Prolonged anatexis of Paleoproterozoic metasedimentary basement: First evidence from the Yinchuan Basin and new constraints on the evolution of the Khondalite Belt, North China Craton

Prolonged anatexis of Paleoproterozoic metasedimentary basement: First evidence from the Yinchuan Basin and new constraints on the evolution of the Khondalite Belt, North China Craton

Accepted Manuscript Prolonged anatexis of Paleoproterozoic metasedimentary basement: First evidence from the Yinchuan Basin and new constraints on the...
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Accepted Manuscript Prolonged anatexis of Paleoproterozoic metasedimentary basement: First evidence from the Yinchuan Basin and new constraints on the evolution of the Khondalite Belt, North China Craton Wei-(RZ) Wang, Shanlin Gao, Xiaochun Liu, Jianmin Hu, Yue Zhao, Chunjing Wei, Wenjiao Xiao, Hu Guo, Wangbin Gong PII: DOI: Reference:

S0301-9268(17)30362-5 http://dx.doi.org/10.1016/j.precamres.2017.09.007 PRECAM 4879

To appear in:

Precambrian Research

Received Date: Revised Date: Accepted Date:

26 June 2017 9 September 2017 16 September 2017

Please cite this article as: W. Wang, S. Gao, X. Liu, J. Hu, Y. Zhao, C. Wei, W. Xiao, H. Guo, W. Gong, Prolonged anatexis of Paleoproterozoic metasedimentary basement: First evidence from the Yinchuan Basin and new constraints on the evolution of the Khondalite Belt, North China Craton, Precambrian Research (2017), doi: http:// dx.doi.org/10.1016/j.precamres.2017.09.007

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Prolonged anatexis of Paleoproterozoic metasedimentary basement: First evidence from the Yinchuan Basin and new constraints on the evolution of the Khondalite Belt, North China Craton Wei-(RZ) Wanga, d*, Shanlin Gaob*, Xiaochun Liua, Jianmin Hua, Yue Zhao a, Chunjing Weic, Wenjiao Xiaod, Hu Guoe, Wangbin Gonga a

Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China b The Petroleum Exploration and Production Research Institute of SINOPEC, Beijing 100083,China c MOE Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China d State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China e Institute of Geology and Mineral Resources, Tianjin 300170, China * Corresponding author E-mail address: [email protected] / [email protected] Abstract Discerning the history of burial, residence at depth and exhumation of high grade metamorphic rocks from an orogen is essential to understanding crustal differentiation and orogenesis. Such high grade rocks are inferred to exist beneath the Yinchuan Basin, which is overlain by a thick covering of younger sediments, and is located at the inferred southwest boundary of the Paleoproterozoic Khondalite Belt in the northwestern North China Craton. The metamorphic basement sampled from a recently completed deep borehole in the Yinchuan Basin is migmatitic and contains an assemblage of garnet, biotite, sillimanite, plagioclase, quartz, minor K-feldspar and local occurrences of muscovite. Phase equilibrium modelling in the Na2O–CaO–K2O– FeO–MgO–Al2O3–SiO2–H2O–TiO2–O system constrains the peak P–T conditions of anatexis to 6–10 kbar at 760–810°C, followed by final crystallization at 4.5–5.5 kbar and 690–710°C. Ti-in-zircon thermometry for the narrow metamorphic zircon rims provides a temperature range of 687–753°C, demonstrating formation during retrogression to the solidus. NanoSIMS U–Pb analyses on the metamorphic overgrowths of zircon grains yields an upper intercept age of 1895 ± 36 Ma. Chronological and chemical analyses of monazite indicate irregular bright gray domains with relatively high Th and low Y and HREE contents developed during prograde metamorphism (1962 ± 8 Ma). Conversely, dark domains with low Th and high Y and HREE overgrew during retrograde cooling (1892 ± 14 Ma) that was synchronous with the development of metamorphic zircon rims. LA-ICP-MS U–Pb analyses of detrital zircons reveal that the metamorphic basement beneath the Yinchuan Basin has a sedimentary protolith of Paleoproterozoic age. The results directly confirm the existence of Paleoproterozoic basement beneath the Yinchuan Basin, and the well-constrained P–T–t path supports the involvement of the basement (as part of the western Khondalite Belt) in burial and exhumation processes during the 1.96–1.89 Ga period, during which anatexis occurred for ~70 Ma. Keywords: Migmatite; Phase equilibrium modelling; P–T–t path; Zircon

geochronology; Ti-in-zircon thermometry; Prograde/retrograde monazite. 1. Introduction The North China Craton (NCC) consists of an Archean and Paleoproterozoic metamorphic basement overlain by Mesoproterozoic or younger unmetamorphosed sedimentary cover (Trap et al., 2012). Understanding its formation and evolution provides insights into geological processes in the early Earth. Extensive field-based structural, metamorphic, geochemical, geochronological and geophysical investigations of the basement have been carried out to interpret the Precambrian history of the NCC (Zhao et al., 1999, 2001, 2005; Zhai et al., 2000; Guo et al., 2002; Wilde et al., 2002; Trap et al., 2007, 2012; Chen et al., 2009; Trap et al., 2012; Zhao and Zhai, 2013;Wei et al., 2014; Wang et al., 2014a; Cai et al., 2017). However, critical issues related to the metamorphic history, such as the amalgamation of the NCC, remain in dispute, which has led to different tectonic models being proposed (e.g. Zhao et al., 2005; Zhai et al., 2000, 2005; Trap et al., 2007, 2012; Zhao and Zhai, 2013; Kusky et al., 2003, 2011; Wei et al., 2014). The differences between tectonic models necessitate further detailed investigation of the metamorphic process of high grade rocks that could be correlated with tectonic evolution. The NCC is generally considered to have formed by the amalgamation of the Eastern and Western Blocks, with the latter subdivided into the Yinshan and Ordos Blocks (Fig. 1a; Zhao et al., 2005). Between the Yinshan and Ordos Blocks is the E– W trending Khondalite Belt, a Paleoproterozoic orogenic belt extending from the Helanshan and Qianlishan Complexes in the west, through the Daqingshan and Wulashan Complexes and into the Jining Complex in the east (Lu et al., 1992, 1996; Fig. 1b).The extent of the Khondalite Belt is inferred based on limited exposures of Paleoproterozoic lithologies, while the Yinchuan Basin, which is covered with thick Cenozoic sediments, is located near the inferred boundary between the Khondalite Belt and the Ordos Block in the Western Block (Ningxia Geological Bureau, 1980; Hao et al., 2011; Zhang et al., 2014). The nature of the basement beneath the Yinchuan Basin remains unclear as there is virtually no exposure. A recently completed deep borehole in the Yinchuan Basin makes direct investigation of the metamorphic basement possible. The basement migmatite samples originate from partial melting and records critical information about the composition, melting processes and the pressure-temperature-time (P–T–t) history of the basement at middle to lower crust depths. Although there have been many detailed studies on the P–T conditions and metamorphic ages of granulites from the Khondalite series rocks (e.g. Yin et al., 2009, 2014; Jiao et al., 2013a; Cai et al., 2017), few efforts have been made to precisely link metamorphic ages with specific P–T conditions to retrieve a more complete history of the prograde and retrograde processes that reflect the burial and exhumation of the ancient orogen. Phase equilibrium modelling with an improved dataset and activity-composition models allows for construction of P–T paths for high grade rocks that have undergone anatexis (Holland and Powell, 2011; White et al., 2014) and dating of accessory minerals such as zircon and monazite provides temporal constraints on the metamorphic P–T paths, especially if their chemical features are also carefully analyzed (Rubatto 2002; Harley et al. 2007; Williams et al. 2007; Kelsey et al. 2008; Reno et al. 2012; Korhonen et al. 2013; Yakymchuk & Brown, 2014). In this paper we present an investigation into the basement migmatite beneath the Yinchuan Basin which involves integration of detailed petrography, phase equilibrium modelling, geochronology and chemical analyses of zircon and monazite.

The results reveal the geological characteristics of the basement, particularly the links between the ages of metamorphic zircon and monazite with the P–T stages. This relationship enables the construction of a complete P–T–t trajectory, providing robust constraints on the timing and duration of anatexis in the basement of the Yinchuan Basin and hence the evolution of the Khondalite Belt in the NCC. 2. Geological setting and sampling The NCC extends across North China and most of the Korean Peninsula for ~1.5 million km2 and is bounded by the Central Asian Orogenic Belt in the north, the SuLu Orogen in the east, the Qinling-Dabie Orogen in the south and the Qilianshan Orogen in the west (Fig. 1a; Zhao et al., 1999, 2005; Zhai et al., 2000; Zheng et al., 2013). Based on existing data, a few models have been proposed to illustrate the evolution of the craton (Zhao et al., 1998, 2005; Zhai et al., 2000; Kusky and Li, 2003; Trap et al., 2007, 2012; Zhao and Zhai, 2013; Wei et al., 2014). One of the major models shows that the NCC was cratonized by the amalgamation of micro-blocks and island arcs at ~2.5 Ga and was subsequently imprinted by a series of Paleoproterozoic tectonic events involving rifting, subduction, accretion and collision during the transition from extension (2.3–2.0 Ga) to compression (2.01–1.97 Ga) (Zhai et al., 2000, 2005; Zhai and Liu, 2003; Zhai and Santosh, 2011). The models of Zhao et al. (1998, 1999, 2005) involve an Archean to Paleoproterozoic cratonic basement subdivided into four blocks (Yinshan, Ordos, Longgang and Langrim Blocks) and three mobile belts (Khondalite Belt, Jiao-Liao-Ji Belt and Trans-North China Orogen) (Zhao et al., 2005; Zhao and Cawood, 2012). The Yinshan and Ordos Blocks in the west are considered to have amalgamated along the E–W trending Khondalite Belt to form the Western Block (Xia et al., 2008; Zhao, 2009, Zhou et al., 2010; Li et al., 2011, Wang et al., 2011) and the Longgang and Langrim Blocks were fused along the Jiao-Liao-Ji Belt to form the Eastern Block at ~1.90 Ga (Li et al., 2006, 2011, 2012; Li and Zhao, 2007; Zhou et al., 2008; Tam et al., 2011). Finally, the Western Block was fused along the N–S trending Trans-North China Orogen with the Eastern Block at ~1.85 Ga to form the basement of the NCC (Zhao et al., 2005; Zhang et al., 2006; Li et al., 2010; Xiao et al., 2011) (Fig. 1). The models of Trap et al. (2007, 2008, 2012) involve three Archean continental blocks (Western, Fuping and Eastern blocks) that were separated by the Lüliang and Taihang Oceans before becoming welded together during the Paleoproterozoic Lüliangian Orogeny. The model of Kusky and Li (2003, 2011) includes microcontinental /arc collisions forming the Eastern and Western Blocks between 3.5 and 2.7 Ga, rifting of the western edge of the Eastern Block at 2.7 Ga, collision of an arc on the eastern edge of the Western Block at 2.5 Ga, and then a major continent-continent collision along the entire north margin of the craton at circa 1.85 Ga. The Yinchuan Basin is situated near the inferred boundary between the Khondalite Belt and Ordos Block while, to the north, the E–W trending Khondalite Belt extends for up to ~1000 km, and consists mainly of high-grade graphite-bearing garnetsillimanite pelitic gneiss, garnet quartzite, felsic paragneiss, calc-silicate gneiss and marble. Collectively, these lithologies are referred to as ‘khondalite’ or ‘Khondalite Series’ (Qianet al., 1985; Shen et al., 1992). Minor tonalite-trondhjemite-granodiorite (TTG) gneiss, mafic granulite, syntectonic charnockite, and S-type granite are associated with the Khondalite Series (Zhao and Zhai, 2013). Ultrahigh temperature (UHT) granulites are known from the northeast of the Khondalite Belt (Jin, 1989; Liu et al., 1993, 2000; Santosh et al., 2007, 2009; Guo et al., 2012; Yang et al., 2014). Recent studies show that the Khondalite Belt underwent long-term arc-continent

accretion before the Paleoproterozoic collision between the Yinshan and Ordos Blocks (e.g. Liu et al., 2017). To the south, the Ordos Block is completely covered by thick Mesozoic to Cenozoic sediments of the Ordos Basin. Basement rocks collected from drill cores have been recently investigated, with Paleoproterozoic granulite facies metamorphism being confirmed in the northern margin of the Ordos Basin (Wan et al., 2013a; Wang et al., 2014a; Gou et al., 2016). The recently completed deep borehole YC4 is located in the northeast of the Yinchuan Basin, and for the first time penetrated the metamorphic basement beneath the basin cover of Cenozoic sedimentary lithologies and unconsolidated Quaternary sediments (Hao et al., 2011; Zhang et al., 2014, Fig. 1c). The borehole has a total depth of 4124 m, but extends only ~ 2 m into the basement (Zhang et al., 2014). Stratigraphically, the sedimentary cover includes the Oligocene Qingshuiying Formation, the Miocene Hongliugou Formation and the Pliocene Ganhegou Formation. The basement sample (YC4-1) was collected from a depth of ~4124 m (Fig. 1d). 3. Analytical methods Mineral compositions were analyzed using a JEOL JXA-8100 wavelengthdispersive electron microprobe at the MOE Key Laboratory of Orogenic Belts and Crustal Evolution at Peking University. The operating conditions were as follows: accelerating voltage of 15 kV, 10 nA beam current and counting time of 10 s for each peak. The beam diameter was set to 1 µm for all minerals and natural minerals were used as standards. Zircon and monazite grains were separated using standard heavy liquid and magnetic techniques, and after separation were hand-picked and mounted in epoxy resin discs. Mounts were polished until all grains were transected. To assist in the isotope analysis, zircon grains were photographed in transmitted and reflected light and then imaged using cathodoluminescence (CL) to ensure that analyses would not mix detrital and metamorphic domains. CL imaging was completed on a FEI PHILIPS XL30 SFEG Scanning Electron Microscope (SEM), with a 2 min scanning time and operating conditions of 15 kV and 120 µA. Backscattered electron (BSE) images were obtained for monazite using the same electron microprobe. The U–Pb and Ti contents of the narrow metamorphic zircon overgrowths were analyzed using a CAMECA NanoSIMS 50L at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). The advantage of the coaxial design of the NanoSIMS is the reduction in objective-sample distance (0.4 mm) that provides very low aberration coefficients and thus a smaller spot size for a given probe current than conventional SIMS (Hillion et al., 2000, Yang et al., 2012). The O– primary beam was optimized to a current of ~500 pA with a diameter of 1.7 µm. The U–Pb analyses of zircon overgrowths were executed in scanning mode by rasterizing 3 × 3 µm2 areas to eliminate pit depth-dependent U−Pb fractionation (Yang et al., 2012). The Plešovice and 91500 zircons were used as standards in the U−Pb analyses. The Ti contents of zircon overgrowths were analyzed according to the procedures described in Yang et al. (2016). U–Pb dating of the detrital zircon was conducted using LA-ICP-MS at the Sample Solution Company laboratory, Wuhan. Detailed operating conditions used in the laser ablation system, ICP-MS instrument and data reduction are described by Liu et al. (2008; 2010). Laser sampling was performed with a GeoLas 2005 and an Agilent 7700e ICP-MS instrument was used to acquire ion-signal intensities. Helium was used as the carrier gas, with argon added as the make-up gas which was mixed with

the helium via a T-connector before entering the ICP. A ‘wire’ signal smoothing device was included in the laser ablation system, allowing for smooth signals even at very low laser repetition rates (down to 1 Hz) (Hu et al., 2012). Each analysis incorporated a background acquisition rate of approximately 20–30 s (gas blank) followed by 50 s of data acquisition from the sample. Zircon 91500 was used as external standard for U–Pb dating, and was analyzed twice every five analyses. Timedependent drift in the U–Th–Pb isotopic ratios was corrected using linear interpolation (with time) for every five analyses, based on variations in zircon 91500 (i.e., 2 × zircon 91500 + 5 samples + 2 × zircon 91500) (Liu et al., 2010). The preferred U–Th–Pb isotopic ratios used for zircon 91500 were obtained from Wiedenbeck et al. (1995). U–Pb dating and trace element analyses of monazite were conducted using LAICP-MS in the same laboratory. Laser sampling was performed with a GeolasPro laser ablation system, consisting of a COMPexPro 102 ArF excimer laser (wavelength of 193 nm and maximum energy of 200 mJ) and a MicroLas optical system. An Agilent 7700e ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas with argon added via a T-connector as a make-up gas. The spot size and frequency of the laser were set to 10 µm and 3 Hz, respectively, for dating the bright gray domains of monazite and 16 µm and 2 Hz, respectively, for dating the dark domains and analyzing trace elements. Monazite standard 44069 and glasses NIST610, BHVO-2G, BCR-2G and BIR-1G were used as external standards for U–Pb dating and trace element calibration, respectively. Each analysis incorporated a background acquisition of approximately 20–30 s followed by 50 s of data acquisition. For both zircon and monazite analyses, an in-house spreadsheetbased software was used to perform off-line selection, integration of background and analyte signals, time-drift correction and quantitative calibration of trace element analysis and U–Pb dating (ICPMSDataCal, ver. 10.0) (Liu et al., 2008; Liu et al., 2010). Concordia diagrams and weighted mean calculations were made using Isoplot 3 software (Ludwig, 2003). 4. Petrography and mineral composition Basement sample YC4-1 has the appearance of migmatite, with domains rich in dark or felsic minerals (Fig. 2a).The mineral assemblage includes garnet (~5–10%), biotite (~5–10%), sillimanite (~5 %), plagioclase (~35%), quartz (~35 %), minor Kfeldspar (~5 %), local muscovite and accessory ilmenite, barite, zircon and monazite (Fig. 2b–m). Garnet grains vary in size from ~0.5 mm to a few millimeters and usually contain inclusions of round quartz and biotite (Fig. 2b–d). The biotite flakes (~0.2–1 mm) are usually short, brown in color and lack a strong foliation (Fig. 2b, c, e, f, j, k). Biotite and sillimanite frequently occur around the garnet grains (Fig. 2e), while perthite or K-feldspar occasionally appear as relicts (Fig. 2g–j). The rare muscovite is developed only in K-feldspar- and sillimanite-rich domains. The mineral textures show a retrograde origin for muscovite, probably from the reaction ksp+sill+liq → mus+q (Fig. 2h–j). Some plagioclase grains in the felsic domains are perfectly euhedral with straight crystal edges, implying unimpeded growth (Fig. 2l). Interstitial quartz with low dihedral angles also demonstrates the former presence of silicate melt (Fig. 2k, m; Holness et al., 2008; 2011). Based on mineral textures, the peak assemblage is inferred to include garnet, biotite, sillimanite, plagioclase, Kfeldspar, ilmenite and quartz. The major retrograde assemblage comprises garnet, biotite, sillimanite, plagioclase, ilmenite and quartz and the local retrograde assemblage includes biotite, sillimanite, muscovite, K-feldspar, plagioclase. Garnet compositions and the mole fractions of end-members are listed in Table 1.

All garnet compositions are almandine-rich (XAlm = 0.795–0.864; X(g) = Fe2+/ (Fe2+ + Mg) = 0.826–0.914) with minor pyrope (XPy = 0.081–0.168) and very low concentrations of spessartine (XSps = 0.013–0.036) and grossular (XGrs = 0.020–0.025) (Table 1; Fig. 3a–i). Zoning profiles of representative garnet grains show weak compositional variation from rim to core, with increasing pyrope and decreasing almandine close to the relict cores (Fig. 3). The larger garnet grain (Grain 3 in Table 1; Fig. 3g, h, i) preserves higher pyrope (XPy = 0.112–0.168) and lower almandine (XAlm= 0.795–0.851) and spessartine (XSps = 0.013–0.019) compositions than other grains. The variation in garnet composition can be attributed to retrograde reequilibration and/or subsolidus retrograde Fe–Mg exchange. Biotite exhibits minor compositional variation between different grains, with XFe = Fe2+/ (Fe2+ + Mg) = 0.615–0.654, and Ti = 0.108–0.155 cations per formula unit (c.p.f.u). Plagioclase displays some minor variation in composition with An in the 16.71–21.53% range (Table 2). 5. Mineral equilibria modelling and P–T path The model system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O (NCKFMASHTO) was used to construct P–T diagrams for sample YC4-1 using THERMOCALC (ver. 3.40, Powell and Holland, 1988, updated 2013) with the internally consistent thermodynamic dataset (DS62) of Holland and Powell (2011). Minerals and activity models used in the construction of the P–T pseudosections are the same as those in White et al. (2014). Aluminosilicates (and/sill/ky), quartz (q) and water (H2O) were modelled as pure end-member phases. Based on X-ray fluorescence analyses, the reintegrated bulk composition for sample YC4-1 in mole percent is: SiO2: 76.91; Al2O3: 9.58; CaO: 2.27; MgO: 1.78; FeO: 3.84; K2O: 1.04; Na2O: 4.06; TiO2: 0.30; O: 0.19 and H2O: 3. An assumption of ferric-ferrous iron proportions was made, involving 10% ferric iron, based on mineral chemistry and test modelling to obtain oxide proportions that matched those present in thin section. Water was considered to be in excess for the modelling in sub-solidus conditions. A fixed proportion of 3 mol %, just sufficient to saturate equilibria immediately below the solidus, was applied for supra-solidus conditions. The equilibria modelled for the range of conditions T = 650–900°C and P = 1–12 kbar for sample YC4-1 is shown in Fig. 4a. Most equilibria are quadri-, quini- or hexavariant with a few trivariant equilibria and a divariant equilibrium. Garnetbearing equilibria occur in most of the P–T range, except in the very low pressure region. At relatively high pressure, K-feldspar appears at temperatures higher than ~760°C. Muscovite is present in the low-T and high-P region, while aluminosilicates are present in most equilibria. Cordierite occurs in the low-P equilibria. The solidus temperature between 3–10 kbar is in the 670–695°C range. The modes of garnet, biotite, sillimanite, liquid and compositional isopleths involving X(g) = Fe2+/(Fe2++ Mg), Z(g)= Ca/(Fe2++ Mg + Ca) and X(bi)= Fe2+/(Fe2++ Mg) were contoured for related fields (Fig. 4a, c–h). The observed peak assemblage corresponds to a quadrivariant field of garnet, biotite, sillimanite, plagioclase, K-feldspar, ilmenite, quartz and liquid at P–T conditions of 6–10 kbar and 760–810°C (stage A in Fig. 4g). This may reflect the minimum peak conditions during which extensive anatexis could be expected to have occurred (Fig. 4h). The texture and composition of biotite in the sample imply a retrograde origin, and if all biotite was formed during retrogression, the basement rock could have entered fields without biotite at temperatures exceeding 810°C (Fig. 4a, d). The formation of sillimanite around garnet also suggests a retrograde process (Fig. 4e). The garnet grains could have developed at or around the

peak metamorphism, as shown by the variation in mode isopleths (Fig. 4c), but then re-equilibrated, thereby recording the retrograde stage with X(g) exceeding those for the model garnet composition in the peak field (Fig. 4g; Table 1). The anorthite (An) zoning in plagioclase-rich granulites tends to reflect high temperature conditions of granulite thermal history (Li and Wei, 2016). However, the An components of plagioclase in the basement migmatite are relatively low (Table 2), reflecting lower temperature conditions. This may have occurred as the migmatite underwent significant retrogression in fluid-rich (mainly water) conditions, as shown by the strong development of biotite around garnet (Fig. 2b, c, e, k). Most of the plagioclase may have crystallized from silicate melt around the wet solidus and the limited peak plagioclase may have changed in composition during the coolingcrystallization process. The absence of cordierite in the sample suggests that the basement rock developed above the cordierite stable fields (Fig. 4a), and together with the relict garnet core compositions (e.g. grain 3 in Fig. 3, X(g) > 0.836, Z(g) < 0.03) and biotite compositions (X(bi) > 0.6) (Fig. 4f-g), constrains a narrow corridor around the H2O saturated solidus, with above-solidus conditions of 4.5–5.5 kbar and 690–710°C (stage B in Fig. 4g). Further cooling would be largely isobaric from stage B to subsolidus stage C. Given that muscovite only developed in K-feldspar- and sillimanite-rich domains, its formation must have been controlled by a local potassium- and aluminum-rich composition. Based on the local mineral assemblage including the very high Kfeldspar and sillimanite components, the local composition (YC4-1L) was estimated to contain the following oxide proportions (in mole percent): SiO2: 70.12; Al2O3: 19.38 ; CaO: 0.18; MgO: 1.08; FeO: 3.22; K2O: 4.35; Na2O: 0.73; TiO2: 0.93; O: 0.01 and H2O: 4. The equilibria modelled for the local composition in the range of T = 650–900°C and P = 1–12 kbar is shown in Fig. 4b. Most equilibria are quini- or hexavariant with a few quadri- and two tri-variant equilibria. Muscovite occurs in the low temperature and high pressure fields. Muscovite begins to form at temperatures of 680–700°C in the 4.5–5.5 kbar pressure range, which is consistent with the temperature for retrograde stage B (Fig. 4g). The locally present muscovite in domains rich in K-feldspar and sillimanite is likely to have formed near the solidus during retrograde crystallization along the inferred P–T path. 6. Geochronological and chemical analyses 6.1. NanoSIMS U–Pb age and Ti contents of metamorphic zircon overgrowth The zircon grains separated from sample YC4-1 vary in size, with the majority in the 40–150 µm range (Fig. 5). Most of the grains are transparent and prismatic and the CL images show that many cores of the detrital zircons have clear oscillatory zoning, suggesting an igneous origin (Corfu et al., 2003). Some grains have intermediate luminescence and are almost homogeneous with blurred zoning or no zoning. The distinct morphologies among the zircon grains imply distinct sources. Metamorphic overgrowths, usually narrower than 10 µm, have developed around some of the detrital zircon (Fig. 5).The results of NanoSIMS U−Pb analyses on the narrow overgrowths are presented in Table 3. Although many data points are discordant, probably because of loss of Pb, together with concordant /nearly concordant data points, they define an upper intercept age of 1895 ± 36 Ma (MSWD = 0.66, n=13) (Fig. 6a). The weighted mean 207Pb/206Pb age (1840 ± 17 Ma, MSWD = 1.9, n = 13) for the discordant and nearly concordant data points is lower than the upper intercept age. Ti contents of the metamorphic zircon overgrowths were

analyzed using the NanoSIMS method. Seven analyses obtained Ti contents in the 5.1–10.8 ppm range, among which five are in the 5.1–6.4 ppm range and two higher Ti values of 10.0 ppm and 10.8 ppm. 6.2. LA-ICP-MS U–Pb age of detrital zircon The LA-ICP-MS U–Pb analyses of 62 detrital zircon grains indicate that the Th/U ratios for the detrital cores are relatively high, predominantly in the 0.2–1.0 range, with a minimum value of 0.12 and maximum value of 1.39 (Table 4). Most analyses are concordant or nearly concordant (> 95 %) with 207Pb/206Pb ages in the 2432–2005 Ma range (Table 4, Fig. 6b, c). Six analyses that are discordant (≤ 95 %) are not considered in Fig. 6c. Although the youngest single-grain ages are generally compatible with depositional ages, it is more statistically robust to take the mean of multiple young ages that overlap within analytical uncertainty (Dickinson and Gehrels, 2009). The nine youngest concordant 207Pb/206Pb ages that overlap within analytical uncertainty yield a weighted mean of 2019 ± 22 Ma. The age data support that the sedimentary protoliths of the basement were sourced from Paleoproterozoic rocks and were deposited no earlier than ~2019 Ma. 6.3. LA-ICP-MS U–Pb ages and chemical analyses of monazite Monazite grains separated from the basement sample are subhedral to rounded and vary in size, with the majority in the 3–160 µm range. Monazite grains typically display bright gray and irregular relict patches or cores and homogeneous dark overgrown domains in BSE images (Fig. 7). Inclusions of quartz and plagioclase were found in the dark domains. The bright gray domains were analyzed and13 analyses are concordant, providing a concordia age of 1962 ± 8 Ma (MSWD = 0. 24, Fig. 8a; Table 5). Analyses of the homogenous dark domains yield an upper intercept age of 1892 ± 14 Ma (MSWD = 0.88, n=30, Fig. 8b; Table 5). The weighted mean 207 Pb/206Pb age (1914 ± 12 Ma, MSWD = 0.75, n = 30) of the analyses is slightly higher than the upper intercept age. The bright gray domains of the monazite have relatively high Th contents (58474–81849 ppm), low Y (3028–3048 ppm) and heavy rare earth elements (HREE).The dark domains of the monazite have relatively low Th (32978–65678 ppm) and high Y (6970–24669 ppm) and HREE (Table 6; Fig. 8c, d). The light rare earth elements (LREE) of the two types of monazite domains are comparable, without obvious difference. 7.Ti-in-zircon thermometry The formula of Ferry and Watson (2007), shown below in Eq. (1) was used for estimating the Ti-in-zircon temperature. log(ppm Ti-in-zircon) = (5.711 ± 0.072) – (4800 ± 86/T(K)) −logαSiO2+ logαTiO2

(1)

As quartz is abundant in the sample, the value of SiO2 activity (αSiO2) was considered to be 1. The common occurrence of accessory ilmenite suggests saturation of Ti and therefore the activity of TiO2 (αTiO2) was also assumed to be 1. Seven analyses of the metamorphic rims gave Ti contents in the 5.1–10.8 ppm range, yielding a temperature range of 687–753°C. Five of the seven analyses cluster between 5.1 ppm and 6.4 ppm, corresponding to a temperature range of 687–705°C, which is consistent with the retrograde crystallization temperature range of 690– 710°C at 4.5–5.5 kbar estimated from phase equilibrium modelling and mineral compositions. Two analyses with high Ti contents of 10.0 ppm and 10.8 ppm gave

temperatures of 746°C and 753°C, respectively. The Ti-in-zircon temperatures support that the metamorphic rims were formed during retrogression when partial melt was crystallizing. 8. Discussion 8.1. Protolith of the basement beneath the Yinchuan Basin The metamorphic basement of the Yinchuan Basin is overlain by Cenozoic sedimentary lithologies and Quaternary unconsolidated sediments (Ningxia Geological Bureau, 1980; Hao et al., 2011; Zhang et al., 2014) with no basement rock exposure. To the north of the basin are exposures of the Khondalite Belt, including the Helanshan and Qianlishan Complexes (Lu et al., 1996). To date, there has been no direct geochronological evidence of the metamorphic basement beneath the Yinchuan Basin. The work presented in this study shows that detrital zircons of the basement have concordant or nearly concordant 207Pb/206Pb ages predominantly in the 2432– 2005 Ma range, with a peak at 2100 Ma (Fig. 6c, Table 4). These ages and other accumulated geological data show that the sedimentary protolith of the Khondalite Belt, including the Jining, Daqingshan, Helanshan and Qianlishan Complexes, are predominantly Paleoproterozoic in age (> 2000 Ma) with only a few Neoarchean ages (Wan et al., 2006; Yin et al., 2009, 2011; Wan et al., 2009; Donget al., 2013; Wang et al., 2014a; Cai et al., 2017). Additionally, the age data show that the protoliths must have been deposited in the Paleoproterozoic rather than Neoarchean (Lu et al., 1992, 1996; Li et al., 1999; Qian and Li, 1999) or Mesoarchean (Yang et al., 2000). However, from the Jining Complex in the east to the Qianlishan-Helanshan Complex in the west, the age peaks for the protoliths of the Khondalite Belt vary, with a major peak at 2020 Ma for the metapelitic rocks of the Qianlishan-Helanshan Complex to the north of the Yinchuan Basin (Zhou and Geng, 2009; Qiao et al., 2016; Cai et al., 2017). To the east of the Yinchuan Basin, the basement of the northern margin of the Ordos Basin has a protolith with a major Paleoproterozoic age population, except for a few Archean ages (Wan et al., 2013a; Wang et al. 2014a). The age data from the basement sample of the Yinchuan Basin are comparable with those of basement rocks in the adjoining regions and demonstrate that the sedimentary protoliths of the Yinchuan Basin basement were mainly derived from Paleoproterozoic material and were deposited during the early Orosirian Period in the Paleoproterozoic (< 2019 Ma). 8.2. Metamorphism of the basement migmatite beneath the Yinchuan Basin Detailed petrological examination and thermodynamic modelling confirm that the basement rocks beneath the Yinchuan Basin have undergone anatexis at medium pressure granulite facies conditions. The peak P–T conditions were constrained to 760–810ºC at 6–10 kbar for the assemblage including garnet, sillimanite, biotite, Kfeldspar, plagioclase and quartz. Retrograde crystallization followed at 690–710°C at 4.5–5.5 kbar with further subsolidus cooling, thus most likely establishing a clockwise P–T path as is the case for many granulites in the Khondalite Belt. Medium pressure granulites that have been subjected to partial melting are common in the Khondalite Belt, with local occurrences of high pressure granulites in the Helanshan, Qianlishan and Jining Complexes (Zhou et al., 2010; Wang et al., 2011; Yin et al., 2014) and UHT granulites in the Daqingshan Complex (Jin, 1989; Liu et al., 1993, 2000; Guo et al., 2006; Wan et al., 2009; Guo et al., 2012) and Jining Complex (Santosh et al., 2006, 2007; Liu et al., 2010; Yang et al., 2014; Li and Wei, 2016). Medium and high pressure pelitic granulites commonly have clockwise P–T paths in contrast to the proposed counterclockwise P–T paths for some UHT granulites (Fig.

9 and related references). The recently recognized UHT granulite at Hongsigou within the eastern segment of the Khondalite Belt has a clockwise P–T path with evidence of isobaric heating (Yang et al., 2014). Some pelitic granulites without diagnostic UHT indicators may also have undergone UHT metamorphism and evolved along clockwise P–T paths (Li and Wei, 2016). Most P–T paths for the medium and high pressure granulites have a decompression stage and retrograde cooling stage that proceed to lower temperature conditions around the effective solidus (Fig. 9). As illustrated by the P–T paths compiled (especially for high pressure pelitic granulites from the Khondalite Belt) a remarkable degree of cooling commenced at pressures in the 5–8 kbar range. This occurred after various pressure drops, suggesting that these granulites were quickly exhumed to shallow crustal depths with different geothermal gradients before retrograde cooling, or they experienced a possible tectonic regime change (Yamato and Brun, 2017). The differences in crustal levels and geothermal environment influence the rate and processes of cooling, as well as the development of accessory minerals of geochronological importance. The metasedimentary basement beneath the Yinchuan Basin underwent prograde metamorphism to medium pressure granulite facies followed by retrograde cooling and decompression along a clockwise P–T path, reflecting an integral orogenic cycle of burial and exhumation. 8.3. Timing and duration of anatexis and constraints on the evolution of the Khondalite Belt Understanding orogenic processes requires reconstruction of the metamorphic history of high grade rocks in terms of their P–T evolution and timing, and linking the two together. Both zircon and monazite from the basement sample provided ages and chemical compositions with which to establish a link between the metamorphic ages and metamorphic conditions/stages. The NanoSIMS U–Pb analyses yielded a late Paleoproterozoic metamorphic age of 1895 ± 36 Ma for the narrow zircon overgrowths while Ti-in-zircon thermometry revealed that the metamorphic zircon overgrowths developed in the 687–753°C temperature range. This corresponds with cooling and crystallization of the partially melted basement, thus the metamorphic age correlates with the retrograde rather than the peak stage. This is consistent with the behavior of metamorphic zircon in granulites subjected to partial melting, where the growth of zircon mainly occurs during melt crystallization (Kelsey and Powell, 2011; Wang et al., 2014b). The LA-ICP-MS age of 1892 ± 14 Ma for the dark domains of monazite is comparable with the age of metamorphic zircon overgrowth. However, the bright gray domains of monazite provided an age of 1962 ± 8 Ma that was not recorded in zircon. Compared with zircon, monazite is usually less resistant to alteration and may recrystallize with the aid of fluids or deformation, allowing even a single monazite grain to record several tectonothermal stages (Högdahl et al., 2012; Didier et al., 2014; Taylor et al., 2014; Kirkland et al., 2016). In high grade conditions, monazite may gradually dissolve into an anatectic melt (Rapp et al., 1987; Kelsey et al., 2008), although prograde monazite may partially survive anatexis if the melt/monazite ratio at the local scale is appropriate (Rubatto et al., 2013; Yakymchuk and Brown, 2014). The similarities in ages indicate that the dark monazite domains (1892 ± 14 Ma) formed synchronously with zircon overgrowths during retrograde cooling. This is also supported by the chemical features of the monazite. The dark domains of the monazite have relatively low Th and high Y and HREE. The relative depletion in Th could be related to strong partitioning into the melt, although the influence of crystallization of other minerals on the abundance of Th in monazite cannot be excluded (Spear 2010;

Konh, 2016). The variation in Y and HREE can be linked to the growth or breakdown of garnet (Konh, 2016). Along the retrograde segment of the P–T path, the mode of garnet decreases (Fig. 4c), releasing HREE and Y elements, resulting in the high Y and HREE contents of the newly grown dark monazite. By contrast, the bright gray domains of monazite have relatively high Th and low Y and HREE, consistent with their formation in a late prograde assemblage before muscovite dehydration-melting (low Y and relatively high Th, ≤ ~700°C) (Konh, 2016). Depletion in Y and HREE suggests garnet formation accompanied the development of the bright gray monazite. The relatively strong Eu anomalies in the bright gray monazite domains may be attributed to the increase in K-feldspar during prograde metamorphism. Monazite is soluble in partial melts and peak metamorphic monazite in anatectic rocks is generally not expected (Rapp et al. 1987; Montel 1993; Konh, 2016). The textures of the bright gray monazite domains also suggest they are basically relicts of early monazite after dissolution during partial melting. Therefore, the bright gray monazite domains must have developed during the prograde stage before voluminous melt occurred. The age data for the detrital zircons (> 2000 Ma) help to exclude the possibility that the bright gray monazite domains were inherited. The metamorphic ages of zircon and monazite bracket the duration of the prolonged anatexis to ~70 Ma in the basement beneath the Yinchuan Basin in the western Khondalite Belt. Monazite and zircon lost their U–Pb “memory” for~70 Ma during anatexis, a phenomenon consistent with experimental and theoretical results that show Zr and LREE tend to be absorbed by increasing melt fractions during anatexis (Watson and Harrison, 1983; Rapp et al., 1987; Kelsey et al., 2008; Yakymchuk and Brown, 2014). The links between the metamorphic ages of zircon and monazite and the P–T stages enable the establishment of a more complete P–T–t trajectory for the basement (Fig. 9). There is a relatively large dataset of late Paleoproterozoic metamorphic and magmatic zircon ages for the Khondalite Belt, which helps to constrain the timing of metamorphism. Meta-mafic rocks in the Jining Complex east of the Khondalite Belt have magmatic ages of 1.96–1.95 Ga and metamorphic ages of 1.92–1.86 Ga (Peng et al., 2010), in contrast to the magmatic ages of 1.97–1.92 Ga and metamorphic ages of 1.95–1.83 Ga in the Daqingshan Complex (Wan et al., 2013b). The metamorphic age for supra-crustal rocks is in the 1.96–1.83 Ga range for the Daqingshan Complex (Wan et al., 2009; Donget al., 2013; Wan et al., 2013b), in the 1.91–1.87 Ga range for the Jining Complex (Li et al., 2011; Santosh et al., 2013; Jiao et al., 2013a; Cai et al., 2017), and in the 1.95–1.87 Ga range for the Qianlishan-Helanshan Complex (Zhou and Geng, 2009; Yin et al., 2009; 2011; Qiao et al., 2016). The UHT granulites in the Khondalite Belt have metamorphic ages of 1.92 Ga (Santosh et al., 2006, 2007) and 1.88 Ga (Yang et al., 2014). S-type granites related to partial melting of supracrustal rocks in the Khondalite Belt were emplaced at 1.93–1.86 Ga (Guo et al., 2001; Zhong et al., 2007; Yin et al., 2011; Guo et al., 2012). The metamorphic ages of 1.96 Ga and 1.89 Ga determined in this study for the basement of the Yinchuan Basin are largely within the same time span revealed by rocks exposed in the Khondalite Belt. However, the younger metamorphic age populations for the western Khondalite Belt seem to be slightly older than those of the eastern Khondalite Belt, possibly reflecting differences in tectonothermal evolution after collision and early stages of exhumation. The Khondalite Belt can be considered an orogenic belt situated between the Yinshan and Ordos Blocks, with a metamorphic age of 1.96–1.95 Ga for the metamorphosed supra-crustal and magmatic rocks in the Khondalite Belt being interpreted as the time of collision between the Yinshan and Ordos Blocks (Zhao et al., 2005; Yin et al., 2011; Wang et al., 2014a). UHT granulites developed later, between

1.92 Ga and 1.88 Ga (Santosh et al., 2006; 2007; Yang et al., 2014). Different models for this heating have involved post-collisional extension mantle upwelling (Zhao et al., 2009), asthenospheric upwelling related to slab-break off or magma emplacement in a subduction regime (Zhai and Santosh, 2011), mantle derived magmatism caused by ridge subduction(Santosh and Kusky, 2010; Guo et al., 2012) or magma underplating following continental collision (Yang et al., 2014). Metamorphic ages in the 1.95– 1.83 Ga range for granulite in the Daqingshan Complex may suggest long-term (>100 Ma) high-temperature exhumation during the late Paleoproterozoic (Wan et al., 2013b), although the exhumation histories vary spatially as indicated by the P–T paths (Fig. 9). The basement sample from the Yinchuan Basin evolved along a clockwise P–T path from the prograde stage through a peak of medium pressure granulite facies metamorphism to solidus conditions, most likely in one collision-burial-exhumation cycle. The basement of the Yinchuan Basin, as part of the western Khondalite Belt, should have been involved in the collision between the Yinshan and Ordos blocks at 1.96 Ga, and have undergone subsequent exhumation no later than 1.89 Ga, after a prolonged period of anatexis while resident in the middle crust. 9. Conclusions From the work presented above, it is evident that the Khondalite Belt has been subjected to an extended metamorphic history. Results of analysis on a basement sample obtained from beneath the Yinchuan Basin allow us to draw the following conclusions: (1) The basement beneath the Yinchuan Basin experienced granulite facies anatexis at P–T conditions of 6–10 kbar and 760–810°C, and retrogression to 4.5–5.5 kbar and 690–710°C, after which the partial melt finally crystallized. (2) NanoSIMS U–Pb analyses on zircon overgrowths yield a metamorphic age of 1895 ± 36 Ma. Temperatures calculated by Ti-in-zircon thermometry reveal the formation of metamorphic overgrowth during retrograde cooling. (3) Prograde monazite contains high Th, low Y and HREE, and has a concordia age of 1962 ± 8 Ma. Retrograde monazite has low Th, high Y and HREE and an age of 1892 ± 14 Ma. (4) The basement of the Yinchuan Basin is closely associated with exposed medium pressure granulites of the Khondalite Belt in terms of source material and metamorphic characteristics. The basement underwent a collision-burialexhumation cycle from 1.96 Ga to 1.89 Ga, accompanied by a ~70 Ma period of anatexis. Acknowledgements Prof. Yangting Lin, Dr. Jialong Hao, Jianchao Zhang and Lixu Deng are thanked for their help with isotopic analyses. Dr. W. Hastie is thanked for polishing the English of a draft of this manuscript. The study was financially supported by the National Natural Science Foundation of China (41202047, 41672062) and National Basic Research Program of China (2012CB416604). References Brown, M., 2007. Metamorphic conditions in orogenic belts: a record of secular change. Int. Geol. Rev. 49, 193–234. Cai, J., Liu, F.L., Liu, P.H., 2017. Paleoproterozoic multistage metamorphic events in Jining metapelitic rocks from the Khondalite Belt in the North China Craton: Evidence from petrology, phase equilibria modelling and U–Pb geochronology. J. Asian Earth Sci. 138, 515–534.

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Figure and Table Captions

Fig. 1. Geological sketch maps and simplified columnar section. (a), Geological sketch map of the North China Craton (modified after Zhao et al., 2005); (b),Tectonic subdivision of the Western Block (modified after Zhao et al., 2005; Wan et al., 2013a; Wang et al., 2014a); (c), Geological map for the Yinchuan Basin and adjoining region (modified after Huang et al., 2013); (d), Simplified columnar section for the borehole YC4. Fig. 2. Petrographical photographs showing typical textures and minerals of the basement sample Fig. 3. X-ray mapping and chemical profile of garnet grains Fig. 4. P–T pseudosections in the NCKFMASHTO system for the basement sample. (a), pseudosection for the bulk composition (SiO2 : 76.909; Al2O3: 9.577; CaO: 2.274; MgO: 1.780; FeO: 3.835; K2O: 1.044; Na2O: 4.062; TiO2: 0.299; O: 0.192; H2O: 3); (b), pseudosection for the local composition (SiO2: 70.12; Al2O3: 19.38; CaO: 0.18; MgO: 1.08; FeO: 3.22; K2O: 4.35; Na2O: 0.73; TiO2: 0.93; O: 0.01; H2O: 4); (c), garnet mode contour; (d), biotite mode contour; (e), sillimanite mode contour; (f), biotite composition contour, X(bi)= Fe2+/(Fe2++ Mg); (g), garnet composition contour, X(g) = Fe2+/(Fe2++ Mg), Z(g)= Ca/(Fe2++ Mg + Ca); (h), liquid (melt) mode contour; The contours for mineral mode and composition were drawn using the TCInvestigator (Pearce et al., 2015). Fig. 5. Cathodoluminescence (CL) images for representative zircons. Fig. 6. Diagrams for zircon U–Pb data. (a), concordia diagram for NanoSIMS data of metamorphic zircon overgrowths; (b), concordia diagram for LA-ICP-MS data of detrital zircon cores; (c), histogram for detrital zircon 207Pb/206Pb ages. Fig. 7. Back-scattered-electron (BSE) images for representative monazites. Fig. 8. U–Pb concordia diagrams and chondrite-normalized REE patterns for distinct monazite domains. (a), concordia diagram for bright gray domains; (b), concordia diagram for dark domains; (c), chondritenormalized REE patterns for bright gray domains; (d), chondritenormalized REE patterns for dark domains. Normalizing values of chondrite are from Sun and McDonough (1989). Fig. 9. P–T –t paths for granulites from the Khondalite Belt, North China Craton. (1), the MP garnet-sillimanite granulite (YC 4-1, this study); (2), the Helanshan HP garnet-kyanite-perthite granulite (Zhou et al., 2010); (3), the Qianlishan HP garnet-kyanite-K-feldspar granulite (Yin et al., 2014); (4), the Jining HP pelitic granulites (Wang et al., 2011); (5), the Jining MP garnetite (Jiao et al., 2013b); (6), the Daqingshan MP pelitic granulites (Cai et al., 2014); (7), the MP pelitic granulite from the northern margin of the Ordos Basin (Gou et al., 2016) ; (8), the Daqingshan sapphirine-bearing granulites (Guo et al., 2012); (9), the Jining sapphirine-bearing granulites (Santosh et al., 2009); (10), the Jining pelitic granulite (spinel-garnet gneiss, Li and Wei, 2016). The division of the granulite (G), ultrahigh-temperature granulite (UHTG) and eclogite-high-pressure granulite (E-HPG), and the effective sub-aluminous pelite solidus are after Brown (2007). Table 1. Microprobe analyses for garnet of the basement sample. Table 2. Microprobe analyses for biotite, plagioclase, K-feldsapr and muscovite of the basement sample. Table 3. NanoSIMS U–Pb isotopic data for metamorphic zircon overgrowths.

Table 4. LA-ICP-MS U–Pb isotopic data for detrital zircon cores. Table 5. LA-ICP-MS U–Pb isotopic data for distinct monazite domains. Table 6. Trace elements for distinct monazite domains.

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100 k m

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105 E

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38 N

40 N

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Xi’An

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Qianlishan

Helanshan

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Ordos Block

K h o n d a li

40 N

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TransNorth China Orogen

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(c)

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Paleogene Cretaceous

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39 ° 00′

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Quaternary

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Triassic

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Jurassic

Devonian

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l Ye

lo

w 38 ° 20′

Ganhegou Fm Hongliugou Fm Qingshuiying Fm Paleoproterozoic Cenozoic

an

Depth Lithology Age Fm (m)

540

1068

2177

4122

YC4-1

YC 4 Hole Sandstone 0

8

16km

Mudstone Metamorphic Unconformity Sampling location

105 ° 45′

38

106 ° 45′



00′



105

45′



Fig. 1

Fig. 2

a

1 cm

b

c

g

bi g

200 μm

200 μm

e

f

h

bi

200 μm

q

i

bi 200 μm

g

pl

bi

q

j

q

ksp sill

ksp

mu sill

20 μm

l

bi

q

sill

mu

q

g

200 μm

sill

sill bi

bi

sill

q

k

ab

ksp

mu

20 μm

ksp

pl

sill

200 μm

q

g

bi

bi

bi

sill

ksp

bi

pl

q

q

|

g

200 μm

g

q

q

bi

d

bi

20 μm

pl

m q

pl

pl

pl

pl pl 200 μm

ksp

pl

q 200 μm

q

a

Mg

Garnet 1

d

Mg

Garnet 2

B'

High1 Garnet

A

g

Mg

Garnet 3

High

GarnetHigh 2

C C' A'

Low

500 μm

b

Low

Low

B

500 μm

500 μm

Mn

Garnet 1

e

Mn

Garnet 2

B'

High

A

h

Mn

Garnet 3

High

High

C C' A'

Low

500 μm

94

c

Low

Low

B

500 μm

500 μm

f

Garnet 1

i

Garnet 2

Garnet 3 Alm

Py

Grs

Sps

Fe2+/(Fe2++Mg)

90 86 mol.%

82 78 20 16 12 8 4 0

rim A

core

rim rim A’ B

core

rim rim B’ C

core

Fig. 3

rim C’

750

800

P/ kbar

liq gs ill pl ilm

5

cd pl opx ilm liq

2

3

liq 1

NCKFMASHTO (+q)

(YC4-1)

(c)

11

g mode (mol.%) high low

10

ksp i

m li ksp il

O liq H 2 sp ilm bi sill pl l pl k p ilm liq il s i ksp ilm H2O b d ks sill c d pl 2 bi sill c ilm liq ksp H2O 3 sp ilm k l p l cd bi sil sill cd pl ksp ilm H2O

lm

pi

i gb

sill

s dk

liq

c

g sill cd ksp ilm liq

sill cd ksp ilm liq

4

700

750

800

850

900

T/ °C 12

NCKFMASHTO (+q)

(YC4-1)

(d)

11

10

bi mode (mol.%) high low

P/ kbar

6 8

7

5

4

4

3

3

2

2

700

750

800

850

900

13

2

6

5

1 650

4

8 10

4

7

2

8

6

P/ kbar

g sill ksp ilm liq

9

8

6

1 650

700

750

T/ °C NCKFMASHTO (+q)

(YC4-1)

(e)

12

NCKFMASHTO (+q)

900

(f)

11 10 9

6

P/ kbar

5

4

4

3

3

2

2

1 650

1 650

0.50

7

5

low

0.60

0.5

8 0.55

2.5

3.0

3.5

1.0

high

0.45

2.0

8

1.5

x(bi)

0.40

9

7

850

(YC4-1)

0.35

sill mode (mol.%) high low

10

6

800

T/ °C

11

P/ kbar

liq

10

9

12

ilm

bi sill mu pl ksp ilm liq H2O bi sill cd pl ksp ilm liq H2O sill cd pl ksp ilm liq H2O sill cd ksp ilm liq H2O

g bi sill ksp ilm liq

q

l pl

ksp

g bi sill mu ksp ilm liq

T/ °C 12

g

y bi k

1 2 3 4

g bi sill mu pl ksp ilm liq

sill m

bi sil

1 650

900

mu gb i ky

ill bi s

g cd pl opx ilm liq liq

4

850

(a) (b)

lm

liq lm

ilm sp

ill

ill c gs

6

g bi

ilm

iq ml p il l ks liq p ilm l ks

opx ilm

bi cd pl opx ilm liq

700

7

ksp u pl

up ill m

1 650

l g bi cd p

ky sill

8

i sil

sill

g bi ky mu ksp ilm

gb

bi

(YC4-1L)

ksp ilmg ky mu ksp ilm liq

bi s

c

liq

g bi cd pl ilm liq

O

cd pl ilm bi cbi cd p liq d pl l ilm opx liq ilm H2O liq H bi cd pl ilm H2O 2O sill

liq

H2

ilm

ilm

10

g cd pl ilm liq

liq

2

bi

l dp

s

g ky mu

11

g sill cd pl ilm liq g cd pl ksp ilm liq

g bi cd q ilm li pl ksp ilm liq

ilm pl cd bi

3

g bi

ksp

4

pl ill cd

gs

m

pl

5

g

liq

pl

p il l ks

6

m l pl il bi sil

ks

pi

ll p

d ll c i si

7

NCKFMASHTO (+q)

9 liq

liq

12

ill m u m p u pl l ks p ks il p ilm m H 2O

liq m pl il

(a)

g bi ky mu pl ksp ru ilm liq g ky mu pl ksp ru ilm liq g bi mu pl ksp ru ilm liq g bi ky mu pl ru ilm liq g bi ky pl ksp ru ilm liq

1 2 3 4 5

i si

mu

l

g ky p

5

pl ks pi lm

m

i ky gb

2O liq H l ilm sill p g bi H 2O l ilm sill p H2O g bi pl ilm ill cd g bi s

P/ kbar

q

m li

il u pl

gb

8

g bi

1

liq

ilm ksp ru

gb

9

2O liq H l ilm mu p 2O pl ilm H g bi mu 2O u pl ilm H g bi ky m

10

3 2 4

g bi

11

(YC4-1)

g bi mu pl ru ilm liq

dp lk

liq H2O pl ru ilm g bi mu u pl ru ilm liq g bi m

bi s

NCKFMASHTO (+q)

gb i ky

12

0.65

x(bi)=Fe2+/(Fe2++Mg)

700

750

800

T/ °C

850

900

700

750

800

850

T/ °C

Fig. 4 a-f

900

(YC4-1)

(g)

0

0.05

P/ kbar

0.66

0.74

0.80

A

C

10

0.04

9

0.03

0.02

0.86

6 5

0.78

0.84

7

0.82

8

0.70

9

z(g)

B

8

A

7 10

7

0.0

liq mode (mol.%) high low

8

10

(YC4-1)

(h)

11

x(g)

0 0.1

NCKFMASHTO (+q)

6

11

12

4

.15

2

NCKFMASHTO (+q)

P/ kbar

12

6 5

4

4

3

3

C

B

20

2 1 650

x(g)=Fe2+/(Fe2++Mg) z(g)=Ca/(Fe2++Mg+Ca)

700

750

800

T/ °C

850

900

30

2 1 650

700

750

800

850

T/ °C

Fig. 4 g-h

900

(b) 1835.4 ± 34.0 Ma

50 μm

(c)

1846.3 ± 27.4 Ma

(d)

1864.8 ± 21.3 Ma

23

(a)

(i)

1856.8 ± 17.2 Ma

1813.7 ± 11.0 Ma

(j)

1829.2 ± 17.9 Ma

1877.7 ± 17.1 Ma

(g)

(k)

1810.3 ± 21.8 Ma

(h)

1855.9 ± 24.2 Ma

(l)

1837.3 ± 54.9 Ma

(f)

(e)

1900.7 ± 25.3 Ma

1827.1 ± 77.4 Ma

Fig. 5

0.5

(a) metamorphic rim

2200

NanoSIMS

1800

0.3

Upper intercept 1895 ± 36 Ma MSWD = 0.66, n = 13

1400

0.2

1000

box heights are 2σ

2000 207Pb/ 206Pb

206Pb/238U

0.4

1900

0.1 600

1800 1700 1600

0.0

0

2

Mean = 1840 ± 17 Ma MSWD = 1.9, n = 13

4

6

8

10

207Pb/235U

(b)

0.5

2800

detrital core

2400

LA-ICP-MS

206Pb/238U

0.4 2000

0.3

1600

concordant 207Pb/206Pb ages (red solid ellipses, n = 56)

0.2 1200

2005 ± 32 Ma – 2432 ± 40 Ma 0.1

1

3

5

7

9

11

13

15

207Pb/235U

20 18

(c)

inherited core LA-ICP-MS n=56

16

Number

Relative probability

14 12 10 8 6 4 2

0 1800 1900 2000 2100 2200 2300 2400 2500 2600 2700 207Pb/206Pb

age/Ma

Fig. 6

(a)

80 μm

(b)

1891 ± 32.9 Ma

(c)

1924 ± 60.0 Ma

(d)

1909 ± 29.6 Ma

1869 ± 29.9 Ma

1943 ± 63.0 Ma 1947 ± 48.3 Ma

(e)

(f)

1907 ± 35.0 Ma

1924 ± 36.6 Ma

1944 ± 55.4 Ma

1943 ± 57.4 Ma

1894 ± 35.7 Ma

(g)

1983 ± 50.0 Ma

(h) 1910 ± 33.0 Ma

1922 ± 58.2 Ma

1874 ± 39.0 Ma

1961 ± 54.3 Ma

Fig. 7

(a)

2200

monazite (bright gray domain)

0.40

1000000

monazite (bright gray domain) (c)

206Pb/238U

0.36

1800

0.32

Concordia age 1962 ± 8.0 Ma MSWD = 0.24, n = 13

1600

0.28

Monazite/Chondrite

100000 2000

1000 100 10 0

1400

0.24 2.5

10000

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 3.5

4.5

5.5

6.5

7.5

207Pb/235U

(b)

2200

monazite (dark domain)

0.40

1000000

monazite (dark domain) (d)

206Pb/238U

0.36

1800

0.32

Intercepts at 1892 ± 14 Ma MSWD = 0.88, n = 30

1600

0.28

10000 1000 100 10 0

1400

0.24 2.5

Monazite/Chondrite

100000 2000

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 3.5

4.5

5.5

6.5

7.5

207Pb/235U

Fig. 8

s (pelitic d solidu aturate water s

15 14 13 12

/km °C

20

YC4-1)

10 9 8

Ga 96 1.

7 6 K Sil y l

P / kbar

11

E-HPG

5

4

5 6 1

/km

8

7

G

3

Sill And

3

9

Ga 1.89

2

Ky And

4

40°C

10

UHTG

Effective sub-aluminous pelite solidus

2 1 400

500

600

700

800

900

1000

1100

1200

T / °C

Fig. 9

Table 1

Mineral Garnet 1 Garnet 2 Garnet 3 Spot 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 3.1 3.2 3.3 3.4 3.5 3.6 3.7 SiO2 36.87 37.02 36.74 36.82 36.78 36.82 36.82 36.75 36.58 36.95 36.70 36.93 36.88 37.28 36.84 36.71 37.46 37.37 36.79 36.76 37.10 37.42 37.53 37.51 36.82 36.94 36.99 TiO2 0.02 0.00 0.00 0.00 0.01 0.01 0.03 0.00 0.00 0.05 0.05 0.05 0.06 0.05 0.00 0.02 0.02 0.00 0.03 0.05 0.01 0.00 0.00 0.00 0.01 0.00 0.05 Al 2 O3 20.86 21.01 20.56 20.81 20.64 20.66 20.82 20.52 20.68 20.80 20.50 20.82 20.63 21.05 20.94 20.58 21.06 21.16 20.76 20.42 20.75 21.45 20.91 20.90 20.53 20.81 20.82 Cr2 O3 0.06 0.02 0.03 0.05 0.07 0.03 0.03 0.00 0.04 0.02 0.04 0.06 0.02 0.05 0.05 0.03 0.03 0.06 0.05 0.07 0.00 0.01 0.02 0.08 0.02 0.10 0.00 Fe 2O3 0.00 0.00 0.00 0.00 0.75 0.00 0.74 0.63 0.56 0.10 0.04 0.00 0.00 0.09 0.58 0.50 0.10 0.34 0.71 0.19 1.19 0.43 0.68 0.77 0.83 0.43 0.70 FeO 37.40 37.27 37.63 37.44 37.39 37.38 36.02 36.98 37.30 37.88 37.70 36.74 37.18 37.44 36.57 36.99 37.03 36.98 36.68 37.52 35.85 35.60 36.04 35.54 37.35 35.94 35.28 MnO 1.57 1.14 1.01 0.97 1.05 1.05 0.88 0.90 1.18 1.56 1.56 1.12 0.98 0.97 0.87 1.02 0.92 0.93 0.98 1.46 0.57 0.63 0.64 0.70 0.70 0.63 0.66 MgO 2.04 2.53 2.15 2.44 2.42 2.45 3.20 2.82 2.38 2.00 2.02 2.70 2.75 2.88 3.03 2.77 3.16 3.20 3.01 2.20 3.87 4.16 3.96 4.21 2.77 3.73 4.09 CaO 0.80 0.79 0.84 0.83 0.81 0.76 0.80 0.74 0.78 0.84 0.78 0.82 0.73 0.72 0.79 0.74 0.78 0.74 0.73 0.69 0.79 0.73 0.81 0.74 0.70 0.74 0.74 Na2 O 0.01 0.00 0.05 0.00 0.04 0.01 0.09 0.01 0.00 0.02 0.01 0.03 0.01 0.03 0.04 0.00 0.04 0.01 0.01 0.03 0.00 0.02 0.00 0.00 0.03 0.00 0.02 K2 O 0.01 0.02 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.02 0.00 0.02 0.01 0.02 0.03 0.05 0.00 0.00 0.00 Totals 99.64 99.80 99.01 99.36 99.88 99.17 99.35 99.30 99.45 100.22 99.40 99.27 99.24 100.56 99.65 99.31 100.60 100.78 99.68 99.39 100.02 100.43 100.55 100.42 99.68 99.27 99.28 1 Oxygens 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 3.005 3.002 3.012 3.002 2.989 3.009 2.986 2.996 2.986 3.000 3.006 3.006 3.007 2.997 2.984 2.993 3.003 2.991 2.983 3.007 2.981 2.982 2.996 2.994 2.992 2.991 2.986 Si Ti 0.001 0.000 0.000 0.000 0.001 0.001 0.002 0.000 0.000 0.003 0.003 0.003 0.004 0.003 0.000 0.001 0.001 0.000 0.002 0.003 0.001 0.000 0.000 0.000 0.001 0.000 0.003 Al 2.004 2.009 1.987 2.001 1.977 1.990 1.991 1.972 1.990 1.991 1.979 1.998 1.983 1.995 2.000 1.978 1.991 1.997 1.985 1.969 1.966 2.015 1.968 1.967 1.967 1.986 1.982 Cr 0.004 0.001 0.002 0.003 0.004 0.002 0.002 0.000 0.003 0.001 0.003 0.004 0.001 0.003 0.003 0.002 0.002 0.004 0.003 0.005 0.000 0.001 0.001 0.005 0.001 0.006 0.000 Fe3+ 0.000 0.000 0.000 0.000 0.046 0.000 0.045 0.039 0.035 0.006 0.003 0.000 0.000 0.006 0.035 0.030 0.006 0.021 0.043 0.012 0.072 0.026 0.041 0.046 0.051 0.026 0.043 Fe2+ 2.549 2.528 2.580 2.553 2.541 2.555 2.443 2.521 2.547 2.572 2.582 2.501 2.535 2.518 2.478 2.523 2.483 2.476 2.487 2.567 2.409 2.373 2.407 2.372 2.539 2.433 2.382 Mn 0.108 0.078 0.070 0.067 0.072 0.073 0.060 0.062 0.082 0.107 0.108 0.077 0.068 0.066 0.060 0.070 0.062 0.063 0.067 0.101 0.039 0.043 0.043 0.047 0.048 0.043 0.045 Mg 0.248 0.306 0.263 0.297 0.293 0.298 0.387 0.343 0.290 0.242 0.247 0.328 0.334 0.345 0.366 0.337 0.378 0.382 0.364 0.268 0.463 0.494 0.471 0.501 0.335 0.450 0.492 Ca 0.070 0.069 0.074 0.073 0.071 0.067 0.070 0.065 0.068 0.073 0.068 0.072 0.064 0.062 0.069 0.065 0.067 0.063 0.063 0.060 0.068 0.062 0.069 0.063 0.061 0.064 0.064 Na 0.002 0.000 0.008 0.000 0.006 0.002 0.014 0.002 0.000 0.003 0.002 0.005 0.002 0.005 0.006 0.000 0.006 0.002 0.002 0.005 0.000 0.003 0.000 0.000 0.005 0.000 0.003 0.001 0.002 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.000 0.002 0.001 0.002 0.003 0.005 0.000 0.000 0.000 K Cation 7.991 7.994 7.997 7.996 8.000 7.995 8.000 8.000 8.000 8.000 8.000 7.993 7.998 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 X(g) 0.911 0.892 0.907 0.896 0.897 0.896 0.863 0.880 0.898 0.914 0.913 0.884 0.884 0.879 0.871 0.882 0.868 0.866 0.872 0.905 0.839 0.828 0.836 0.826 0.883 0.844 0.829 Z(g) 0.024 0.024 0.025 0.025 0.024 0.023 0.024 0.022 0.023 0.025 0.023 0.025 0.022 0.021 0.024 0.022 0.023 0.022 0.022 0.021 0.023 0.021 0.023 0.021 0.021 0.022 0.022 Grs 0.024 0.023 0.025 0.024 0.024 0.022 0.024 0.022 0.023 0.024 0.023 0.024 0.021 0.021 0.023 0.022 0.022 0.021 0.021 0.020 0.023 0.021 0.023 0.021 0.020 0.021 0.021 Sps 0.036 0.026 0.023 0.022 0.024 0.024 0.020 0.021 0.027 0.036 0.036 0.026 0.023 0.022 0.020 0.023 0.021 0.021 0.022 0.034 0.013 0.014 0.014 0.016 0.016 0.014 0.015 Py 0.083 0.103 0.088 0.099 0.098 0.100 0.131 0.115 0.097 0.081 0.082 0.110 0.111 0.115 0.123 0.113 0.126 0.128 0.122 0.089 0.155 0.166 0.158 0.168 0.112 0.151 0.165 Alm 0.857 0.848 0.864 0.854 0.854 0.854 0.825 0.843 0.853 0.859 0.859 0.840 0.845 0.842 0.834 0.842 0.830 0.830 0.834 0.857 0.809 0.798 0.805 0.795 0.851 0.814 0.799

Table 2 Mineral SiO2 TiO2 Al2 O3 Cr2 O3 Fe2 O3 FeO MnO MgO CaO Na2 O K2 O Totals Oxygens Si Ti Al Cr 3+ Fe Fe 2+ Mn Mg Ca Na K Cation X(bi)

bi bi 34.54 2.68 18.95 0.29 0.00 23.01 0.04 6.83 0.07 0.14 9.75 96.31 11 2.660 0.155 1.720 0.018 0.000 1.482 0.003 0.784 0.006 0.021 0.958 7.806 0.654

bi bi 35.11 2.33 18.29 0.13 0.00 22.76 0.02 7.08 0.00 0.07 10.06 95.86 11 2.714 0.135 1.667 0.008 0.000 1.471 0.001 0.816 0.000 0.010 0.992 7.815 0.643

bi bi 33.82 2.33 19.42 0.14 0.00 21.25 0.04 7.33 0.00 0.11 9.52 93.97 11 2.647 0.137 1.792 0.009 0.000 1.391 0.003 0.855 0.000 0.017 0.950 7.800 0.619

bi bi 33.85 2.20 18.88 0.27 0.00 21.63 0.03 7.32 0.02 0.11 9.78 94.10 11 2.658 0.130 1.748 0.017 0.000 1.420 0.002 0.856 0.002 0.017 0.980 7.829 0.624

bi bi 34.98 1.86 18.91 0.19 0.00 21.94 0.00 7.70 0.04 0.15 9.77 95.55 11 2.697 0.108 1.719 0.012 0.000 1.415 0.000 0.885 0.003 0.022 0.961 7.822 0.615

bi bi 34.74 2.00 18.84 0.12 0.00 22.24 0.00 7.52 0.02 0.08 9.76 95.33 11 2.690 0.116 1.720 0.007 0.000 1.440 0.000 0.868 0.002 0.012 0.964 7.819 0.624

ksp 48.28 0.48 36.23 0.00 1.37 0.00 0.00 0.45 0.03 0.20 7.86 94.91 8 2.288 0.017 2.024 0.00 0.049 0.00 0.00 0.032 0.001 0.018 0.475 4.905

ksp 49 0.4 36.83 0.00 1.34 0.00 0.01 0.5 0.05 0.16 7.29 95.58 8 2.295 0.014 2.033 0.00 0.047 0.00 0.00 0.035 0.003 0.015 0.436 4.877

mu 48.27 0.28 36.43 0.00 0.94 0.36 0.00 0.55 0.00 0.27 8.52 95.64 11 3.137 0.014 2.791 0.00 0.046 0.02 0.00 0.053 0.00 0.034 0.706 6.802 An Ab Or

pl fsp 61.46 0.02 23.13 0.02 0.01 0.00 0.00 0.00 4.75 9.41 0.21 99.01 8 2.759 0.001 1.224 0.001 0.000 0.000 0.000 0.000 0.228 0.819 0.012 5.044 21.53 77.34 1.13

pl fsp 63.25 0.00 23.15 0.01 0.02 0.00 0.03 0.00 4.38 9.73 0.15 100.72 8 2.784 0.000 1.201 0.000 0.001 0.000 0.001 0.000 0.207 0.831 0.008 5.034 19.79 79.45 0.76

pl fsp 63.03 0.05 22.95 0.03 0.07 0.00 0.00 0.00 4.51 9.83 0.17 100.64 8 2.781 0.002 1.194 0.001 0.002 0.000 0.000 0.000 0.213 0.841 0.010 5.044 20.02 79.04 0.94

pl fsp 62.15 0.07 22.24 0.01 0.57 0.00 0.01 0.01 3.75 10.18 0.21 99.20 8 2.787 0.002 1.176 0.000 0.019 0.000 0.000 0.001 0.180 0.885 0.012 5.062 16.71 82.17 1.11

pl fsp 63.35 0.03 23.11 0.04 0.01 0.00 0.03 0.00 4.48 9.33 0.23 100.61 8 2.789 0.001 1.200 0.001 0.000 0.000 0.001 0.000 0.211 0.797 0.013 5.014 20.67 78.06 1.27

pl fsp 62.89 0.06 23.10 0.00 0.02 0.00 0.03 0.00 4.45 9.69 0.20 100.44 8 2.779 0.002 1.203 0.000 0.001 0.000 0.001 0.000 0.211 0.830 0.011 5.038 20.06 78.90 1.05

pl fsp 62.87 0.04 23.03 0.02 0.06 0.00 0.02 0.00 4.71 9.65 0.24 100.64 8 2.776 0.001 1.199 0.001 0.002 0.000 0.001 0.000 0.223 0.826 0.014 5.042 20.98 77.70 1.32

Table 3. Isotopic ratios Spot

207

Pb/206 Pb 1σ (±%)

207

Pb/235 U 1σ (±%)

Age (Ma) 206

Pb/238U 1σ (±%)

206

Pb/238U Age

1σ

207

Pb/235 U Age

1σ

207

Pb/206 Pb Age

1σ

% Discordance

1

0.11114

1.25

3.74098

4.68

0.2441

4.51

1408.1

57.2

1580.2

38.2

1818.1

22.5

-25

2

0.11182

1.00

3.71167

5.55

0.2407

5.46

1390.5

68.7

1573.9

45.4

1829.2

17.9

-27

3

0.11288

1.53

4.28360

7.13

0.2752

6.96

1567.3

97.6

1690.2

60.4

1846.3

27.4

-17

4

0.11404

1.19

3.86836

4.67

0.2460

4.52

1417.9

57.7

1607.1

38.4

1864.8

21.3

-27

5

0.11486

0.95

4.99560

6.60

0.3154

6.53

1767.4

101.8

1818.6

57.4

1877.7

17.1

-7

6

0.11354

0.96

4.22628

4.19

0.2700

4.08

1540.6

56.2

1679.1

35.0

1856.8

17.2

-19

7

0.11066

1.21

3.87696

3.92

0.2541

3.73

1459.6

48.9

1608.9

32.1

1810.3

21.8

-22

8 9

0.11348 0.11169

1.35 4.38

4.26750 2.83585

3.66 10.28

0.2727 0.1841

3.41 9.30

1554.7 1089.6

47.2 93.9

1687.1 1365.1

30.6 80.3

1855.9 1827.1

24.2 77.4

-18 -44

10

0.11087

0.61

3.39806

3.47

0.2223

3.41

1294.0

40.1

1503.9

27.6

1813.7

11.0

-32

11

0.11634

1.42

4.47160

6.46

0.2788

6.30

1585.1

89.2

1725.7

55.1

1900.7

25.3

-19

12

0.11232

3.09

4.19174

12.23

0.2707

11.84

1544.2

164.6

1672.4

105.6

1837.3

54.9

-18

13

0.11220

1.90

4.25006

6.64

0.2747

6.36

1564.8

88.9

1683.7

56.1

1835.4

34.0

-17

Table 4 Sp Pb Th ot pp pp m m 1 28 12 0 16 4 2 40 2 7 30 11 3 1 10 4 4 21 9 9 5 28 11 2 52. 6 6 11

Pb/20 207Pb/ 23 6 5 Pb U 1σ Ratio

Pb/23 206Pb/ 23 5 8 U U 1σ Ratio

9 97. 1 12 2 10 9 83. 7 10 1 19 0 40. 5 20 7 12

7 31 7 31 8 13 7 19 6 17

2 43 9 14 0 23. 5 80.

4 52 2 20 2 20 4 15

Pb/23 U 1σ

8

207

Pb/20 6 Pb Age

207

6

Pb/20 Pb 1σ

207

Pb/ 23 5 U Age

207

Pb/23 U 1σ

5

206

Pb/ 23 8 U Age

206

Pb/23 Concorda U nce 1σ %

8

2102 2066 1949 2094 2233 2082

15.8 15.0 15.3 17.1 19.2 20.7

2092 2002 1881 2084 2223 2072

19.0 18.2 17.2 19.5 25.3 24.1

99 96 95 99 99 99

0.2283 0.4586 0.0063 0.1301 0.3806 0.0046

2432 2039

40.1 33.3

2437 2066

21.1 17.3

2433 2079

27.9 21.3

99 99

0.1030 0.3457 0.0032 0.1436 0.3792 0.0046

2059 2094

27.9 33.5

1992 2091

14.8 18.7

1914 2073

15.6 21.6

95 99

6.2939 6.9475 6.5245 7.4109

0.1223 0.1411 0.1396 0.1435

0.3643 0.3822 0.3783 0.3939

0.0036 0.0047 0.0057 0.0049

2020 2109 2021 2169

34.7 31.6 36.6 29.8

2018 2105 2049 2162

17.1 18.1 18.9 17.4

2002 2087 2069 2141

17.0 22.0 26.7 22.9

99 99 99 99

0.1518 0.1028 0.1288 0.1194

0.3802 0.3010 0.3819 0.3773

0.0053 0.0027 0.0044 0.0042

2073 2118 2080 2033

38.0 33.0 31.5 32.2

2082 1903 2090 2050

19.9 16.1 16.8 16.2

2077 1696 2085 2064

24.6 13.6 20.7 19.5

99 88 99 99

4 12 4 38. 0 11 6 10 5 15 8 31 7 34 1 21 4 27 5 41 1 61. 8 22 4 16 4 5 7 12 57. 11 4 57. 3 95. 7 13 7 19 3 27 0 37

0.1282 0.0028 6.7691 0 0.1315 0.0025 5.5128 0.8 4 0.1287 0.0023 6.8326 0.6 9 0.1246 0.0023 6.5290 0.1 2 0.5 0.1320 0.0026 7.0595 2 0.1360 0.0027 7.2697 0.3 0 0.1402 0.0030 8.0939 0.9 2 0.1328 0.0025 7.0632 0.4 9 0.1393 0.0027 7.4036 0.7 9 0.1315 0.0022 6.8632 0.2 7 0.1295 0.0026 6.7792 0.4 9 0.1330 0.0031 7.1484 0.6 0 0.1323 0.0024 5.7145 0.6

0.1369 0.1770 0.1802 0.1385 0.1521

0.3848 0.3837 0.4147 0.3823 0.3819

0.0042 0.0063 0.0048 0.0044 0.0045

2124 2177 2231 2135 2220

29.2 35.3 70.5 33.2 33.3

2119 2145 2242 2119 2161

17.3 21.8 20.2 17.5 18.4

2099 2094 2236 2087 2085

19.7 29.3 21.7 20.8 20.8

99 97 99 98 96

0.1167 0.1319 0.1912 0.1342

0.3755 0.3777 0.3871 0.3103

0.0035 0.0038 0.0063 0.0049

2118 2092 2139 2129

29.3 35.2 46.5 31.3

2094 2083 2130 1934

15.1 17.3 23.9 20.3

2055 2066 2110 1742

16.7 18.0 29.5 24.0

98 99 99 89

6 72. 3 17 6 20 1 13 1 63 0

0.1571 0.1417 0.1478 0.1368 0.1217

0.3841 0.3839 0.3836 0.3724 0.3819

0.0050 0.0043 0.0048 0.0057 0.0033

2128 2128 2120 2006 2057

32.4 32.9 34.4 38.7 31.5

2116 2118 2111 2023 2076

19.9 17.9 18.8 19.0 16.1

2096 2095 2093 2041 2085

23.3 19.9 22.5 26.9 15.4

99 98 99 99 99

8 97. 4 12 9 14 8 15 1 39 7

9 0.2 6 0.6 3 0.6 4 0.3 7 0.8 4

Sp Pb Th ot pp pp m m 33 34 16 8 39. 4 34 92 3 35 14 66. 3 66. 7 36 15 6 7 24 11 37 1 73. 4 38 15

U pp m 28 6 81. 3 12 6 18 2 13 2 13

4 27 8 21 1 29 0 18 7 43 18 0 44 62. 5 45 18 3 46 33 20 47 3

6 15 9 91. 0 12 4 80. 5 75.

0.0024 0.0024 0.0025 0.0023

7.0395 7.0483 6.9990 6.3303 6.7256

0.3834 0.3642 0.3389 0.3817 0.4117 0.3791

206

29.3 28.2 30.7 33.3 37.0 41.7

0.1243 0.1307 0.1244 0.1354

0.0022 0.0022 0.0021 0.0024 0.0030 0.0030

207

0.1232 0.1123 0.1020 0.1322 0.1701 0.1578

5 0.3 2 0.6 0 0.3 0 1.0 6 0.7

0.1299 0.1313 0.1233 0.1292 0.1400 0.1287

207

6.9253 6.6465 5.8158 6.8629 8.0137 6.7742 1 1.3 4 0.1578 0.0038 10.020 69. 6 0.8 9 0.1257 0.0024 6.6516 9 14 2 0.3 6 0.1271 0.0021 6.1127 28 7 0.4 8 0.1297 0.0025 6.8404 18

2 24. 9 81. 0 94. 4 56. 2 33 3

28 29 30 31 32

Pb/20 6 Pb Ratio

2096 2115 2006 2088 2228 2081

5 22 6 24 0 9 23 0 10 19 5 11 24 9 12 41 10 13 0 7 14 39 9 15 26 6 16 66 6 17 28 97. 18 2 2 19 16 7 20 11 1 21 22

24 25 26 27

207

0.0041 0.0038 0.0036 0.0042 0.0055 0.0051

7 8

22 23

U Th/ U pp m 24 0.5 2 0.4 1 41 7 0.2 0 45 7 0.7 5 14 0 8 21 0.5 3 0.5 5 97.

0.1322 0.1323 0.1315 0.1233 0.1270

0.0028 0.0024 0.0025 0.0027 0.0023

Th/ U

207

207

6

6

0.5 7 0.4 8 0.5 3 0.3 7 0.8 7 0.5

0.1252 0.0026 6.6097 0.1503 0.3810 0.0048 0.1283 0.0029 6.8132 0.1643 0.3839 0.0050 0.1246 0.1264 0.1296 0.1262

0.0025 0.0022 0.0024 0.0024

6.5347 6.7385 6.9103 6.6913

0.1390 0.1248 0.1390 0.1433

0.3783 0.3842 0.3839 0.3819

4 27 4 16 1 31 0 14 8 19

5 0.5 8 0.5 7 0.4 0 0.5 4 0.3

0.1320 0.1349 0.1295 0.1372

0.0024 0.0027 0.0021 0.0025

5.9646 7.2834 6.8911 7.7519

0.1393 0.1630 0.1388 0.1359

4 21. 8 74. 0 13 9 96.

8 90. 4 24 0 33 5 13

8 0.2 4 0.3 1 0.4 1 0.7

0.1294 0.1289 0.1288 0.1313

0.0023 0.0025 0.0024 0.0026

6.9203 6.8950 6.8895 6.9957

0.1219 0.1437 0.1322 0.1511

2 33. 1 48 10 0 3 34 16 49 0 50. 6 50 12 3 15 1 51 37

7 14 4 20 7 15 6 39

0 0.2 3 0.8 0 0.3 2 0.3

0 15 4 52 32 0 22 4 53 45 2 5

Table 4 (continued)

39 40 41 42

Pb/20 Pb Ratio

Pb/20 207Pb/ 23 5 Pb U 1σ Ratio

207

Pb/23 206Pb/ 23 8 U U 1σ Ratio

207

207

6

6

Pb/ 23 U Age

2032 2076

36.7 40.7

2061 2087

20.1 21.4

2081 2094

22.5 23.5

99 99

0.0042 0.0036 0.0046 0.0053

2033 2050 2094 2046

35.2 31.2 31.8 33.5

2051 2078 2100 2071

18.8 16.4 17.9 19.0

2068 2096 2094 2085

19.9 17.0 21.4 24.6

99 99 99 99

0.3240 0.3885 0.3821 0.4071

0.0051 0.0060 0.0052 0.0048

2125 2165 2090 2192

37.2 35.0 29.5 36.3

1971 2147 2098 2203

20.4 20.0 17.9 15.8

1809 2116 2086 2202

24.7 27.7 24.2 22.1

91 98 99 99

0.3848 0.3852 0.3845 0.3827

0.0040 0.0049 0.0041 0.0046

2100 2083 2083 2117

31.2 33.2 31.9 35.0

2101 2098 2097 2111

15.7 18.5 17.1 19.2

2099 2100 2097 2089

18.6 23.0 19.1 21.5

99 99 99 98

0.1329 0.0026 7.2063 0.1348 0.3906 0.0046 0.1288 0.0027 6.9068 0.1542 0.3861 0.0058 0.1343 0.0026 7.1678 0.1409 0.3848 0.0056

2139 2083 2155

34.7 31.0 33.3

2137 2100 2133

16.7 19.9 17.6

2126 2105 2099

21.3 26.9 26.0

99 99 98

0.1234 0.0022 6.4302 0.1173 0.3753 0.0042 0.1316 0.0023 7.1137 0.1516 0.3885 0.0059

2005 2120

31.5 31.0

2036 2126

16.1 19.0

2054 2116

19.8 27.3

99 99

8 0.6 9 0.1318 0.0022 7.0485 0.1226 0.3851 0.0043 25 2 0.5 1 0.1241 0.0020 6.2273 0.1004 0.3616 0.0038 45 0 0

2122 2017

28.2 28.5

2118 2008

15.5 14.2

2100 1990

20.1 17.8

99 99

5

206

Pb/23 U 1σ

8

Pb/20 Pb Age

Pb/20 Pb 1σ

207

5

207

Pb/23 U 1σ

5

206

Pb/ 23 U Age 8

206

Pb/23 Concorda U nce 1σ %

8

54 15 59. 0 82. 0 55 21 0 7 56 13 56. 1 50. 8 57 11 7 9 41 33 58 3 50. 9 59 12 9 4 60 81. 28.

1 13 7 61 33 6 7 62 20 97. 9 2

17 0.3 0.1313 5 0.3 4 0.1276 27 1 0.5 0 10 0.1364 7 0.4 3 0.1259 11 0 0.9 6 0.1283 34 7 0.3 8 0.1281 13 8 6 0.1280 10 0.2 2 0.5 8 0.1355 27 5 0.7 0 13 0.1342 7 1

0.0024 7.0232 0.1435 0.3847 0.0045 0.0020 6.3854 0.1094 0.3609 0.0044

2117 2065

32.1 27.8

2114 2030

18.2 15.1

2098 1986

21.2 20.7

99 97

0.0025 0.0024 0.0023 0.0025 0.0024

0.0063 0.0046 0.0063 0.0048 0.0052

2181 2043 2076 2073 2072

31.945 33.3 31.8 33.6 34.4

2190 2073 1876 2085 2086

20.8 18.0 24.9 17.1 18.2

2186 2093 1671 2093 2092

28.9 21.4 31.6 22.2 24.1

99 99 88 99 99

0.0021 7.7242 0.1203 0.4103 0.0035

2170

27.9

2199

14.1

2216

16.2

99

0.0023 7.1775 0.1360 0.3853 0.0054

2153

29.6

2134

17.0

2101

25.1

98

7.6444 6.6998 5.3442 6.7980 6.8010

0.1763 0.1361 0.1555 0.1308 0.1395

0.4036 0.3835 0.2960 0.3835 0.3834

U 207Pb/ 206 Pb Spot Spot Pb Ratio size ppm ppm analyses for the bright gray domains 1 10 8318 4435 0.1187 2 10 8270 1986 0.1179 3 10 8165 2628 0.1173 4 10 8807 2093 0.1225 5 10 6822 2044 0.1171 6 10 10309 2408 0.1191 7 10 10600 2605 0.1144 8 10 8171 2347 0.1191 9 10 10989 2930 0.1218 10 10 8926 2174 0.1203 11 10 8029 2304 0.1193 12 10 7895 1821 0.1192 13 10 8673 2119 0.1190 analyses for the dark domains 1 16 5745 2795 0.1146 2 16 5535 2088 0.1158 3 16 5003 2677 0.1178 4 16 7033 7053 0.1141 5 16 5249 2914 0.1157 6 16 6098 1985 0.1144 7 16 6295 10858 0.1173 8 16 6541 4841 0.1169 9 16 6992 10441 0.1176 10 16 5078 1843 0.1206 11 16 6178 1358 0.1168 12 16 5702 2130 0.1181 13 16 4983 1949 0.1188 14 16 4403 1945 0.1179 15 16 5204 1747 0.1161 16 16 7030 5597 0.1171 17 16 6626 6775 0.1143 18 16 4789 2207 0.1149 19 16 5024 1794 0.1146 20 16 5343 2928 0.1170 21 16 6655 1740 0.1175 22 16 5197 1923 0.1159 23 16 4798 2444 0.1184 24 16 5105 1865 0.1148 25 16 4718 2658 0.1179 26 16 5836 2594 0.1186 27 16 5302 2171 0.1175 28 16 5464 2148 0.1203 29 16 5440 2625 0.1199 30 16 5218 2272 0.1190

207

Pb/206Pb 1σ

207

Pb/235U Ratio

207

Pb/235U 1σ

206

Pb/238U Ratio

206

Pb/238U 1σ

207

Pb/206Pb Age

207

Pb/206 Pb 1σ

207

Pb/ 235U Age

207

Pb/ 235U 1σ

206

Pb/ 238 U Age

206

Pb/ 238 U Concordance 1σ %

0.0032 0.0036 0.0034 0.0042 0.0038 0.0037 0.0039 0.0042 0.0034 0.0037 0.0033 0.0038 0.0038

6.0743 5.7612 5.8628 6.0216 5.6928 5.8987 5.6358 5.8828 5.9437 6.0279 6.1223 6.0025 5.8528

0.1925 0.1778 0.1755 0.2406 0.1802 0.2103 0.2072 0.2132 0.1800 0.2039 0.1922 0.2005 0.2033

0.3652 0.3510 0.3592 0.3545 0.3548 0.3530 0.3515 0.3549 0.3502 0.3579 0.3679 0.3634 0.3529

0.0087 0.0072 0.0076 0.0103 0.0086 0.0087 0.0090 0.0095 0.0085 0.0086 0.0091 0.0088 0.0086

1939 1924 1917 1994 1922 1944 1872 1943 1983 1961 1947 1944 1943

48.1 60.0 52.9 61.3 58.2 55.4 61.0 63.0 50.0 54.3 48.3 89.8 57.4

1987 1941 1956 1979 1930 1961 1922 1959 1968 1980 1993 1976 1954

28 27 26 35 27 31 32 31 26 29 27 29 30

2007 1939 1978 1956 1958 1949 1942 1958 1936 1972 2020 1998 1948

41 35 36 49 41 41 43 45 41 41 43 42 41

98 99 98 98 98 99 98 99 98 99 98 98 99

0.0025 0.0023 0.0022 0.0018 0.0021 0.0023 0.0020 0.0019 0.0017 0.0021 0.0023 0.0024 0.0023 0.0024 0.0023 0.0018 0.0019 0.0023 0.0025 0.0021 0.0022 0.0021 0.0021 0.0023 0.0022 0.0021 0.0020 0.0020 0.0019 0.0021

5.3881 5.3204 5.3367 5.3297 5.3231 5.2228 5.5177 5.3519 5.4419 5.3660 5.2528 5.4618 5.3933 5.4293 5.2515 5.4704 5.3199 5.3232 5.2831 5.3968 5.5972 5.2322 5.2336 5.1467 5.3194 5.3499 5.3893 5.4722 5.5008 5.3577

0.1168 0.1055 0.0988 0.0843 0.0950 0.1052 0.0946 0.0879 0.0788 0.0928 0.1047 0.1142 0.1094 0.1050 0.1019 0.0840 0.0870 0.1062 0.1127 0.0964 0.1037 0.0924 0.0939 0.1021 0.0978 0.0958 0.0938 0.0874 0.0860 0.0899

0.3411 0.3330 0.3279 0.3376 0.3324 0.3296 0.3394 0.3305 0.3341 0.3217 0.3255 0.3343 0.3281 0.3333 0.3269 0.3369 0.3353 0.3338 0.3323 0.3330 0.3441 0.3266 0.3196 0.3245 0.3268 0.3260 0.3317 0.3291 0.3315 0.3253

0.0027 0.0025 0.0021 0.0021 0.0024 0.0023 0.0023 0.0021 0.0020 0.0023 0.0027 0.0025 0.0030 0.0027 0.0023 0.0020 0.0023 0.0024 0.0027 0.0023 0.0027 0.0023 0.0024 0.0023 0.0024 0.0022 0.0025 0.0022 0.0022 0.0023

1874 1894 1924 1865 1891 1872 1917 1909 1920 1965 1907 1928 1939 1924 1898 1922 1869 1880 1874 1910 1918 1895 1932 1877 1924 1936 1918 1961 1955 1943

39.0 35.7 33.3 28.9 32.9 36.0 31.5 29.6 25.9 31.5 35.0 32.4 35.2 36.6 35.3 28.4 29.9 36.0 43.5 33.0 33.3 33.2 30.4 39.8 37.8 31.5 31.3 29.6 27.6 31.2

1883 1872 1875 1874 1873 1856 1903 1877 1891 1879 1861 1895 1884 1889 1861 1896 1872 1873 1866 1884 1916 1858 1858 1844 1872 1877 1883 1896 1901 1878

18.6 17.0 15.9 13.6 15.3 17.2 14.8 14.1 12.5 14.9 17.1 18.0 17.4 16.6 16.6 13.2 14.0 17.1 18.3 15.4 16.0 15.1 15.3 16.9 15.8 15.4 15.0 13.8 13.5 14.4

1892 1853 1828 1875 1850 1836 1884 1841 1858 1798 1817 1859 1829 1854 1823 1872 1864 1857 1849 1853 1906 1822 1788 1811 1823 1819 1846 1834 1846 1815

13.0 12.3 10.3 10.2 11.5 11.2 11.1 10.4 9.8 11.4 13.2 12.0 14.4 12.9 11.1 9.8 10.9 11.4 13.1 11.4 13.1 11.3 11.9 11.4 11.7 10.9 12.0 10.6 10.7 11.1

99 98 97 99 98 98 98 98 98 95 97 98 97 98 97 98 99 99 99 98 99 98 96 98 97 96 98 96 97 96

Table 5

Table 6 La Ce Pr Nd analyses for the bright gray domains 1 99269 239869 29324 115655 2 103828 239976 28770 114288 3 93375 229318 28369 112228 4 93194 226580 27649 112929 5 98134 229777 28454 111557 6 94157 221656 26769 108493 7 98549 236928 28382 113953 8 97356 232953 29725 111719 9 95833 230910 28634 114183 10 96722 229277 28145 112805 11 100217 237122 29647 115300 12 100422 241325 28710 111375 13 103929 246959 29487 114138 analyses for the dark domains 1 98477 228499 27961 109232 2 99949 223493 27001 104740 3 100444 223089 26739 97739 4 101139 223272 26526 99752 5 105376 229837 27547 105499 6 99117 229797 27195 104960 7 108426 226156 26624 102933 8 97423 231690 27559 105419 9 105181 227457 26002 102582 10 97778 220774 25740 97729 11 89863 220605 26084 103249 12 101902 230770 27359 105849 13 102353 229662 27673 108144 14 105703 228852 26348 101250 15 102194 232096 27704 107419 16 97504 222727 26508 105512 17 98395 217058 25940 101963 18 105145 230638 26392 105134 19 101222 228684 26464 105461 20 100576 226144 26168 104073

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm Yb

Lu

Y

Th

19841 19586 19854 20960 21120 19914 21619 20655 19736 20406 20217 20086 19971

50.4 54.3 53.3 60.5 81.9 56.3 65.4 53.2 52.5 59.0 50.5 55.3 50.7

9683 9685 9988 11035 11239 9793 10877 10099 9701 10193 9995 9558 9637

641 641 673 740 769 677 742 695 669 706 667 656 657

1590 1607 1678 1808 1901 1594 1831 1770 1626 1766 1632 1591 1646

134 131 142 143 150 129 143 146 135 144 129 134 130

127 126 141 139 141 124 133 139 129 137 131 123 131

6.46 6.53 6.66 6.89 7.01 5.80 6.07 6.97 6.21 7.52 6.12 5.85 6.18

15.8 16.6 15.8 17.5 18.5 15.2 15.4 17.9 15.3 16.7 16.0 16.4 15.1

1.17 0.98 1.07 1.09 1.19 1.01 1.12 1.23 1.14 1.03 0.92 1.15 0.95

3028 3007 3209 3364 3527 3077 3419 3255 3115 3442 3091 3016 3048

73572 68581 81849 80036 58474 75200 60078 68929 72321 74099 66934 66675 72210

21231 19270 19090 19293 19321 19194 19439 20383 19753 18158 17791 20453 20991 18314 19262 19533 20328 19276 19580 19284

101 139 216 242 208 163 493 177 327 198 446 101 215 256 96.4 154 204 210 191 242

11491 11163 11213 11598 11765 11078 13916 12477 13913 10430 9676 12085 12992 10458 10238 12328 12917 11079 11403 11400

959 1074 1114 1125 1274 994 1568 1196 1430 979 898 983 1038 1039 756 1241 1265 1141 1145 1281

3358 4714 5122 4747 6517 4001 6050 4174 5215 4699 3935 3099 3078 4464 2415 4382 5222 5178 5255 6352

419 716 774 732 1013 561 665 451 612 780 581 329 306 643 289 508 730 833 916 957

613 1272 1379 1520 1840 1065 850 642 922 1674 1107 464 410 1216 477 682 1198 1529 1830 1559

39.1 97.3 119 160 145 95.5 47.5 45.5 64.5 171 100 36.0 30.6 113 45.1 48.1 90.0 134 174 124

124 340 445 729 499 373 125 174 194 777 416 132 121 481 185 144 312 489 726 432

8.80 28.0 39.5 71.6 40.7 34.5 8.16 16.7 16.3 73.5 36.9 12.2 10.7 43.4 17.0 11.5 26.9 43.0 66.4 37.0

9935 18303 18415 18282 24669 14258 17095 10973 15308 19281 13911 7707 7750 15227 6970 12142 17463 19416 21434 21812

54010 55577 47496 53260 44097 58851 33212 56226 32978 54246 65678 55454 49747 47195 63797 55729 51606 45796 51110 51367

Highlights First P–T–t path for basement beneath the Yinchan Basin, Western NCC.

1.96 Ga prograde monazite with high Th and low Y and HREE survived later anatexis.

Synchronous formation of metamorphic zircon and retrograde monazite at c. 1.89 Ga.

The Paleoproterozoic basement underwent a prolonged period (c. 70 Ma) of anatexis.