the involvement of supercritical fluid that acquired high Nb and Ta concentrations due to the metamorphic dehydration still at UHP conditions (Zheng et al., 2011b). Nevertheless, the aqueous HFSE-rich solution for the rutile overgrowth would have derived from the phase separation of supercritical fluid during the retrograde exhumation rather than from the supercritical fluid itself during the peak UHP metamorphism. This conclusion is consistent with the above argument for the trace element partitioning in rutile, in which the enrichment of Nb, Ta, Sb and W in the rim is ascribed to the rutile overgrowth from the phase separated product of supercritical fluid. As soon as TiO2 achieves local oversaturation in the aqueous solution, rutile precipitates together with silica to form the quartzite. This differs from the immiscible experiments of Green and Adam (2003) on trace element partitioning between aqueous fluid and hydrous melt, which showed that at conditions of 650–700 °C at 3.0 GPa, significant amounts of LILE and Sr enter the aqueous fluid whereas REE, Th, U and HFSE are nearly completely retained in the solid phase quenched from the melt. 7. CONCLUSIONS The laser ablation U–Pb dating of rutile yields a concordant age of 205.2 ± 1.6 Ma for UHP quartzite in the Sulu orogen. It is significantly younger than the laser ablation U–Pb zircon ages of 223 ± 3 Ma for the second episode of zircon growth during the exhumation of deeply subducted continental crust. The laser analyses of trace elements in rutile and zircon suggest that the two accessory minerals were grown from metamorphic fluids. Because the closure temperatures of 600–650 °C for Pb diffusion in rutile are similar to the Zr-in-rutile temperatures of 600–640 °C for rutile growth, we interpret the rutile U–Pb age as dating the rapid closure of radiogenic Pb diffusion in the rutile subsequent to its growth during the exhumation. Trace element analyses of core-rim profiles for large rutile grains provide geochemical constraints on the property of metamorphic fluid. The significant enrichment of Nb, Ta, Sb and W in rutile rims suggests local enrichment of these water-insoluble incompatible trace elements in metamorphic fluid, which may be the product of phase separation from a supercritical fluid during the exhumation. The trace element composition of metamorphic fluid is recorded by the rutile of different generations in UHP metamorphic rocks. Geofluids released from the exhumation dehydration of UHP eclogite-facies rocks tend to exhibit suprachondritic Nb/Ta ratios, whereas low Nb/Ta rutile would be generated if its growth is associated with prograde eclogite-facies metamorphism during subduction.

23

ACKNOWLEDGMENTS This study was supported by funds from the Natural Science Foundation of China (41173046 and 41221062). Thank are due to R.-X. Chen, B.-H. Ding and W.-C. Li for their assistance with the field sampling, to J. Xu and M. Feng for their assistance with the electron microprobe analysis, to Z.C. Hu for his assistance with the LA-ICPMS zircon U–Pb dating and the trace element analyses of rutile and zircon. Comments by three anonymous reviewers, associate editor Weidong Sun and guest editor Fangzhen Teng have greatly helped improvement of the presentation.

REFERENCES Ague J. J., Eckert J. O., Chu X., Baxter E. F. and Chamberlain C. P. (2013) Discovery of ultrahigh-temperature metamorphism in the Acadian orogen, Connecticut, USA. Geology 41, 271–274. Andersen T. (2002) Correction of common lead in U–Pb analyses that do not report 204Pb. Chem. Geol. 192, 59–79. Arculus R. J., Lapierre H. and Jaillard E. (1999) Geochemical window into subduction and accretion processes: Raspas metamorphic complex Ecuador. Geology 27, 547–550. Aulbach S., O’Reilly S. Y., Griffin W. L. and Pearson N. J. (2008) Subcontinental lithospheric mantle origin of high niobium/ tantalum ratios in eclogites. Nat. Geosci. 1, 458–472. Baldwin J. A., Brown M. and Schmitz M. D. (2007) First application of titanium-in-zircon thermometry to ultrahightemperature metamorphism. Geology 35, 295–298. Becker H., Jochum K. P. and Carlson R. W. (2000) Trace element fractionation during dehydration of eclogites from highpressure terranes and the implications for element fluxes in subduction zones. Chem. Geol. 163, 65–99. Bernini D., Audetat A., Dolejs D. and Keppler H. (2013) Zircon solubility in aqueous fluids at high temperatures and pressures. Geochim. Cosmochim. Acta 119, 178–187. Bibikova E., Skiold T., Bogdanova S., Gorbatschev R. and Slabunov A. (2001) Titanite-rutile thermochronometry across the boundary between the Archaean Craton in Karelia and the Belomorian Mobile Belt, eastern Baltic Shield. Precambrian Res. 105, 315–330. Bracciali L., Parrish R. R., Horstwood M. S. A., Condon D. J. and Najman Y. (2013) U–Pb LA-(MC)-ICP-MS dating of rutile: new reference materials and applications to sedimentary provenance. Chem. Geol. 347, 82–101. Brenan J. M., Shaw H. F., Phinney D. L. and Ryerson F. J. (1994) Rutile-aqueous fluid partitioning of Nb, Ta, Hf, Zr, U and Th: implications for high field strength element depletions in islandarc basalts. Earth Planet. Sci. Lett. 128, 327–339. Brenan J. M., Shaw H. F., Ryerson F. J. and Phinney D. L. (1995) Mineral-aqueous fluid partitioning of trace elements at 900 °C and 2.0 GPa: constraints on the trace element chemistry of mantle and deep crustal fluids. Geochim. Cosmochim. Acta 59, 3331–3350. Bromiley G. D. and Redfern S. A. T. (2008) The role of TiO2 phases during melting of subduction-modified crust: implications for deep mantle melting. Earth Planet. Sci. Lett. 267, 301– 308. Carswell D. A. and Compagnoni R. (2003) Ultra-high pressure metamorphism. EMU Notes in Mineralogy 5, 1–508. Chen R.-X., Zheng Y.-F., Zhao Z.-F., Tang J., Wu F. Y. and Liu X. C. (2007) Zircon U–Pb age and Hf isotope evidence for contrasting origin of bimodal protoliths for ultrahigh-pressure metamorphic rocks from the Chinese Continental Scientific Drilling project. J. Metamorph. Geol. 25(8), 873–894.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

24

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Chen R.-X., Zheng Y.-F. and Xie L. W. (2010) Metamorphic growth and recrystallization of zircon: distinction by simultaneous in-situ analyses of trace elements, U–Th–Pb and Lu–Hf isotopes in zircons from eclogite-facies rocks in the Sulu orogen. Lithos 114, 132–154. Chen Y.-X., Zheng Y.-F., Chen R.-X., Zhang S.-B., Li Q.-L., Dai M.-N. and Chen L. (2011) Metamorphic growth and recrystallization of zircons in extremely 18O-depleted rocks during eclogite-facies metamorphism: evidence from U–Pb ages, trace elements, and O–Hf isotopes. Geochim. Cosmochim. Acta 75, 4877–4898. Chen R.-X., Zheng Y.-F. and Hu Z. C. (2012) Episodic fluid action during exhumation of deeply subducted continental crust: geochemical constraints from zoisite–quartz vein and host metabasite in the Dabie orogen. Lithos 155, 146–166. Chen Y.-X., Zheng Y.-F. and Hu Z. C. (2013a) Petrological and zircon evidence for anatexis of UHP quartzite during continental collision in the Sulu orogen. J. Metamorph. Geol. 31, 389–413. Chen Y.-X., Zheng Y.-F. and Hu Z. C. (2013b) Synexhumation anatexis of ultrahigh-pressure metamorphic rocks: petrological evidence from granitic gneiss in the Sulu orogen. Lithos 156– 159, 69–96. Chen Y.-X., Zheng Y.-F., Li L. and Chen R.-X. (2014) Fluid–rock interaction and geochemical transport during protolith emplacement and continental collision: a tale from Qinglongshan ultrahigh-pressure metamorphic rocks in the Sulu orogen. Am. J. Sci. 314, 357–399. Chen Z. Y. and Li Q. L. (2008) Zr-in-rutile thermometry in eclogite at Jinheqiao in the Dabie orogen and its geochemical implications. Chin. Sci. Bull. 53, 768–776. Cherniak D. J. (2000) Pb diffusion in rutile. Contrib. Mineral. Petrol. 139, 198–207. Cherniak D. J., Mancheste J. and Watson E. B. (2007) Zr and Hf diffusion in rutile. Earth Planet. Sci. Lett. 261, 267–279. Christofell C. A., Connelly J. N. and Ahall K. L. (1999) Timing and characterization of recurrent pre-Sveconorwegian metamorphism and deformation in the Varberg–Halmstad region of SW Sweden. Precambrian Res. 98, 173–195. Cong B. L. (1996) Ultrahigh-Pressure Metamorphic Rocks in the Dabieshan-Sulu Region of China. Science Press, Beijing, 224 pp. Connelly J. N., Van Goo J. A. M. and Mengel F. C. (2000) Temporal evolution of a deeply eroded orogen: the Nagssugtoqidian orogen, West Greenland. Can. J. Earth Sci. 37, 1121–1142. Corfu F. and Andrews A. J. (1986) A U–Pb age for mineralized Nipissing diabase, Gowganda, Ontario. Can. J. Earth Sci. 23, 107–109. Corfu F. and Easton R. M. (1995) U–Pb geochronology of the Mazinaw terrane, an imbricate segment of the Central metasedimentary belt, Grenville province, Ontario. Can. J. Earth Sci. 32, 959–976. Cox R. A., Dunning G. R. and Indares A. (1998) Petrology and U– Pb geochronology of mafic, high-pressure, metamorphic coronites from the Tshenukutish domain, eastern Grenville province. Precambrian Res. 90, 59–83. Cox R. A., Indares A. and Dunning G. R. (2002) Temperature– time paths in the high-P Manicouagan imbricate zone, eastern Grenville province: evidence for two metamorphic events. Precambrian Res. 117, 225–250. Deer W. A., Howie R. A. and Zussman J. (1992) An Introduction to Rock-Forming Minerals, second ed. Longman Group Ltd., Harlow, UK, 712 pp. Dodson M. H. (1973) Closure temperature in cooling geochronological and petrological systems. Contrib. Mineral. Petrol. 40, 259–274.

Ding X., Lundstrom C., Huang F., Li J., Zhang Z. M., Sun X. M., Liang J. L. and Sun W. D. (2009) Natural and experimental constraints on formation of the continental crust based on niobium-tantalum fractionation. Intern. Geol. Rev. 51, 473–501. Ding X., Hu Y. H., Zhang H., Li C. Y., Ling M. X. and Sun W. D. (2013) Major Nb/Ta fractionation recorded in garnet amphibolite facies metagabbro. J. Geol. 121, 255–274. Enami M., Zang Q. and Yin Y. (1993) High-pressure eclogites in northern Jiangsu-southern Sangdong province, eastern China. J. Metamorph. Geol. 11, 589–603. Ernst W. G., Tsujimori T., Zhang R. Y. and Liou J. G. (2007) Permo-Triassic collision, subduction-zone metamorphism, and tectonic exhumation along the East Asian continental margin. Annu. Rev. Earth Planet. Sci. 35, 73–110. Ewing T. A., Herman J. and Rubatto D. (2013) The robustness of the Zr-in-rutile and Ti-in-zircon thermometers during hightemperature metamorphism (Ivrea-Verbano zone, northern Italy). Contrib. Mineral. Petrol. 165, 757–779. Ferrando S., Frezzotti M. L., Dallai L. and Compagnoni R. (2005) Multiphase solid inclusions in UHP rocks (Su-Lu, China): remnants of supercritical silicate-rich aqueous fluids released during continental subduction. Chem. Geol. 223, 68–81. Ferry J. M. and Watson E. B. (2007) New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers. Contrib. Mineral. Petrol. 154, 429–437. Foley S., Tiepolo M. and Vannucci R. (2002) Growth of early continental crust controlled by melting of amphibolite in subduction zones. Nature 417, 837–840. Foley S. F., Barth M. G. and Jenner G. A. (2000) Rutile/melt partition coefficients for trace elements and assessment of the influence of rutile on the trace element characteristics of subduction zone magmas. Geochim. Cosmochim. Acta 64, 933–938. Frezzotti M. L., Ferrando S., Dallai L. and Compagnoni R. (2007) Intermediate alkali-alumino-silicate aqueous solutions released by deeply subducted continental crust: fluid evolution in UHP OH-rich topaz-kyanite quartzites from Donghai (Sulu, China). J. Petrol. 48, 1219–1241. Gaetani G. A., Asimow P. D. and Stolper E. M. (2008) A model for rutile saturation in silicate melts with applications to eclogite partial melting in subduction zones and mantle plumes. Earth Planet. Sci. Lett. 272, 720–729. Gao X.-Y., Zheng Y.-F. and Chen Y.-X. (2011) U–Pb ages and trace elements in metamorphic zircon and titanite from UHP eclogite in the Dabie orogen: constraints on P–T–t path. J. Metamorph. Geol. 29, 721–740. Graham J. and Morris R. C. (1973) Tungsten- and antimonysubstituted rutile. Mineral. Mag. 39, 470–473. Green T. H. (1995) Significance of Nb/Ta as an indicator of geochemical processes in the crust–mantle system. Chem. Geol. 120, 347–359. Green T. H. and Adam J. (2003) Experimentally-determined trace element characteristics of aqueous fluid from partially dehydrated mafic oceanic crust at 3.0 GPa, 650–700 °C. Eur. J. Mineral. 15, 815–830. Haggerty S. E. (1991) Oxide mineralogy of the upper mantle. Rev. Mineral. Geochem. 25, 355–416. Hayden L. A. and Manning C. E. (2011) Rutile solubility in supercritical NaAlSi3O8–H2O fluids. Chem. Geol. 284, 74–81. Hermann J. and Spandler C. J. (2008) Sediment melts at sub-arc depths: an experimental study. J. Petrol. 49, 717–740. Hermann J., Spandler C., Hack A. and Korsakov A. (2006) Aqueous fluids and hydrous melts in high-pressure and ultrahigh pressure rocks: implications for element transfer in subduction zones. Lithos 92, 399–417.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx Hirajima T., Ishiwateri A., Cong B. L., Zhang R. Y., Banno S. and Nozaka T. (1990) Identification of coesite in Mengzhong eclogite from Donghai county, northeastern Jiangsu province, China. Mineral. Mag. 54, 579–584. Hirdes W. and Davis D. W. (2002) U–Pb zircon and rutile metamorphic ages of Dahomeyan garnet-hornblende gneiss in southeastern Ghana, West Africa. J. Afr. Earth Sci. 35, 445– 449. Horstwood M. S. A., Foster G. L., Parrish R. R., Noble S. R. and Nowell G. M. (2003) Common-Pb corrected in situ U–Pb accessory mineral geochronology by LA-MC-ICP-MS. J. Anal. At. Spectrom. 18, 837–846. Huang J., Xiao Y. L., Gao Y. J., Hou Z. H. and Wu W. (2012) Nb– Ta fractionation induced by fluid-rock interaction in subduction-zones: constraints from UHP eclogite- and vein-hosted rutile from the Dabie orogen, Central-Eastern China. J. Metamorph. Geol. 30, 821–842. Jackson S. E., Pearson N. J., Griffin W. L. and Belousova E. A. (2004) The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U–Pb zircon geochronology. Chem. Geol. 211, 47–69. Jochum K. P., Stolz A. J. and Mcorist G. (2000) Niobium and tantalum in carbonaceous chondrites: constraints on the solar system and primitive mantle niobium/tantalum, zirconium/ niobium, and niobium/uranium ratios. Meteorit. Planet. Sci. 35, 229–235. John T., Scherer E. E., Haase K. and Schenk V. (2004) Trace element fractionation during fluid-induced eclogitization in a subducting slab: trace element and Lu-Hf-Sm-Nd isotope systematics. Earth Planet. Sci. Lett. 227, 441–456. Kalfoun F., Ionov D. and Merlet C. (2002) HFSE residence and Nb/Ta ratios in metasomatised, rutile-bearing mantle peridotites. Earth Planet. Sci. Lett. 199, 49–65. Kamber B. S. and Collerson K. D. (2000) Role of “hidden” deeply subducted slabs in mantle depletion. Chem. Geol. 166, 241–254. Kamber F., Ionov D. and Merlet C. (2002) HFSE residence and Nb/Ta ratios in metasomatised, rutile-bearing mantle peridotites. Earth Planet. Sci. Lett. 199, 49–65. Kessel R., Schmidt M. W., Ulmer P. and Pettke T. (2005) Trace element signature of subduction-zone fluids, melts and supercritical liquids at 120–180 km depth. Nature 437, 724–727. Klemme S., Blundy J. D. and Wood B. J. (2002) Experimental constraints on major and trace element partitioning during partial melting of eclogite. Geochim. Cosmochim. Acta 66, 3109– 3123. Kogiso T., Tatsumi Y. and Nakano S. (1997) Trace element transport during dehydration processes in the subducted oceanic crust: 1. Experiments and implications for the origin of ocean island basalt. Earth Planet. Sci. Lett. 148, 193–205. Kohn M. J. (2003) Geochemical zoning in metamorphic minerals. Treatise on Geochemitry. 3, 229–261. Kooijman E., Mezger K. and Berndt J. (2010) Constraints on the U–Pb systematics of metamorphic rutile from in situ LA-ICPMS analysis. Earth Planet. Sci. Lett. 293, 321–330. Kooijman E., Smit M. A., Mezger K. and Berndt J. (2012) Trace element systematics in granulite facies rutile: implications for Zr geothermometry and provenance studies. J. Metamorph. Geol. 30, 397–412. Lang H. M. and Gilotti J. A. (2007) Partial melting of metapelites at ultrahigh-pressure conditions, Greenland Caledonides. J. Metamorph. Geol. 25, 129–147. Li Q. L., Li S. G., Zheng Y.-F., Li H., Massonne H. J. and Wang Q. (2003) A high precision U–Pb age of metamorphic rutile in coesite-bearing eclogite from the Dabie mountains in central China: a new constraint on the cooling history. Chem. Geol. 200, 255–265.

25

Li S. G., Jagoutz E., Lo C. H., Chen Y., Li Q. and Xiao Y. (1999) Sm/Nd, Rb/Sr and 40Ar/39Ar isotopic systematic of the ultrahigh-pressure metamorphic rocks in the Dabie-Sulu belt, central China: a retrospective view. Int. Geol. Rev. 41, 1114– 1124. Li Q. L., Lin W., Sun W., Li X. H., Shi Y. H., Liu Y. and Tang G. Q. (2011) SIMS U–Pb rutile age of low-temperature eclogites from southwestern Chinese Tianshan, NW China. Lithos 122, 76–86. Li W.-C., Chen R.-X., Zheng Y.-F., Li Q. L. and Hu Z. C. (2013) Zirconological tracing of transition between aqueous fluid and hydrous melt in the crust: constraints from pegmatite vein and host gneiss in the Sulu orogen. Lithos 162–163, 157–174. Liang J. L., Ding X., Sun X. M., Zhang Z. M., Zhang H. and Sun W. D. (2009) Nb/Ta fractionation observed in eclogites from the Chinese Continental Scientific Drilling project. Chem. Geol. 268, 27–40. Liou J. G., Zhang R. Y., Eide E. A., Wang X. M., Ernst W. G. and Maruyama S. (1996) Metamorphism and tectonics of highpressure and ultra-high-pressure belts in the Dabie Sulu region, China. In The Tectonics of Asia (eds. M. T. Harrison and A. Yin). Cambridge University Press, Cambridge, pp. 300–344. Liou J. G., Zhang R. Y. and Jahn B.-M. (1997) Petrology, geochemistry and isotope data on an ultrahigh-pressure jadeite quartzite from Shuanghe, Dabie Mountains, East-central China. Lithos 41, 59–78. Liou J. G., Ernst W. G., Zhang R. Y., Tsujimori T. and Jahn J. G. (2009) Ultrahigh-pressure minerals and metamorphic terranes – the view from China. J. Asian Earth Sci. 35, 199–231. Liu F. L. and Liou J. G. (2011) Zircon as the best mineral for P–T– time history of UHP metamorphism: a review on mineral inclusions and U–Pb SHRIMP ages of zircons from the DabieSulu UHP rocks. J. Asian Earth Sci. 40, 1–39. Liu F. L., Xu Z. Q. and Liou J. G. (2004) Tracing the boundary between UHP and HP metamorphic belts in the southwestern Sulu Terrane, eastern China: evidence from mineral inclusions in zircons from metamorphic rocks. Int. Geol. Rev. 46, 409–425. Liu D. Y., Jian P., Kro¨ner A. and Xu S. T. (2006) Dating of prograde metamorphic events deciphered from episodic zircon growth in rocks of the Dabie-Sulu UHP complex, China. Earth Planet. Sci. Lett. 250, 650–666. Liu Y. S., Hu Z. C., Gao S., Gu¨nther D., Xu J., Gao C. G. and Chen H. H. (2008) In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard. Chem. Geol. 257, 34–43. Liu Y. S., Gao S., Hu Z. C., Gao C., Zong K. and Wang D. (2010) Continental and oceanic crust recycling-induced melt–peridotite interactions in the Trans-North China Orogen: U–Pb dating, Hf isotopes and trace elements in zircons from mantle xenoliths. J. Petrol. 51, 537–571. Ludwig K. R. (2003) User’s Manual for Isoplot 3.00: A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication, No. 4, Berkeley, 70 pp. Luvizotto G. L., Zack T., Meyer H. P., Ludwig T., Triebold S., Kronz A., Munker C., Stockli D. F., Prowatke S., Klemme S., Jacob D. E. and Eynatten H. (2009) Rutile crystals as potential trace element and isotope mineral standards for microanalysis. Chem. Geol. 261, 346–369. Manning C. E., Wilke M., Schmidt C. and Cauzid J. (2008) Rutile solubility in albite-H2O and Na2Si3O7-H2O at high temperatures and pressures by in-situ synchrotron radiation microXRF. Earth Planet. Sci. Lett. 272, 730–737. Marschall H. R., Dohmen R. and Ludwig T. (2013) Diffusioninduced fractionation of niobium and tantalum during continental crust formation. Earth Planet. Sci. Lett. 375, 361–371.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

26

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

McDonough W. F. (1991) Partial melting of subducted oceanic crust and isolation of its residual eclogitic lithology. Philos. Trans. R. Soc. A335, 407–418. McDonough W. F. and Sun S.-S. (1995) The composition of the Earth. Chem. Geol. 120, 223–253. Meinhold G. (2010) Rutile and its applications in earth sciences. Earth Sci. Rev. 102, 1–28. Mezger K., Hanson G. N. and Bohlen S. R. (1989) High-precision U–Pb ages of metamorphic rutiles: application to the cooling history of high-grade terranes. Earth Planet. Sci. Lett. 96, 106– 118. Mezger K., Rawnsley C., Bohlen S. R. and Hanson G. N. (1991) U–Pb garnet, sphene, monazite, and rutile ages: implications for the duration of high-grade metamorphism and cooling histories Adirondack Mountains, New York. J. Geol. 99, 415– 428. Miller C., Zanetti A. and Tho¨ni M. (2007) Eclogitisation of gabbroic rocks: Redistribution of trace elements and Zr in rutile thermometry in an Eo-Alpine subduction zone (Eastern Alps). Chem. Geol. 239, 96–123. Mu¨ller W., Shelley M., Miller P. and Broude S. (2009) Initial performance metrics of a new custom-designed ArFexcimer LA-ICPMS system coupled to a two-volume laser-ablation cell. J. Anal. At. Spectrom. 24, 209–214. Mu¨nker C., Pfa¨nder J. A., Weyer S., Bu¨chl A., Kleine T. and Mezger K. (2003) Evolution of planetary cores and the erath-moon system from Nb/Ta systematics. Science 301, 84– 87. Mysen B. (2012) High-pressure and high-temperature titanium solution mechanisms in silicate-saturated aqueous fluids and hydrous silicate melts. Am. Mineral. 87, 1241–1251. Nebel O., van Westrenen W., Vronn P. Z., Wille M. and Raith M. M. (2010) Deep mantle storage of the Earth’s missing niobium in late-stage residual melts from a magma ocean. Geochim. Cosmochim. Acta 74, 4392–4404. Norcross C., Davi D. W., Spooner E. T. C. and Rust A. (2000) U– Pb and Pb–Pb age constraints on Paleoproterozoic magmatism, deformation and gold mineralization in the Omai area, Guyana Shield. Precambrian Res. 102, 69–86. Pfa¨nder J. A., Muenker C., Stracke A. and Mezger K. (2007) Nb/ Ta and Zr/Hf in ocean island basalts – implications for crust– mantle differentiation and the fate of Niobium. Earth Planet. Sci. Lett. 254, 158–172. Pfa¨nder J. A., Jung S., Muenker C., Stracke A. and Mezger K. (2012) A possible high Nb/Ta reservoir in the continental lithospheric mantle and consequences on the global Nb budget – evidence from continental basalts from Central Germany. Geochim. Cosmochim. Acta 77, 232–251. Rapp R. P., Shimizu N. and Norman M. D. (2003) Growth of early continental crust by partial melting of eclogite. Nature 425, 605–609. Rapp J. F., Klemme S., Butler I. B. and Harley S. L. (2010) Extremely high solubility of rutile in chloride and fluoridebearing metamorphic fluids: an experimental investigation. Geology 38, 323–326. Rice C., Darke K. and Still J. (1998) Tungsten-bearing rutile from the Kori Kollo gold mine Bolı´via. Mineral. Mag. 62, 421–429. Richards J. P., Krogh T. E. and Spooner E. T. C. (1988) Fluid inclusion characteristics and U–Pb rutile age of late hydrothermal alteration and veining at the Musoshi stratiform copper deposit, Central African copper belt, Zaire. Econ. Geol. 83, 118– 139. Rubatto D. (2002) Zircon trace element geochemistry: partitioning with garnet and the link between U–Pb ages and metamorphism. Chem. Geol. 184, 123–138.

Rubatto D. and Hermann J. (2007) Experimental zircon/melt and zircon/garnet trace element partitioning and implications for the geochronology of crustal rocks. Chem. Geol. 241, 38–61. Rudnick R. L. and Gao S. (2003) Composition of the continental crust. Treatise on Geochemistry 3, 1–64. Rudnick R. L., Barth M., Horn I. and McDonough W. F. (2000) Rutile-bearing refractory eclogites: missing link between continents and depleted mantle. Science 287, 278–281. Saunders A. D., Tarney J. and Weaver S. D. (1980) Transverse geochemical variations across the Antarctic Peninsula: implications for the genesis of calc-alkaline magmas. Earth Planet. Sci. Lett. 46, 344–360. Scambelluri M., Bottazzi P., Trommsdorff V., Vannucci R., Hermann J., Gomez-Pugnaire M. T. and Lopez-SanchezVizcaino V. (2001) Incompatible element-rich fluids released by antigorite breakdown in deeply subducted mantle. Earth Planet. Sci. Lett. 192, 457–470. Scha¨rer U., Krogh T. E. and Gower C. F. (1986) Age and evolution of the Grenville province in eastern Labrador from U–Pb systematics of accessory minerals. Contrib. Mineral. Petrol. 94, 438–451. Schmidt M. W., Dardon A., Chazot G. and Vannucci R. (2004) The dependence of Nb and Ta rutile-melt partitioning on melt composition and Nb/Ta fractionation during subduction processes. Earth Planet. Sci. Lett. 226, 415–432. Schmidt A., Weyer S., Mezger K., Scherer E. E., Xiao Y. L., Hoefs J. and Brey G. P. (2008) Rapid eclogitisation of the Dabie-Sulu UHP terrane: constraints from Lu–Hf garnet geochronology. Earth Planet. Sci. Lett. 273, 203–213. Schmidt A., Weyer S., John T. and Brey G. P. (2009) HFSE systematics of rutile-bearing eclogites: new insights into subduction zone processes and implications for the earth’s HFSE budget. Geochim. Cosmochim. Acta 73, 455–468. Schmidt A., Mezger K. and O’Brien P. J. (2011) The time of eclogite formation in the ultrahigh pressure rocks of the Sulu terrane: constraints from Lu–Hf garnet geochronology. Lithos 125, 743–756. Schmitt A. K. and Zack T. (2012) High-sensitivity U–Pb rutile dating by secondary ion mass spectrometry (SIMS) with an O+ 2 primary beam. Chem. Geol. 332–333, 65–73. Schmitz M. D. and Bowring S. A. (2003) Constraints on the thermal evolution of continental lithosphere from U–Pb accessory mineral thermochronometry of lower crustal xenoliths, southern Africa. Contrib. Mineral. Petrol. 144, 592–618. Shannon R. D. (1976) Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Cryst. 32, 751–767. Smith D. C. (1997) Aluminum bearing sphene in eclogites from Sunnmore (Norway). Geology 10, 32–33. Spear F. S., Wark D. A. and Cheney J. T. (2006) Zr-in-rutile thermometry in bluschists from Sifnos, Greece. Contrib. Mineral. Petrol. 152, 375–385. Stacey J. S. and Kramers J. D. (1975) Approximation of terrestrial lead isotope evolution by a two-stage model. Earth Planet. Sci. Lett. 26, 207–221. Stalder R., Foley S. F., Brey G. P. and Horn I. (1998) Mineralaqueous fluid partitioning of trace elements at 900–1200 °C and 3.0–5.7 GPa: new experimental data for garnet, clinopyroxene, and rutile, and implications for mantle metasomatism. Geochim. Cosmochim. Acta 62, 1781–1801. Stepanov A. S. and Hermann J. (2013) Fractionation of Nb and Ta by biotite and phengite: implications for the “missing Nb paradox”. Geology 41, 303–306. Sun S.-S. and McDonough W. F. (1989) Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geol. Soc. Spec. Publ. 42, 313–345.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx Tatsumi Y. and Nakamura N. (1986) Composition of aqueous fluid from serpentine in the subducted lithosphere. Geochem. J. 20, 191–196. Tiepolo M., Vannucci R., Oberti R., Foley S., Bottazzi P. and Zanetti A. (2000) Nb and Ta incorporation and fractionation in titanian pargasite and kaersutite: crystal–chemical constraints and implications for natural systems. Earth Planet. Sci. Lett. 176, 185–201. Tomkins H. S., Powell R. and Ellis D. J. (2007) The pressure dependence of the zirconium-in-rutile thermometer. J. Metamorph. Geol. 25, 703–713. Tropper P. and Manning C. E. (2005) Very low solubility of rutile in H2O at high pressure and temperature, and its implications for Ti mobility in subduction zones. Am. Mineral. 90, 502–505. Vry J. K. and Baker J. A. (2006) LA-MC-ICPMS Pb–Pb dating of rutile from slowly cooled granulites: confirmation of the high closure temperature for Pb diffusion in rutile. Geochim. Cosmochim. Acta 70, 1807–1820. Wade J. and Wood B. J. (2001) The Earth’s “missing” niobium may be in the core. Nature 409, 75–78. Wan Y. S., Li R. W., Wilde S. A., Liu D. Y., Chen Z. Y., Yan L. L., Song T. R. and Yin X. Y. (2005) UHP metamorphism and exhumation of the Dabie Orogen, China: evidence from SHRIMP dating of zircon and monazite from a UHP granitic gneiss cobble from the Hefei Basin. Geochim. Cosmochim. Acta 69, 4333–4348. Wang X. M., Zhang R. Y. and Liou J. G. (1995) UHPM terrane in east central China. In Ultrahigh Pressure Metamorphism (eds. R. Coleman and X. M. Wang). Cambridge University Press, Cambridge, pp. 356–390. Watson E. B., Wark D. A. and Thomas J. B. (2006) Crystallization thermometers for zircon and rutile. Contrib. Mineral. Petrol. 151, 413–433. Whitney D. L. and Evans B. W. (2010) Abbreviations for names of rock-forming minerals. Am. Mineral. 95, 185–187. Wiedenbeck M., Alle P., Corfu F., Griffin W. L., Meier M., Oberli F., von Quadt A., Roddick J. C. and Spiegel W. (1995) Three natural zircon standards for U–Th–Pb, Lu–Hf, trace element and REE analyses. Geostand. Newslett. 19, 1–23. Wilke M., Schmidt C., Dubrail J., Appel K., Borchert M., Kvashnina K. and Manning C. E. (2012) Zircon solubility and zirconium complexation in H2O+Na2O+SiO2±Al2O3 fluids at high pressure and temperature. Earth Planet. Sci. Lett. 349–350, 15–25. Workman R. K. and Hart S. R. (2005) Major and trace element composition of the depleted MORB mantle (DMM). Earth Planet. Sci. Lett. 231, 53–72. Wu Y.-B., Zheng Y.-F., Zhao Z.-F., Gong B., Liu X. M. and Wu F.-Y. (2006) U–Pb, Hf and O isotope evidence for two episodes of fluid-assisted zircon growth in marble-hosted eclogites from the Dabie orogen. Geochim. Cosmochim. Acta 70, 3743–3761. Xia Q.-X., Zheng Y.-F., Yuan H. L. and Wu F.-Y. (2009) Contrasting Lu–Hf and U–Th–Pb isotope systematics between metamorphic growth and recrystallization of zircon from eclogite-facies metagranite in the Dabie orogen, China. Lithos 112, 477–496. Xia Q.-X., Zheng Y.-F. and Hu Z. C. (2010) Trace elements in zircon and coexisting minerals from low-T/UHP metagranite in the Dabie orogen: implications for action of supercritical fluid during continental subduction-zone metamorphism. Lithos 114, 385–412. Xia X. P., Ren Z. Y., Wei G. J., Zhang L., Sun M. and Wang Y. J. (2013) In situ rutile U–Pb dating by laser ablation-MC-ICPMS. Geochem. J. 47, 459–468. Xiao Y. L., Sun W. D., Hoefs J., Simon K., Zhang Z. M., Li S. G. and Hofmann A. W. (2006) Making continental crust through

27

slab melting: constraints from niobium–tantalum fractionation in UHP metamorphic rutile. Geochim. Cosmochim. Acta 70, 4770–4782. Xiong X. L., Adam J. and Green T. H. (2005) Rutile stability and rutile/melt HFSE partitioning during partial melting of hydrous basalt: implications for TTG genesis. Chem. Geol. 218, 339–359. Xiong X. L., Keppler H., Audetat A., Ni H. W., Sun W. D. and Li Y. (2011) Partitioning of Nb and Ta between rutile and felsic melt and the fractionation of Nb/Ta during partial melting of hydrous metabasalt. Geochim. Cosmochim. Acta 75, 1673–1692. Xu Z. Q., Zeng L. S., Liu F. L., Yang J. S., Zhang Z. M., McWilliams M. and Liou J. G. (2006) Polyphase subduction and exhumation of the Sulu high-pressure to ultrahigh-pressure metamorphic terrane. Spec. Pap. Geol. Soc. Am. 403, 93–113. Yang J. J. and Jahn B.-M. (2000) Deep subduction of mantlederived garnet peridotites from the Su-Lu UHPM terrane in China. J. Metamorph. Geol. 18, 167–180. Yao Y. P., Ye K., Liu J. B., Cong B. L. and Wang Q. C. (2000) A transitional eclogite- to high pressure granulite-facies overprint on coesite-eclogite at Taohang in the Sulu ultrahigh-pressure terrane, Eastern China. Lithos 52, 109–120. Ye K., Yao Y. P., Katayama I., Cong B. L., Wang Q. C. and Maruyama S. (2000) Large areal extent of ultrahigh-pressure metamorphism in the Sulu ultrahigh-pressure terrane of East China: new implications from coesite and omphacite inclusions in zircon of granitic gneiss. Lithos 52, 157–164. Zack T., Kronz A., Foley S. F. and Rivers T. (2002) Trace element abundances in rutiles from eclogites and associated garnet mica schists. Chem. Geol. 184, 97–122. Zack T., Moraes R. and Kronz A. (2004) Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer. Contrib. Mineral. Petrol. 148, 471–488. Zack T., Stockli D. F., Luvizotto G. L., Barth M. G., Belousova E., Wolfe M. R. and Hinton R. W. (2011) In-situ U/Pb rutile dating by LA-ICP-MS: 208Pb correction and prospects for thermochronological applications. Contrib. Mineral. Petrol. 162, 515–530. Zhang R. Y., Liou J. G. and Cong B. L. (1994) Petrogenesis of garnet-bearing ultramafic rocks and associated eclogites in the Su-Lu ultrahigh-pressure metamorphic terrane, China. J. Metamorph. Geol. 12, 169–186. Zhang R. Y., Hirajima T., Banno S., Cong B. L. and Liou J. G. (1995) Petrology of ultrahigh-pressure rocks from the southern Su-Lu region, eastern China. J. Metamorph. Geol. 13, 659–675. Zhang Z. M., Xu Z. Q. and Xu H. F. (2000) Petrology of ultrahighpressure eclogites from the southern Dabie mountains, China: the significance of carbonate minerals in UHPM rocks. Am. Mineral. 81, 181–186. Zhang Z. M., Xiao Y. L., Liu F. L., Liou J. G. and Hoefs J. (2005) Petrogenesis of UHP metamorphic rocks from Qinglongshan, southern Sulu, east-central China. Lithos 81, 189–207. Zhang Z. M., Shen K., Sun W. D., Liu Y. S., Liou J. G., Shi C. and Wang J. L. (2008) Fluids in deeply subducted continental crust: petrology, mineral chemistry and fluid inclusion of UHP metamorphic veins from the Sulu orogen, eastern China. Geochim. Cosmochim. Acta 72, 3200–3228. Zhang R. Y., Iizuka Y., Ernst W. G., Liou J. G., Xu Z. Q., Tsujimori T., Lo C.-H. and Jahn B.-M. (2009) Metamorphic P– T conditions and thermal structure of Chinese Continental Scientific Drilling main hole eclogites: Fe–Mg partitioning thermometer vs. Zr-in-rutile thermometer. J. Metamorph. Geol. 27, 757–772. Zhao Z.-F. and Zheng Y.-F. (2009) Remelting of subducted continental lithosphere: petrogenesis of mesozoic magmatic rocks in the Dabie-Sulu orogenic belt. Sci. China D Earth Sci. 52, 1295–1318.

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032

28

X.-Y. Gao et al. / Geochimica et Cosmochimica Acta xxx (2014) xxx–xxx

Zhao Z.-F., Zheng Y.-F., Gao T.-S., Wu Y.-B., Chen B., Chen F. K. and Wu F.-Y. (2006) Isotopic constraints on age and duration of fluid-assisted high-pressure eclogite-facies recrystallization during exhumation of deeply subducted continental crust in the Sulu orogen. J. Metamorph. Geol. 24, 687–702. Zheng Y.-F. (2008) A perspective view on ultrahigh-pressure metamorphism and continental collision in the Dabie-Sulu orogenic belt. Chin. Sci. Bull. 53, 3081–3104. Zheng Y.-F. (2009) Fluid regime in continental subduction zones: petrological insights from ultrahigh-pressure metamorphic rocks. J. Geol. Soc. 166, 763–782. Zheng Y.-F. (2012) Metamorphic chemical geodynamics in continental subduction zones. Chem. Geol. 328, 5–48. Zheng Y.-F., Fu B., Li Y.-L., Xiao Y. L. and Li S. G. (1998) Oxygen and hydrogen isotope geochemistry of ultrahigh pressure eclogites from the Dabie mountains and the Sulu terrane. Earth Planet. Sci. Lett. 155, 113–129. Zheng Y.-F., Fu B., Gong B. and Li L. (2003) Stable isotope geochemistry of ultrahigh pressure metamorphic rocks from the Dabie-Sulu orogen in China: Implications for geodynamics and fluid regime. Earth Sci. Rev. 62, 105–161. Zheng Y.-F., Wu Y.-B., Zhao Z.-F., Zhang S.-B., Xu P. and Wu F.-Y. (2005) Metamorphic effect on zircon Lu–Hf and U–Pb isotope systems in ultrahigh-pressure metagranite and metabasite. Earth Planet. Sci. Lett. 240, 378–400.

Zheng Y. F., Gong B., Zhao Z. F., Wu Y. B. and Chen F. K. (2008) Zircon U–Pb age and O isotope evidence for Neoproterozoic low-18O magmatism during supercontinental rifting in South China: implications for the snowball earth event. Am. J. Sci. 308, 484–516. Zheng Y.-F., Chen R.-X. and Zhao Z.-F. (2009) Chemical geodynamics of continental subduction-zone metamorphism: Insights from studies of the Chinese Continental Scientific Drilling (CCSD) core samples. Tectonophysics 475, 327–358. Zheng Y.-F., Gao X.-Y., Chen R.-X. and Gao T. S. (2011a) Zr-inrutile thermometry of eclogite in the Dabie orogen: Constraints on rutile growth during continental subduction-zone metamorphism. J. Asian Earth Sci. 40, 427–451. Zheng Y.-F., Xia Q.-X., Chen R.-X. and Gao X.-Y. (2011b) Partial melting, fluid supercriticality and element mobility in ultrahighpressure metamorphic rocks during continental collision. Earth Sci. Rev. 107, 342–374. Zheng Y.-F., Zhang L. F., McClelland W. C. and Cuthbert S. (2012) Processes in continental collision zones: preface. Lithos 136–139, 1–9. Associate editor: Weidong Sun

Please cite this article in press as: Gao X. -Y., et al. U–Pb ages and trace elements of metamorphic rutile from ultrahigh-pressure quartzite in the Sulu orogen. Geochim. Cosmochim. Acta (2014), http://dx.doi.org/10.1016/j.gca.2014.04.032