Fluids in deeply subducted continental crust: Petrology, mineral chemistry and fluid inclusion of UHP metamorphic veins from the Sulu orogen, eastern China

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Geochimica et Cosmochimica Acta 72 (2008) 3200–3228 www.elsevier.com/locate/gca

Fluids in deeply subducted continental crust: Petrology, mineral chemistry and fluid inclusion of UHP metamorphic veins from the Sulu orogen, eastern China Ze-Ming Zhang a,*, Kun Shen b, Wei-Dong Sun c, Yong-Sheng Liu d, J.G. Liou e, Cao Shi a, Jin-Li Wang a a

Institute of Geology, Chinese Academy of Geological Sciences, No. 26 Baiwangzhuang Road, Beijing 100037, PR China b Institute of Geological Sciences of Shandong, Lishan Road, Jinan 250013, PR China c Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, PR China d State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, PR China e Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA Received 7 March 2007; accepted in revised form 15 April 2008; available online 24 April 2008

Abstract The complex vein associations hosted in southern Sulu ultrahigh-pressure (UHP) eclogites contain quartz ± omphacite (or jadeite) ± kyanite ± allanite ± zoisite ± rutile ± garnet. These minerals have chemical compositions similar to those of host eclogites. Inclusions of polycrystalline quartz pseudomorphs after coesite were identified in vein allanite and garnet, and coesite inclusions were found in vein zircon. These facts suggest that the veins together with host eclogites have been subjected to synchronous UHP metamorphism. The vein minerals contain relatively high concentrations of rare earth elements (REE), highfield-strength elements (HFSE) and transition metal elements (TME). A kyanite–quartz vein has a whole-rock composition similar to adjacent UHP metamorphic granitic gneisses. Abundant primary multi-solid fluid inclusions trapped within UHP vein minerals contain complex daughter minerals of muscovite, calcite, anhydrite, magnetite, pyrite, apatite, celestite and liquid and gas phase of H2O with solids up to 30–70% of the inclusion volume. The presence of daughter minerals anhydrite and magnetite indicates the subduction fluids were oxidizing, and provides a possible interpretation for the high oxygen fugacity of subduction zone magmas. These characteristics imply that the UHP vein minerals were crystallized from supercritical silicate-rich aqueous fluids that were in equilibrium with peak-UHP minerals, and that the fluids in deeply subducted continental crust may contain very high concentrations of silicate as well as HREE, HFSE and TME. Such fluids might have resulted in major fractionation between Nb and Ta, i.e. the UHP fluids have subchondritic Nb/Ta values, whereas the host eclogites after extraction of the fluids have suprachondritic Nb/Ta values. Therefore, voluminous residual eclogites with high Nb/Ta ratios may be the complementary suprachondritic reservoir capable of balancing the subchondritic depleted mantle and continental crust reservoirs. Ó 2008 Elsevier Ltd. All rights reserved.

1. INTRODUCTION The segments of subduction zones extending from trenches to beneath volcanic arcs are sites of profound chemical changes (Hermann, 2002a; Manning, 2004). *

Corresponding author. Fax: +86 10 68999735. E-mail addresses: [email protected], [email protected] (Z.-M. Zhang). 0016-7037/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.gca.2008.04.014

The subducting slabs transport large amount of fluids containing both major and trace elements upward into the overlying mantle wedge and ultimately induces partial melting. The chemical processes in this ‘‘subduction factory” are fundamental to the Earth’s evolution because they lead to prolific volcanism and degassing, mediation of the global cycling of elements and over time production of the continental crust (Manning, 2004).

Fluids in deeply subducted continent

Recent high-pressure (HP) experiments and petrologic studies of eclogite-facies rocks demonstrate that numerous hydrous phases transport fluid into the mantle wedge, which subsequently incorporate into arc magmas and the deep mantle along the subduction zone (e.g., Maruyama and Liou, 1998; Hermann and Green, 2001; Hermann, 2002a,b; Tsujimori et al., 2006). In eclogite-facies rocks, the presence of large ion lithophile elements (LILE) and light rare earth elements (LREE) in hydrous phases, such as lawsonite and epidote-group minerals, together with high-field-strength elements (HFSE) repositories, such as rutile and other Ti-rich minerals, control the trace element budget of evolved fluids and fluid-mediated cycling of slab components into the overlying mantle (Hermann and Green, 2001; Scambelluri and Philippot, 2001; Hermann, 2002a; Manning, 2004). Relevant investigations have shown that many DabieSulu eclogitic rocks contain hydrous minerals and carbonates (epidote, zoisite, phengite, magnesite, dolomite, talc, clinohumite, etc.) (Zhang et al., 1994, 1995, 2000a; Liou et al., 1995, 2000; Yang and Jahn, 2000; Yang, 2003; Zhang et al., 2000b, 2003), primary fluid inclusions in matrix minerals (e.g., Shen et al., 1996; You et al., 1996; Xiao et al., 2000, 2001; Fu et al., 2001, 2003; Zhang et al., 2005a, 2006d; Ferrando et al., 2005a,b), as well as metamorphic veins (Castelli et al., 1998; Franz et al., 2001). These hydrous minerals, fluid inclusions and veins were formed at HP–UHP conditions, at pressures up to the stability fields of coesite and diamond. These characteristics provide a unique opportunity to constrain fluid–rock interactions during continental subduction and collision. Nevertheless, we still lack basic information on the compositions of fluids released from subducting slabs and its controlling factors. No direct, pristine fluid sample can be collected from the subduction environment. In addition, experimental study of fluids at the requisite high pressures and temperatures has proven to be a sin-

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gular challenge (Manning, 2004). As a result, fundamental questions remain: are fluids in subducting zone dilute solutions or silicate-rich mixtures intermediate between H2O and melt? How does mineral solubility and element partitioning change along the flow path? Answering these questions requires a better understanding of the chemical behavior of the fluid phase at greater depths (Manning, 2004). In this paper, we describe some complex UHP veins which are rich in hydrous phases (allanite, zoisite and epidote), and also contain significant amounts of rutile. These veins are hosted in UHP eclogites from the southern Sulu area and have not been described in previous studies of Dabie-Sulu UHP rocks. The petrology, mineral chemistry, and fluid inclusion data are combined to (1) constrain the composition of fluids generated in rocks that have been subducted to depths of more than 100 km, (2) evaluate the effect of fluid–melt interactions on element mobility at depths relevant to partial melting of the overlying mantle wedge, and (3) examine the major Nb and Ta fractionation in the released supercritical fluids and the residual UHP eclogite. 2. GEOLOGICAL SETTING AND SAMPLES The Dabie-Sulu orogen between the North China and the Yangtze Plates contain abundant coesite-bearing UHP metamorphic rocks (e.g., Xu et al., 1992; Liou et al., 1995; You et al., 1996; Cong and Wang, 1996; Wallis et al., 1999). The present study focuses on the Donghai area in southern Sulu (Fig. 1), which contains a variety of UHP rocks (Hirajima et al., 1990, 2003; Enami et al., 1993; Zhang et al., 1994, 1995, 2000a; Yang and Jahn, 2000; Zhang et al., 2000b, 2005c). Numerous investigations have yielded several important conclusions: (1) P–T conditions of UHP metamorphism are 3.0–4.5 GPa and 700–850 °C. The retrograde P–T paths are characterized by isothermal decompression or by decompression with only a slight

Zhimafang

Q

fault

W

lt

Tan-L u

be

Yellow Sea

HP

be l JX t F

Fig.1 Donghai

Qingdao

P

Qinglongshan

North China Plate

UH

Donghai

YF

Weihai

Chizhuang

CCSD

5 Km

Yangtze Plate

120km

Gneiss and foliation

Maobei Eclogite or peridotite

Quaternary Tertiary

CCSD

Drill site of CCSD

Fig. 1. Simplified geological map of Donghai area showing the locations of the Chizhuang and other eclogite bodies.

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temperature decrease (Hirajima et al., 1990; Enami et al., 1993; Zhang et al., 1994, 1995, 2000a,b, 2005d, 2006c). (2) Inclusions of coesite occur in zircons from both eclogites and country rocks, including gneisses, quartzite and marble, suggesting in-situ UHP metamorphism and deep subduction of entire block of continental crust (Tabata et al., 1998; Ye et al., 2000; Liu et al., 2001a,b). (3) UHP minerals from both eclogite and gneiss have unusual negative d18O values, indicating that their protoliths had interacted with strongly 18O-depleted meteoric water before subduction (e.g., Yui et al., 1995; Zheng et al., 1996, 2003; Rumble and Yui, 1998; Rumble et al., 2002; Zhang et al., 2005a, 2006c; Xiao et al., 2006b); (4) country rocks together with eclogites have been subjected to synchronous UHP metamorphism (Zhang et al., 1994, 1995, 2000a; Zhang et al., 2000b, 2003, 2006c; Liu et al., 2001a,b, 2003). (5) The rocks were metamorphosed at UHP conditions at 230–240 Ma and retrograded to quartz–eclogite-facies conditions at 220 Ma (e.g., Li et al., 1993; Zheng et al., 2003; Zhao et al., 2006). (6) The protoliths of UHP rocks are bimodal volcanic rocks, which were formed in a continental rift at about 700–800 Ma (e.g., Zheng et al., 2003; Zhang et al., 2006b). (7) Fluids of variable amounts and compositions attended UHP metamorphism, but the fluid flows were believed to be very limited (e.g., Xiao et al., 2000, 2001, 2006b; Fu et al., 2003; Shen et al., 2003a,b; Zheng et al., 2003; Ferrando et al., 2005a,b; Zhang et al., 2005b, 2006a,d). Regional geological mapping, the shallow holes, and the Chinese Continental Scientific Drilling Project (CCSD) drill cores have revealed some large eclogitic bodies, including those in Maobei, Chizhuang, Zhimafang and Qinglongshan as well as numerous small eclogite lenses; these mafic eclogites together with minor garnet peridotite make up a large mafic to ultramafic UHP belt of 40 km in length and 10 to 15 km in width in the southern Sulu area (Fig. 1). The country-rocks surrounding these eclogites and garnetperidotites are granitic gneisses with minor marbles and pelitic schists. The eclogitic rocks of this study, hereafter referred to as the Chizhuang eclogite, were sampled in a quarry of about 10 m long, 10 m wide and 1–3 m deep at Chizhuang village, Donghai county, about 2.5 km to the northwest of the drill site of the CCSD. The quarry cannot be completely mapped and sampled because it has been partly filled by rain water and mud. Various types of veins and eclogites accessible from outcrop were collected, and other typical samples were taken from large, quarried eclogite blocks that could not otherwise be found in the limited surface area of the outcrop. Most eclogites are foliated, as defined by the alignment of elongated omphacite prisms, phengite flakes and zoisite plates, alternating garnet-enriched and omphacite-enriched bands. Usually this primary foliation has also been folded (Fig. 2). Veins parallel to or cross-cutting the eclogitic foliation at a low angle distribute as lenses or thin layers of a few centimeters to tens of centimeters wide and several tens of centimeters to several meters long in the Chizhuang eclogite (Fig. 2). In addition to quartz, these veins contain variable amount of allanite, zoisite, omphacite, kyanite, rutile, garnet, apa-

tite and zircon. The veins are unevenly distributed and account for about 2–5 vol% of the whole eclogite body as estimated both from the outcrop surface and from the rock blocks. Cross-cutting relationships among individual veins were not observed in this quarry. To investigate a possible compositional exchange between the veins and the host eclogite, samples were collected at intervals of several centimeters across the vein–eclogite contact. Eclogite samples CZ18E-1 and CZ18E-2 were obtained at distances of 5 and 10 cm, respectively, from the allanite– quartz vein sample CZ18V. Eclogite sample CZ7E was obtained at a distance of 20 cm from an omphacite–quartz vein; other samples, such as CZ1E and CZ14E, were obtained at distances of more than 30–50 cm from veins. The first three samples are referred to as eclogites adjacent to veins, whereas the other samples as eclogites away from the vein (also see below). 3. ANALYTICAL METHODS For bulk rock analysis, 500 g of each sample was crushed to 60 mesh in a steel jaw crusher; and then about 60 g of each crushed sample was powdered in an agate ring mill to less than 200 mesh. All the samples were analyzed in the National Geological Analysis Center of China, Beijing. Major elements were determined by XRF (Rigaku-3080) and the analytical uncertainty is <0.5%. FeO contents were determined by the wet chemical analysis method. Trace elements Zr, Nb, V, Cr, Sr, Ba, Zn, Ni, Rb and Y were determined using a XRF instrument (Rigaku-2100), and the analytical uncertainties are <5% for Ba and <3% for all other elements. Other trace elements were analyzed by ICP-MS (TJA-PQ-ExCell) with the analytical uncertainties of 1–5% at abundances >1 ppm, and 5–10% at abundances <1 ppm. Major and trace element abundances of minerals were determined at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences. Major elements were determined by electronmicroprobe analysis using a JXA-8900RL Jeol Superprobe equipped with a WDS/EDS combined micro-analyzer. Analyses were performed on polished sections at 15 kV accelerating voltage, 12 nA beam current, and about 5 lm probe diameter. Standards used include silicates and pure oxides. In-situ trace element analyses were performed by laser-ablation LA-ICP-MS (GeoLas 2005) equipped with a 193 nm ArF-excimer laser (COMPEXPro). Helium was used as carrier gas to enhance the transport efficiency of the ablated material. During experiments, the output energy was set to 80 mJ, with a pulse repetition rate of 8 Hz and laser spot of 32 lm in diameter. The ICP-MS system is an Agilent 7500a equipped with a shield torch. Calcium (43Ca) was used as an internal standard and NIST610 as an external standard. Factory-supplied time resolved software was utilized for the acquisition of each individual analysis. The time-resolved spectra were processed off line using Glitter (ver4.0, Macquarie University) to calculate the contents of trace elements. Results obtained on international standard materials BCR-2G and BHVO-2G show that accuracy is better than 5%.

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Fig. 2. Photographs of the Chizhuang UHP eclogites and veins. (A) Eclogite exhibits distinct foliation defined by the alignment of elongated omphacite prisms, as well as garnet-enriched and omphacite-enriched bands, and a distinct fold structure. The omphacite–quartz veins occur as lenses in the fold hinge and as thin layers parallel to the eclogitic foliation and banding. Note that some omphacite grains have been replaced by light green or offwhite symplectite of amphibole plus plagioclase; (B) quartz veins with variable amounts of omphacite occurring as thin layers parallel to the eclogitic foliation, or as dendritic cross-cutting the foliations at a low angle; (C) omphacite–kyanite–quartz vein occurring parallel to the foliation in eclogite; (D) quartz vein with a long prismatic omphacite megacryst occurring as dendritic nearly parallel to the eclogitic foliation. The vein omphacite was partly replaced by the light green symplectite of amphibole and plagioclase; (E) dendritic quartz vein with rare rutile occurring nearly parallel to the eclogitic foliation; (F) dendritic omphacite–quartz veins paralleling or cross-cutting the eclogitic foliation at a low angle. The coin in all photographs is 2.5 cm in diameter.

4. PETROGRAPHY The mineral abbreviations used in the petrographic descriptions below are from Kretz (1983). All Chizhuang eclogites contain similar minerals, including garnet (Grt), omphacite (Omp), phengite (Phn), kyanite (Ky), zoisite (Zo), quartz (Qtz), rutile (Rt), apatite (Ap) and zircon (Zrn) (Table 1). The eclogites adjacent to quartz veins, such as samples CZ18E-1, CZ18E-2 and CZ7E, have relatively high abundances of quartz in addition to zoisite, and therefore have higher SiO2 content (see following sections). Some eclogites and veins have been subjected to variable

degrees of amphibolite-facies retrograde metamorphism, i.e. omphacite is replaced by a symplectitic corona of amphibole + albite, garnet by amphibole ± plagioclase, phengite by biotite + plagioclase, and rutile by ilmenite ± titanite. Rarely, inclusions of polycrystalline quartz pseudomorphs after coesite are recognized in garnet and omphacite in both fresh and retrograded eclogites. Laser Raman spectroscopic analyses show that eclogitic zircons contain coesite and other mineral inclusions of eclogite-facies. These and previous results have demonstrated that all eclogites and their gneissic country rocks from the southern Sulu area have experienced synchronously in-situ UHP

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Table 1 Mineral assemblage and content of the analyzed eclogite and vein samples Sample

Rock

Minerals and their volume content (%)

CZ1E

Eclogite

CZ7E

Eclogite

CZ14E

Eclogite

CZ18E-1

Eclogite

CZ18E-2

Eclogite

CZ19E

Eclogite

CZ25E

Eclogite

Grt 35, Omp 43, Zo10, Ky 5, Qtz 5, Rt 2 Grt 30, Omp 35, Zo 15, Ky 5, Phn 8, Qtz 5, Rt 2 Grt 35, Omp 45, Zo 15, Qtz 3, Rt 2 Grt 35, Omp 40, Zo15, Qtz 7, Rt 3 Grt 35, Omp 45, Zo 10, Qtz 8, Rt 2 Grt 35, Omp 40, Ky 8, Zo10, Qtz 5, Rt 2 Grt 45, Omp 45, Qtz 7, Rt 3

CZ18V

Aln–Qtz vein

CZ20V

Aln–Qtz vein

CZ2V

Omp–Qtz vein

CZ3V CZ6V CZ4V CZ26V CZ9V-1

Omp–Qtz vein Omp–Qtz vein Zo–Qtz vein Zo–Qtz vein Ky–Qtz vein

CZ9V-2

Ky–Qtz vein

CZ25V

Qtz vein

Aln 10, Omp 20, Ky 10, Qtz 55, Rt 5 Aln (Zo) 10, Omp 15, Ky 15 Qtz 50, Ap 5, Rt 5 Omp 15, Ky 10, Ap 5, Qtz 74, Rt 1 Omp 40, Zo 15, Qtz 30, Rt 15 Omp 70, Qtz 28, Rt 2 Zo 20, Ky 10, Qtz 65, Rt 5 Zo 60, Qtz 40 Grt 8, Jd 20, Ky 15, Zo 20, Qtz 35, Rt 2 Grt 7, Jd 20, Ky 16, Zo 18, Qtz 37, Rt 2 Qtz 98, Rt 2

metamorphism (e.g., Zhang et al., 1995, 2000b, 2003; Liu et al., 2001a,b). The veins in Chizhuang eclogites have different mineral assemblages and variable modal contents. Moreover, distribution of minerals is inhomogeneous even in a single vein (Fig. 2). Therefore, it is difficult to estimate accurately the mineral contents of veins. Roughly, these veins are divided into five groups: allanite–quartz, omphacite– quartz, zoisite–quartz, kyanite–quartz and quartz veins (Table 1).

Allanite–quartz veins usually have a mineral association of allanite (Aln) + omphacite + kyanite + rutile + quartz + zircon ± apatite. As shown in Fig. 3A and B, vein minerals have distinctly larger grain sizes compared to minerals in the host eclogite. These large crystals of allanite, omphacite, rutile and kyanite occur as aligned prisms of 0.5–4 cm long and 0.1–0.5 cm wide associated with fine-grained (about 0.5–2 mm in size) minerals of quartz, kyanite, omphacite, rutile and apatite. Garnet occurs only in host eclogite whereas allanite is present only in veins. Similar to the host eclogite, omphacite grains in veins also show slight retrogression, and are replaced by a thin corona of needle-like amphibole + albite symplectite. A large allanite grain in sample CZ20V has an irregular thin zoisite rim, and therefore shows pronounced optical zoning with a brown inner zone surrounded by a colorless rim (Fig. 3B). Some allanite crystals contain inclusions of polycrystalline quartz pseudomorphs after coesite, and exhibit radial fractures. In addition, coesite also occurs as inclusions in zircon from allanite–quartz veins. It has been noted that cores of large allanite crystals contain abundant multiphase fluid inclusions and are surrounded by inclusion-free outer rims (also see following description). Omphacite–quartz veins contain variable amounts of kyanite, zoisite, apatite, and rutile in addition to quartz and omphacite (Table 1 and Fig. 2). Abundant rutile and zoisite in sample CZ3V occur as large subhedral megacrysts, whereas omphacite occurs mainly as smaller grains, and has been partly replaced by amphibole + albite symplectite (Fig. 3C). Zoisite–quartz veins contain euhedral platy zoisite crystals up to 5–20 cm in width and quartz crystals of 2–5 mm in size (Fig. 3D), with or without minor kyanite and rutile. Rarely, zoisite occurs as needles in quartz grains. Kyanite–quartz veins consist mainly of kyanite, quartz, allanite (or epidote) and jadeite with minor garnet, phengite and rutile and trace amount of zircon (Fig. 3E). Most kyanite grains are rimed with retrograde minerals consisting of plagioclase and/or paragonite. Almost all jadeite grains have been transformed into amphibole + albite symplectite. Most epidote-group minerals show clear growth zoning with a large allanite core and a narrow epidote rim. Minor vein garnet grains occur as euhedral crystals and contain inclusions of polycrystalline

" Fig. 3. Photographs of the UHP veins. (A) Allanite–quartz vein and hosted eclogite (sample CZ18V). The vein consists of aligned long prismatic allanite, omphacite, rutile and kyanite megacrysts, and relatively fine-grained quartz crystals. Note that the core of the light brown allanite megacryst contains very fine-grained and dense needle fluid inclusions parallel to the c-axis of the host mineral. Omphacites from the vein and host eclogite are partly replaced by the symplectitic corona of needle amphibole + plagioclase with dark color. The red dashed curve is a rough boundary between the vein and host eclogite; (B) allanite–quartz vein and hosted eclogite (CZ20V). The vein consists of largegrained allanite, omphacite and rutile megacrysts, and fine-grained quartz, kyanite, omphacite and apatite. The long, brown, prismatic allanite crystal contains omphacite and quartz inclusions as well as very fine-grained and dense fluid inclusions parallel to the c-axis of the host mineral, and has an incomplete and narrow rim of colorless, inclusion-free zoisite. Omphacite from the vein and host eclogite is rimmed by a symplectitic corona of needle amphibole + plagioclase. The red, dashed curve is a rough boundary between the vein and host eclogite, and the thin, yellow, dashed line crossing the allanite megacryst is the location of the analyzed compositional profile shown in Fig. 6; (C) omphacite– quartz vein (CZ03V) containing abundant rutile and zoisite. Omphacite grains are partly replaced by amphibole + plagioclase symplectite; (D) zoisite–quartz vein (CZ24V). The zoisite grains are more than 10–20 cm in size, and the quartz grains are up to 0.5–1 cm in size. The scale coin is 2.5 cm in diameter; (E) kyanite–quartz vein (CZ9V) consisting of kyanite, quartz, garnet and retrogression minerals. The jadeite is completely replaced by the symplectite (Sym) of needle amphibole and plagioclase, and kyanite is rimmed by a corona of paragonite and/or plagioclase. Note that the garnet contains inclusions of polycrystalline quartz pseudomorph after coesite, and shows radial fractures around the inclusion. The images are taken with a microscope under plain light, except for (D) from the specimen.

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quartz pseudomorph after coesite (Fig. 3E). Zircon from kyanite–quartz veins contains coesite, garnet and jadeite inclusions. These quartz veins are composed predominantly of quartz, with or without trace kyanite, omphacite, zoisite, apatite and rutile (Fig. 2E). Parageneses and textures of vein minerals in UHP eclogites mentioned above yield several conclusions: (1) these veins contain abundant Si- and Al-rich minerals, such as quartz, kyanite, allanite, zoisite and epidote; (2) most vein minerals form very large euhedral to subhedral crystals (or megacrysts), indicating that they were crystallized freely from silicate-rich fluids or melts; (3) most vein minerals with the exception allanite also occur in host eclogite; some vein minerals contain inclusions of coesite or polycrystalline quartz pseudomorph after coesite, indicating that these veins formed during UHP metamorphism, hence may originally have been coesite- rather than quartz-rich veins; (4) all these veins contain a large amount of allanite, zoisite, rutile, and minor apatite, which are repositories of LILE, LREE, and HFSE in meta-mafic rocks; (5) many vein minerals contain abundant primary fluid inclusions with multiple solids, indicating that these veins were crystallized from silicate-rich aqueous fluids or melts. 5. PETROCHEMISTRY Seven samples including five eclogites and two kyanite– quartz veins were analyzed for major and trace elements. The results are listed in Table 2. The whole-rock compositions of most veins cannot be obtained due to the very large size of mineral grains and heterogeneous mineral distribution. Overall, eclogites adjacent to the veins, such as samples CZ18E-1, CZ18E-2 and CZ7E contain higher SiO2, TiO2 and V, and lower Al2O3, MgO, CaO, Sr, Cr and Ni contents than other eclogites away from the veins. Moreover, sample CZ18E-1 and CZ18E-2 have high REE concentrations with REE patterns showing highly enriched LREE, flat HREE and slightly depleted MREE (Fig. 4A). In contrast, eclogites away from veins have SiO2 content similar to or slightly lower than that of typical mafic rocks, relatively high Sr, Cr and Ni contents and low REE concentrations. Their REE patterns are characterized by enriched LREE and depleted HREE, with distinct positive Eu anomalies (Fig. 4A). In comparison to the primitive mantle, they are enriched in some LILEs, such as Rb, Ba, K and Sr, depleted in Nb, Ta and Ti. These characteristics are similar to the Al-rich eclogite from the adjacent Maobei body, which has been demonstrated to be a plagioclase- and clinopyroxene-enriched cumulate layered gabbro intrusion formed by fractional crystallization of a basaltic magma in a continental environment (Zhang et al., 2006b,c). Kyanite–quartz veins have relatively high SiO2 contents of up to 78.7 wt% (Table 1), and chemical compositions comparable to those of granitic gneisses with similar SiO2 content from the CCSD main drill hole (Zhang et al., 2006b,c). Moreover, these veins and granitic gneisses have similar REE patterns, with an enriched LREE, flat HREE and especially pronounced negative Eu anomalies (Fig. 4A). They also show similar negative

Sr, Nb, Ta and Ti anomalies compared to the primitive mantle. However, these veins have higher Al2O3, CaO and Th, and lower Na2O, K2O, Rb and Ba contents than the gneisses. Therefore, we suggest that these veins were probably derived from a granitic melt formed by partial melting during the UHP metamorphism (also see following sections). 6. MINERAL CHEMISTRY All minerals present as primary UHP phases in the investigated samples were analyzed. Representative mineral compositions are listed in Tables 3–13. The trace element concentrations of several eclogitic rutile and apatite grains with size of <30 lm, such as those in CZ7E, CZ18E-1, CZ18E-2 and CZ25E, were not obtained by in-situ LAICP-MS method due to analytical difficult. 6.1. Garnet Garnets in the eclogite and vein samples show large compositional variations; their pyrope, almandine and grossular components vary in ranges of 17.7–37.8%, 23.1– 47.1% and 27.3–40.6%, respectively (Table 3). Garnet in Ky–Qtz veins has higher almandine, grossular, but lower pyrope contents than those from eclogites. For trace elements, garnet has relatively high Zn (50–216 ppm), Co (50–149 ppm), Sc (21–82 ppm) and Y (9–200 ppm) concentrations with minor V, Cr, Ni and Ga compared to other minerals (Table 4). Abundances of other trace elements, such as Nb, Ta, Hf, Pb, Th, U and Cs, are close to or below the detection limits. All garnet grains analyzed, especially those from Ky–Qtz veins, have HREE concentrations higher than their host rocks, with LREE depletion and HREE enrichment in chondrite normalized diagrams (Figs. 4B and 5). 6.2. Omphacite Clinopyroxenes from both eclogites and veins are omphacitic, with jadeite components ranging from 35.4% to 62.6% (Table 5). Overall, omphacite grains analyzed from veins exhibit characteristics similar to those from eclogites in terms of major and trace elements. Among all UHP minerals, omphacite has the highest Ni (61– 430 ppm) concentrations and significant amounts of V, Zn, Cr, Sr, Co, Cu and Ga (Table 6), with relatively low REE concentrations and REE patterns showing enrichment in MREE and depletion in LREE and HREE (Figs. 4C and 5). REE concentrations of some omphacite grains are below the detection limits. No detectable major and trace element zonation was found in omphacite grains, including the omphacite megacrysts in veins. 6.3. Epidote-group minerals Allanite can incorporate several weight percents of LREE, e.g., La, Ce and Nd, as well as Th (for more information, see Giere and Sorensen, 2004). Allanite from Chizhuang UHP veins has total REE concentrations of 5.4–

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Table 2 Whole-rock compositions of the eclogites and kyanite–quartz veins Sample: Rock: SiO2 (wt%) TiO2 Al2O3 FeO Fe2O3 MnO MgO CaO Na2O K2O P2O5 H2O CO2 Total Sr (ppm) Zr Ba V Zn Cr Co Ni Cu Ga Rb Nb Ta Hf Pb Th U Sc Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

CZ1E Eclogite

CZ7E Eclogite

CZ14E Eclogite

45.79 0.31 23.30 3.79 2.16 0.13 6.76 14.94 1.97 0.13 0.03 0.40 0.09 99.80

53.58 0.38 22.61 3.71 1.98 0.10 4.17 8.06 3.82 0.73 0.07 0.42 0.09 99.72

46.08 0.32 26.24 3.02 2.22 0.10 5.63 13.70 1.68 0.20 0.06 0.46 0.14 99.85

61.01 1.25 19.22 4.87 1.52 0.11 2.96 6.81 1.90 0.04 0.06 0.02 0.10 99.87

65.09 1.10 16.44 4.36 1.44 0.11 2.54 6.60 1.79 0.03 0.29 0.02 0.09 99.90

78.06 0.21 13.41 1.10 0.64 0.03 1.03 2.78 1.75 0.26 0.02 0.44 0.04 99.77

78.74 0.23 13.36 1.11 0.70 0.03 1.02 2.80 1.70 0.26 0.01 0.48 0.04 100.48

522.00 25.20 27.80 75.00 36.00 371.58 36.50 111.00 16.00 13.00 4.43 0.44 0.05 0.50 8.97 0.53 0.21 35.50 5.90

198.00 13.80 164.00 134.00 58.00 41.98 24.30 38.20 28.00 23.00 17.40 0.25 0.05 0.34 15.80 0.14 0.06 9.33 2.75

606.00 18.50 33.70 77.00 26.00 197.58 30.70 78.90 7.00 14.00 6.38 0.23 0.05 0.41 8.19 0.44 0.16 24.90 5.90

145.00 382.00 13.30 144.00 46.00 39.48 21.40 23.00 15.00 18.00 1.30 1.49 0.16 8.15 6.59 7.64 1.79 18.10 25.30

268.00 312.00 16.90 135.00 46.00 10.58 18.50 18.50 19.00 18.00 1.11 2.66 0.23 7.46 6.25 6.85 1.70 17.00 27.90

393.00 124.00 50.80 43.00 23.00 6.58 4.53 9.65 30.00 14.00 5.11 2.16 0.20 4.21 7.11 8.79 1.54 5.34 12.00

397.00 132.00 51.00 42.00 24.00 6.78 4.51 9.52 30.00 14.00 5.05 2.54 0.23 3.78 7.06 9.19 1.58 5.24 11.30

3.90 6.85 0.94 4.26 0.85 0.43 0.88 0.14 0.88 0.19 0.55 0.08 0.50 0.08

5.76 11.80 1.61 7.36 1.20 0.75 0.94 0.11 0.50 0.10 0.31 0.05 0.31 0.05

4.96 9.68 1.29 6.00 1.08 0.54 1.05 0.17 0.98 0.19 0.60 0.09 0.53 0.09

67.90 135.00 16.50 67.70 8.48 2.22 6.26 0.73 3.66 0.85 3.38 0.53 3.75 0.61

65.90 130.00 16.10 67.10 8.97 2.43 6.97 0.82 4.31 0.97 3.59 0.58 4.14 0.68

60.20 115.00 13.80 53.20 7.50 1.52 6.23 0.65 2.46 0.41 1.28 0.16 1.16 0.18

57.90 112.00 13.10 50.10 7.09 1.44 5.78 0.60 2.33 0.39 1.20 0.16 1.11 0.17

7.1 wt%, including 1.3–1.7 wt% of La2O3, 2.5–3.3 wt% of Ce2O3, and 1.1–1.4 wt% of Nd2O3 (Table 7). In addition, allanite has the highest Th (1061–1896 ppm), U (434– 585 ppm) and Pb (108–150 ppm) concentrations among all minerals from eclogites and veins studied here, and also has relatively high Sr (6562–7493 ppm), Ba (31–45 ppm), V (529–639 ppm), Zn (91–119 ppm) and Ga (113–129 ppm) with minor Cr, Zr, Co and Ni concentrations (Table 8). The REE patterns of allanite display strong enrichments in LREE with respect to HREE (Fig. 4D).

CZ18E-1 Eclogite

CZ18E-2 Eclogite

CZ9V-1 Vein

CZ9V-2 Vein

Zoisite from eclogites and veins has a formula close to the ideal one of Ca2Al3Si3O12(OH), with only minor Fe2O3 (1.0–2.7 wt%) (Table 9). The transition from zoisite to allanite is characterized by a continuous decrease in SiO2, CaO and Al2O3, and an increase in total REE, especially LREE. Like allanite, most zoisite grains have relatively high but variable Sr (up to 14,193 ppm), Ba, V, Cr and Pb concentrations (Table 10), and REE concentrations higher than their host rocks, with LREE enrichment and HREE depletion and usually pronounced positive Eu

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Z.-M. Zhang et al. / Geochimica et Cosmochimica Acta 72 (2008) 3200–3228

A, Whole rock

B, Garnet

1000.0

1000.0

100.0

CZ14E

CZ7E

CZ18E-1

CZ9V

CZ18E-2

10.0

Sample/Chondrite

Sample/Chondrite

CZ1E CZ1E

CZ7E

100.0

CZ7E CZ9V

10.0 1.0

CZ9V CZ14E

0.1

CZ19E CZ25E

1.0

0.01

La Ce Pr Nd SmEu GdTb Dy Ho Er TmYb Lu

La Ce Pr Nd SmEu Gd Tb Dy Ho Er TmYb Lu

C, Omphacite

D, Allanite 100000.0

10.0

CZ1E

CZ6V

CZ2V

CZ7E

CZ3V

CZ7E CZ14E

1.0 0.1 0.01 0.001

CZ18V

CZ20V

CZ19E

CZ25E

CZ18V

10000.0

Sample/Chondrite

Sample/Chondrite

100.0

CZ18V CZ18V CZ18V

1000.0 100.0

CZ20V CZ20V

10.0

CZ20V CZ20V

1.0 La CePr Nd SmEu GdTb Dy Ho Er TmYb Lu

La Ce Pr Nd SmEu GdTb Dy Ho Er TmYbLu

E, Zoisite

F, Apatite CZ1E CZ3V CZ4V CZ7E CZ9V

1000.0 100.0 10.0 1.0 0.1

CZ14E CZ14E CZ19E

CZ20V CZ20V CZ26V

La Ce Pr Nd SmEu GdTb Dy Ho Er TmYb Lu

1000.0

Sample/Chondrite

Sample/Chondrite

10000.0

CZ2V CZ20V CZ20V

100.0

CZ20V

10.0

1.0

La Ce Pr Nd SmEu GdTb Dy Ho Er TmYb Lu

Fig. 4. Chondrite-normalized REE patterns of eclogite and kyanite–quartz veins, and UHP minerals from the vein and host eclogite.

anomalies (Figs. 4E and 5). Although zoisite grains from various eclogites and veins show considerable variations in terms of trace elements, no systematic compositional differences are found in zoisite from host eclogites and veins. In contrast to allanite and zoisite, epidote occurring in Ky– Qtz veins has a higher Fe2O3 (5.92–6.32 wt%), much higher Zn (up to 601 ppm) and Cu (up to 109 ppm), and slightly high but variable V, Cr, Co, Ga and Sc concentrations (Tables 9 and 10). The epidote also has very low REE concentrations with flat REE patterns (Table 10 and Fig. 5C). Epidote-group minerals in some veins are zoned crystals in which allanite occurs in the core, and zoisite and/or epidote in the rim (Fig. 3B). As shown in Fig. 6, the compositional variations, especially for REEs between the core and

rim are very clear. Asymmetrical changes for some element contents between the left and right rims of the same zoisite grain were recognized. Vanadium and Ga concentrations of the narrower zoisite rim are the same as those of the allanite core. Moreover, the Y concentrations of the two rims show opposite trends. Apparently allanite is a major sink for all REEs, Cr, Ni, Co, Sc, V, Zn and HFSE as well as Th and U, as suggested by previous investigators (see review by Giere and Sorensen, 2004). 6.4. Rutile Rutile has the highest Zr (up to 185 ppm), V (up to 2695 ppm) and Mo concentrations of all analyzed minerals

Fluids in deeply subducted continent

3209

Table 3 Major element compositions of the garnet from the eclogites and kyanite–quartz veins Sample: Comment: Rock:

CZ1E cz1-5 Eclogite

CZ7E cz7-2 Eclogite

CZ7E cz7-9 Eclogite

SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O K2O Total

38.62 0.05 22.24 0.03 16.30 0.00 7.97 13.18 0.02

39.14 0.00 22.28 0.04 23.70 0.03 6.67 9.95 0.04 0.00 101.84

38.79 0.04 22.33 0.02 22.94 0.03 6.38 10.75 0.03 0.01 101.32

98.41

CZ9V cz09-3-1 Vein

CZ9V cz09-4-4 Vein

CZ14E cz14-7 Eclogite

CZ19E cz19-5 Eclogite

38.57 0.01 22.43

38.69 0.02 21.69

22.10 0.02 6.65 11.11

21.44

39.01 0.06 22.57 0.05 17.13 0.01 9.16 12.25

39.92 0.05 22.74 0.02 13.19 0.01 10.14 14.56

0.02 100.26

0.01 100.64

100.88

4.60 14.63 0.02 0.00 101.10

CZ25E cz25-4 Eclogite 38.21 0.07 22.14 0.02 18.75 7.84 12.51

99.54

CZ25E cz25-5 Eclogite 38.81 0.02 22.47 19.02 0.00 7.78 11.99 0.03 100.13

Si Ti Al Cr Fe3+ Fe2+ Mn Mg Ca Na K Cations

2.955 0.003 2.005 0.002 0.079 0.964 0.000 0.909 1.080 0.003 0.000 8.000

2.955 0.000 1.983 0.002 0.109 1.388 0.002 0.751 0.805 0.006 0.000 8.000

2.943 0.002 1.996 0.001 0.117 1.339 0.002 0.722 0.874 0.004 0.001 8.000

2.930 0.001 2.008 0.000 0.130 1.273 0.001 0.753 0.904 0.000 0.000 8.000

2.955 0.001 1.952 0.000 0.138 1.231 0.000 0.524 1.197 0.003 0.000 8.000

2.921 0.003 1.992 0.003 0.156 0.916 0.001 1.023 0.983 0.000 0.002 8.000

2.943 0.003 1.975 0.001 0.133 0.680 0.001 1.114 1.150 0.000 0.001 8.000

2.908 0.004 1.985 0.001 0.189 1.004 0.000 0.889 1.020 0.000 0.000 8.000

2.937 0.001 2.004 0.000 0.123 1.081 0.000 0.878 0.972 0.004 0.000 8.000

Prp Grs Alm Sps Adr

0.308 0.366 0.326 0.000 0.038

0.255 0.273 0.471 0.001 0.052

0.246 0.298 0.456 0.001 0.055

0.257 0.308 0.434 0.000 0.061

0.177 0.406 0.417 0.000 0.066

0.350 0.336 0.314 0.000 0.073

0.378 0.390 0.231 0.000 0.063

0.305 0.350 0.345 0.000 0.087

0.299 0.332 0.369 0.000 0.058

from veins and eclogites studied here and contains almost all the Nb (mean value = 235.6 ppm) and Ta (mean value = 22.7) of the whole-rock (Table 11). In addition, rutile has relatively high but variable Cr and Cu concentrations with minor Sr, Zn, Ga, Sc and Y. Rutile grains from three eclogite samples have variable Nb and Ta concentrations (Table 11), and relatively high Nb/Ta ratios ranging from 21.9 to 36.4, which are much higher than the chondritic value of 17.5 (Sun and McDonough, 1989; Jochum and Stolz, 1997; Xiao et al., 2006b). In contrast, rutile from veins has variable Nb (83.6–453.2 ppm) and Ta (4–23 ppm) concentrations, and lower Nb/Ta ratios (6.2–16.4, with a mean value of 12.1) than the chondrite and host eclogite. REE concentrations of most rutile grains are at or below the detection limits. In order to test the homogeneity of the trace element distribution in rutile, multiple analyses on four coarsegrained rutile grains were carried out in addition to the profile analysis. All results show no distinct trace element zoning with regard to Nb and Ta concentrations and Nb/Ta. 6.5. Other minerals Apatite in eclogites and veins contains relatively high Sr and REEs, and low Y contents (Table 12). Its REE patterns show enrichment in REE, especially MREE. Some grains show negative Ce anomalies (Fig. 4F). Kyanite from eclogite is similar to that from veins in terms of low V, Cr and

Ga contents (Table 13). A phengite grain from the eclogite CZ7E sample has a high SiO2 content (55.5 wt%, Si = 3.5 pfu, O = 11), and very high Ba (1409 ppm), Rb (280 ppm) and Cs (6.2 ppm), but minor Sr (52 ppm), V (165 ppm), Zn (57 ppm), Cr (57 ppm), Ni (65 ppm), Cu (33 ppm) and Ga (89 ppm) contents. REE contents of kyanite and phengite are below the detection limits. 6.6. Trace element behavior of UHP minerals Based on the above descriptions, the distribution and concentrations of trace elements in UHP minerals from the Chizhuang UHP veins and host eclogites can be summarized as follows: (1) The major minerals, garnet and omphacite, are the primary hosts for only some of trace elements. Garnet holds more than 90% of Y, considerable amounts of Zn, Co, V and HREE, and contributes significantly to the HREE budget, i.e. its HREE contents are higher than those of the whole-rock (Figs. 4 and 5). In contrast, omphacite contains significant amounts of Sr, V, Zn, Ni and Cr, but insignificant amounts of HFSE and minor REE, with REE patterns of MREE enrichment and LREE and HREE depletion (Figs. 4 and 5). Phengite is the main host of the LILE. Zoisite is second to allanite in terms of abundance of REE and has relatively high but variable Sr, Ba, V, Cr and Pb contents. The eclogitic zoisite has higher REE contents than that of the whole-rocks,

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Z.-M. Zhang et al. / Geochimica et Cosmochimica Acta 72 (2008) 3200–3228

Table 4 The trace element compositions of garnets from the eclogites and kyanite–quartz veins Sample: Comment: Rock:

CZ1E cz1-5 Eclogite

CZ7E cz7-2 Eclogite

CZ7E cz7-9 Eclogite

CZ9V cz9-3-1 Vein

CZ9V cz9-4-4 Vein

CZ14E cz14-7 Eclogite

CZ19E cz19-5 Ecloigte

CZ25E cz25-4 Ecloigte

CZ25E cz25-5 Ecloigte

Sr Zr Ba V Zn Cr Co Ni Cu Ga Rb Mo Sc Y

0.448 1.922 0.036 46.710 54.390 177.850 72.330 4.980 0.222 8.070 0.027 0.331 65.160 9.170

0.068 1.872 0.124 35.020 122.530 58.920 92.460 1.680 0.513 6.830 0.143 0.214 36.250 15.220

3.450 1.461 0.368 49.290 81.070 35.700 51.090 1.760 0.868 8.710 0.056 0.120 20.550 8.620

0.141 1.155 <0.041 17.210 216.450 12.480 70.640 <0.311 <0.171 12.990 0.040 0.232 70.640 200.070

0.149 1.740 <0.040 78.270 207.290 10.500 57.730 1.340 0.222 15.540 <0.031 0.240 68.540 50.590

0.297 1.600 0.061 31.980 50.060 880.890 96.070 2.530 1.340 3.560 0.226 0.117 81.700 13.200

2.252 3.960 4.980 44.860 93.570 342.770 148.870 36.640 3.430 12.470 3.260 0.049 56.030 29.810

0.218 1.177 0.198 150.490 86.280 97.230 50.080 4.860 1.750 8.420 <0.021 0.403 36.640 27.260

0.127 0.610 0.029 91.250 88.740 78.110 51.730 4.180 0.659 8.420 <0.012 0.036 40.640 26.030

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

<0.004 <0.005 <0.004 <0.022 0.024 0.068 0.249 0.141 1.149 0.431 0.985 0.190 1.135 0.216

<0.008 <0.009 0.002 <0.030 0.050 0.036 0.202 0.141 1.661 0.712 1.845 0.403 2.330 0.470

0.082 0.196 0.039 0.296 0.623 0.778 1.306 0.288 1.511 0.373 0.977 0.188 1.116 0.200

0.049 0.386 <0.006 0.091 0.056 0.043 0.849 0.848 14.570 8.770 30.890 7.450 50.080 10.560

<0.010 <0.004 <0.004 <0.021 <0.029 0.040 0.396 0.263 3.520 1.930 6.500 1.400 8.210 1.530

0.052 0.060 0.008 <0.022 <0.030 0.016 0.047 0.094 1.114 0.579 2.430 0.508 3.670 0.757

0.220 0.014 0.055 0.234 0.078 0.207 0.762 0.373 4.190 1.416 3.420 0.588 2.360 0.577

0.008 0.035 0.014 0.297 0.646 0.774 3.040 0.943 5.210 1.269 2.820 0.463 2.760 0.470

0.015 0.080 0.011 0.268 0.609 0.636 2.415 0.768 4.770 1.222 2.652 0.475 2.440 0.445

and therefore is a very important host of REE. Its REE patterns are similar to those of the whole-rocks, especially imitating the positive Eu anomalies of the whole-rocks (Figs. 4 and 5). Apatite has relatively high REE contents, with REE patterns of MREE enrichment and LREE and HREE depletion (Fig. 4F). (2) Rutile contains almost all of the bulk rock Ti, Nb and Ta. (3) Vein allanite contains the highest LREE contents, having total REE contents of more than 7.8–10.5 wt% with pronounced enrichment of LREE and depletion of HREE (Fig. 4D). In addition, allanite has the highest contents of Th, U and Pb among all minerals studied here, and relatively high Sr, Ba, V, Zn and Ga. 7. FLUID INCLUSIONS Petrographic examination shows that fluid inclusions occur mainly in allanite, zoisite, and kyanite, as well as in vein quartz. Based on the composition of fluid inclusions and their textural relationships with host minerals, five types of fluid inclusions were recognized. Type I inclusions are multiphase solid (MS) inclusions, consisting of minerals ± a cavity with or without a visible fluid phase. They are present locally in kyanite and zoisite and occur randomly or in clusters (Fig. 7A). Most MS inclusions have polygonal to tubular shapes and some are irregularly shaped, varying in size between 10 and 50 lm. EDS and Raman analyses indicated that type I inclusions

commonly have a daughter mineral association of paragonite (Prg) + an unknown phase (X) ± corundum (Crn) ± magnetite (Mag) ± anhydrite (Anh) ± carbonate ± pyrite (Py) (Fig. 7A and B). The paragonite contains 6.3–6.7 wt% of Na2O, 40.3–41.5 wt% of Al2O3 and 48.6– 49.8 wt% of SiO2; the corundum contains up to 98.15 wt% Al2O3. These two minerals show characteristic Raman shift peaks at around 700–705 cm 1 for paragonite and 416 cm 1 for corundum. Raman analyses of highly birefringent minerals show distinct peaks at 1017 cm 1 for anhydrite and 1088  1090 cm 1 for carbonate (calcite and/or siderite). Two opaque minerals were confirmed to be magnetite (669 cm 1) and pyrite (374 cm 1). The cavity (V) suggesting the former presence of a fluid phase accounts generally for about 10% of the inclusion volume. Type II inclusions are multi-solid fluid inclusions containing solids plus liquid and vapor phases with the solids accounting for 30–70 vol% (Fig. 7C–F). These inclusions occur in the cores of allanite and zoisite crystals either as isolated individuals or in clusters parallel to the c-axis of the host mineral, or as intragranular trails within individual crystals, mostly varying in size from <10 to 50 lm. EDS and Raman analyses indicated that the association of paragonite (or muscovite) + anhydrite + calcite ± apatite (Ap) ± celestite (Cls) ± quartz is present in type II inclusions (Fig. 7C–E). In addition, an unknown mineral (X) was detected by Raman analysis to have OH in its structure. The liquid and gas phases consist dominantly of

Table 5 Major element compositions of the omphacite from the eclogites and veins CZ1E cz1-4 Eclogite

CZ2V cz2-2-5 Vein

CZ3V cz3-13 Vein

CZ6V cz6-1 Vein

CZ6V cz6-4 Vein

SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O K2O Total

55.98 0.04 10.00 0.05 2.05

56.13 0.07 13.55 0.04 3.26

56.15 0.08 12.41

9.78 15.88 5.28 0.00 99.07

6.57 10.73 8.33 0.00 98.71

7.58 12.29 7.65 0.00 99.91

56.22 0.00 10.32 0.02 3.90 0.03 8.95 13.92 6.91 0.02 100.29

3.74

CZ7E cz7-1 Eclogite

CZ14E cz14-3 Eclogite

CZ18V cz18-1-23 Vein

CZ18V cz18-1-24 Vein

CZ19E cz19-2 Eclogite

CZ20V cz20-1-14 Vein

CZ20V cz20-1-17 Vein

CZ20V cz20-2-1 Vein

CZ25E cz25-8 Eclogite

CZ25E cz25-9 Eclogite

55.64 0.02 10.28 0.07 3.79 0.02 9.10 14.31 6.81

55.88 0.07 14.74 0.03 3.41 0.01 6.17 10.45 8.81

55.43 0.11 14.79

55.64 0.06 14.63 3.27

55.41 0.05 11.79 0.02 3.53

99.56

6.21 10.11 8.68 0.00 98.60

55.13 0.09 14.72 0.05 3.34 0.00 6.23 10.68 8.76

54.69 0.13 11.73 0.06 3.35

5.96 9.94 8.87

55.58 0.04 14.54 0.03 3.38 0.00 6.26 10.57 8.67 0.01 99.08

55.52

3.20

55.07 0.02 10.14 0.04 2.31 0.02 10.42 16.14 5.49

100.04

54.94 0.00 8.41 0.12 2.09 0.04 11.61 17.82 4.61 0.01 99.65

8.11 13.05 7.17 0.02 98.30

7.96 12.93 7.09 0.01 98.79

98.30

99.65

14.86 3.51 0.01 6.04 10.43 8.92 0.01 99.30

99.00

Si Ti Al Cr Fe3+ Fe2+ Mn Mg Ca Na K Cations

2.011 0.001 0.423 0.001 0.000 0.062 0.000 0.524 0.611 0.368 0.000 4.000

1.999 0.002 0.569 0.001 0.004 0.093 0.000 0.349 0.409 0.575 0.000 4.000

1.983 0.002 0.517 0.000 0.036 0.074 0.000 0.399 0.465 0.524 0.000 4.000

1.984 0.000 0.429 0.001 0.075 0.040 0.001 0.471 0.526 0.473 0.001 4.000

1.968 0.001 0.428 0.002 0.099 0.013 0.001 0.480 0.542 0.467 0.000 4.000

1.967 0.002 0.611 0.001 0.051 0.049 0.000 0.324 0.394 0.601 0.000 4.000

1.961 0.000 0.354 0.003 0.040 0.023 0.001 0.618 0.681 0.319 0.000 4.000

1.974 0.003 0.621 0.000 0.038 0.057 0.000 0.316 0.379 0.612 0.000 4.000

1.977 0.002 0.613 0.000 0.027 0.070 0.000 0.329 0.385 0.598 0.000 4.000

1.958 0.001 0.425 0.001 0.034 0.035 0.001 0.552 0.615 0.379 0.000 4.000

1.966 0.001 0.606 0.001 0.053 0.047 0.000 0.330 0.401 0.595 0.000 4.000

1.957 0.000 0.617 0.000 0.077 0.026 0.000 0.317 0.394 0.610 0.000 4.000

1.950 0.002 0.614 0.001 0.080 0.019 0.000 0.329 0.405 0.601 0.000 4.000

1.963 0.004 0.496 0.002 0.069 0.032 0.000 0.434 0.502 0.499 0.001 4.000

1.983 0.001 0.497 0.001 0.025 0.080 0.000 0.425 0.496 0.492 0.000 4.000

Jd Di Hd

0.432 0.559 0.066

0.578 0.328 0.088

0.522 0.396 0.074

0.430 0.486 0.041

0.425 0.523 0.014

0.614 0.344 0.052

0.354 0.657 0.024

0.626 0.324 0.059

0.623 0.323 0.069

0.428 0.582 0.037

0.609 0.352 0.051

0.615 0.362 0.030

0.610 0.381 0.022

0.496 0.467 0.034

0.503 0.422 0.080

Fluids in deeply subducted continent

Sample: Comment: Rock:

3211

3212

Table 6 Trace element compositions of the omphacite from the eclogites and veins CZ1E cz1-4 Eclogite

CZ2V cz2-2-5 Vein

CZ3V cz3-13 Vein

CZ6V cz6-1 Vein

CZ6V cz6-4 Vein

CZ7E cz7-1 Eclogite

CZ14E cz14-3 Eclogite

CZ18V cz18-1-23 Vein

CZ18V cz18-1-24 Vein

CZ19E cz19-2 Eclogite

CZ20V cz20-1-14 Vein

CZ20V cz20-1-17 Vein

CZ20V cz20-2-1 Vein

CZ25E cz25-8 Eclogite

CZ25E cz25-9 Eclogite

Sr Zr V Zn Cr Co Ni Cu Ga Rb Hf Pb Sc Y

53.31 1.98 91.78 48.74 245.69 25.92 256.15 22.58 12.47 0.06 0.10 0.49 19.46 0.16

41.27 1.14 484.91 91.78 28.12 19.90 90.10 25.97 37.31 1.54 0.08 0.18 8.85 0.14

44.16 1.43 571.12 115.37 66.42 20.99 97.45 3.99 34.23 0.07 0.13 0.11 17.21 0.14

81.40 1.54 673.86 112.67 163.12 23.76 430.04 3.93 33.28 0.02 0.08 0.45 13.11 0.29

90.45 1.63 624.55 105.60 143.57 22.92 384.53 3.31 30.71 0.10 0.11 0.67 14.04 0.35

38.85 1.20 204.10 77.40 44.21 22.47 61.28 2.78 30.75 <0.02 0.07 0.14 6.17 0.04

64.16 1.58 97.78 41.57 557.09 25.08 252.93 2.86 12.52 0.32 0.07 0.52 19.30 0.16

38.22 1.26 442.73 83.38 36.79 20.05 79.28 2.55 38.24 <0.02 0.11 0.14 8.96 0.15

37.72 1.26 458.84 80.36 36.09 18.77 83.24 3.52 35.36 1.05 0.08 0.18 9.74 0.17

34.60 1.67 63.30 31.07 191.95 21.05 253.81 1.67 10.07 <0.01 0.10 0.24 5.09 0.10

24.71 1.11 428.28 97.56 30.64 21.49 78.17 2.74 33.14 0.02 0.05 0.05 11.99 0.25

36.54 1.28 443.68 100.21 26.54 21.30 82.13 2.95 42.34 <0.02 0.07 0.30 8.93 0.20

39.33 1.16 504.17 99.80 38.01 20.91 89.61 35.19 40.81 <0.02 0.07 0.14 9.82 0.16

37.31 1.25 370.33 65.77 114.04 16.06 117.25 15.54 19.66 <0.01 0.12 0.31 8.73 0.20

38.95 1.02 360.64 69.99 93.16 17.28 119.15 17.41 20.58 <0.01 0.03 0.33 7.94 0.20

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

0.020 0.012 0.004 0.104 0.020 0.087 0.028 0.014 0.023 0.006 0.007 0.004 <0.016 <0.001

0.025 0.097 0.037 0.237 0.146 0.083 0.098 0.011 0.032 0.003 <0.006 0.003 <0.014 <0.003

0.009 0.006 0.004 <0.013 <0.015 <0.006 0.045 0.005 0.004 0.004 0.018 0.003 0.011 <0.003

0.163 1.220 0.330 2.263 0.725 0.260 0.325 0.023 0.101 0.019 0.012 <0.002 <0.021 <0.004

0.188 1.162 0.325 2.150 0.743 0.265 0.393 0.041 0.089 0.008 0.029 <0.003 <0.018 <0.003

0.008 0.037 0.015 0.066 0.044 0.028 0.026 0.009 0.015 0.003 <0.007 0.002 <0.022 <0.004

0.076 0.320 0.028 0.029 <0.014 0.013 0.015 0.005 0.013 0.005 0.028 <0.002 <0.020 0.005

0.039 0.249 0.047 0.216 0.112 0.065 0.093 0.015 0.045 0.007 0.013 <0.002 <0.017 0.005

0.019 0.097 0.033 0.206 0.142 0.066 0.119 0.011 0.034 0.007 0.017 <0.004 <0.013 <0.002

<0.003 0.011 0.006 0.043 0.020 0.008 0.018 0.004 0.028 0.007 0.011 <0.003 <0.006 0.001

<0.007 0.010 0.003 0.054 0.042 0.054 0.041 0.007 0.069 0.013 0.016 0.002 0.018 <0.003

0.009 0.093 0.022 0.147 0.108 0.060 0.081 0.010 0.046 0.011 0.009 <0.004 0.018 <0.002

0.029 0.107 0.042 0.229 0.186 0.091 0.126 0.010 0.056 0.010 <0.009 0.003 <0.018 <0.004

0.073 0.521 0.134 0.862 0.405 0.153 0.246 0.023 0.065 0.008 0.009 0.000 0.002 <0.001

0.060 0.559 0.153 0.901 0.346 0.135 0.217 0.028 0.075 0.007 0.005 0.004 <0.012 <0.001

Z.-M. Zhang et al. / Geochimica et Cosmochimica Acta 72 (2008) 3200–3228

Sample: Comment: Rock:

Table 7 Major and trace element compositions of the allanite from the allanite–quartz veins Sample: CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ20V CZ20V CZ20V CZ20V CZ20V CZ20V Comment: cz18-1-10 cz18-1-11 cz18-1-12 cz18-1-13 cz18-1-14 cz18-1-15 cz18-1-16 cz18-1-17 cz18-1-19 cz18-1-20 cz18-1-21 cz20-1-4 cz20-1-5 cz20-1-6 cz20-1-7 cz20-1-8 cz20-1-9

Si AlIV AlVI Fe3+ Ti Mg Ca Na K V Zn Y Sr Th

35.75 0.09 25.98 5.31 0.78 20.49 0.05 0.01 0.18 0.06 0.08 0.01 2.75 1.36 0.33 1.19 0.18 0.05 0.01 0.80 0.02 95.48 2.967 0.033 2.506 0.331 0.006 0.096 1.822 0.008 0.001 0.005 0.001 0.000 0.038 0.003

35.52 0.00 26.13 5.26 0.73 21.11 0.04 0.14 0.05 0.08 0.01 2.79 1.37 0.33 1.18 0.17 0.05 0.01 0.85 0.02 95.86 2.944 0.056 2.494 0.328 0.000 0.090 1.874 0.006 0.000 0.005 0.001 0.000 0.041 0.003

35.51 0.09 26.10 5.32 0.77 20.71 0.01 0.01 0.13 0.05 0.08 0.01 2.81 1.40 0.33 1.17 0.17 0.05 0.01 0.83 0.02 95.60 2.948 0.052 2.500 0.332 0.006 0.095 1.842 0.002 0.001 0.005 0.001 0.000 0.040 0.002

35.10 0.05 25.71 5.48 0.76 20.34 0.07 0.00 0.17 0.06 0.08 0.01 2.78 1.37 0.33 1.19 0.18 0.05 0.01 0.78 0.02 94.54 2.948 0.052 2.491 0.346 0.003 0.095 1.831 0.011 0.000 0.005 0.001 0.000 0.038 0.003

35.24 0.08 25.95 5.43 0.74 20.72 0.06 0.01 0.12 0.05 0.08 0.01 2.60 1.30 0.31 1.11 0.17 0.05 0.01 0.83 0.02 94.89 2.943 0.057 2.495 0.341 0.005 0.092 1.854 0.010 0.001 0.005 0.001 0.000 0.040 0.002

35.32 0.07 25.75 5.45 0.74 20.72 0.09 0.00 0.13 0.05 0.08 0.01 2.69 1.36 0.32 1.14 0.17 0.05 0.01 0.84 0.02 95.01 2.951 0.049 2.484 0.342 0.004 0.092 1.855 0.015 0.000 0.005 0.001 0.000 0.041 0.002

35.00 25.76 5.77 0.63 20.96 0.09 0.00 0.13 0.05 0.08 0.01 2.52 1.26 0.30 1.10 0.17 0.05 0.01 0.78 0.02 94.70 2.933 0.067 2.476 0.364 0.000 0.079 1.882 0.015 0.000 0.005 0.001 0.000 0.038 0.002

35.01 0.06 25.75 5.38 0.87 20.33 0.03 0.00 0.18 0.05 0.08 0.01 2.96 1.47 0.36 1.28 0.19 0.05 0.01 0.81 0.02 94.91 2.938 0.062 2.483 0.339 0.004 0.109 1.828 0.005 0.000 0.005 0.001 0.000 0.039 0.003

35.51 0.10 25.45 5.33 0.73 20.45 0.08 0.01 0.14 0.05 0.08 0.01 2.75 1.38 0.33 1.18 0.18 0.05 0.01 0.84 0.02 94.69 2.976 0.024 2.488 0.336 0.006 0.091 1.836 0.013 0.001 0.005 0.001 0.000 0.041 0.003

35.49 0.09 25.99 5.35 0.76 20.64 0.06 0.01 0.13 0.05 0.09 0.01 2.64 1.32 0.32 1.14 0.17 0.05 0.01 0.80 0.02 95.16 2.954 0.046 2.502 0.335 0.006 0.094 1.841 0.010 0.001 0.006 0.001 0.000 0.039 0.002

36.18 0.07 26.87 5.00 0.53 21.81 0.00 0.00 0.15 0.05 0.08 0.02 2.68 1.35 0.32 1.17 0.18 0.06 0.01 0.89 0.02 97.44 2.943 0.057 2.517 0.306 0.004 0.064 1.901 0.000 0.000 0.005 0.001 0.001 0.042 0.003

35.28 0.07 25.87 5.31 0.82 20.61 0.06 0.01 0.15 0.05 0.09 0.01 2.87 1.38 0.34 1.26 0.19 0.05 0.01 0.81 0.02 95.28 2.944 0.056 2.486 0.333 0.004 0.102 1.843 0.010 0.001 0.006 0.001 0.000 0.039 0.003

35.02 0.09 25.77 5.15 0.75 20.55 0.05 0.13 0.05 0.08 0.01 2.82 1.38 0.33 1.19 0.18 0.05 0.01 0.79 0.02 94.42 2.945 0.055 2.497 0.326 0.006 0.094 1.852 0.008 0.000 0.005 0.001 0.000 0.039 0.002

35.12 0.05 25.28 5.86 0.68 20.29 0.04 0.01 0.14 0.06 0.08 0.01 2.76 1.38 0.33 1.19 0.18 0.05 0.01 0.86 0.02 94.40 2.959 0.041 2.468 0.371 0.003 0.085 1.832 0.007 0.001 0.005 0.001 0.000 0.042 0.003

35.09 0.03 25.70 5.36 0.78 20.33 0.06 0.22 0.06 0.08 0.01 3.34 1.67 0.39 1.41 0.20 0.06 0.01 0.87 0.02 95.68

35.06 0.07 25.47 5.43 0.78 20.60 0.01 0.00 0.20 0.07 0.08 0.01 3.19 1.56 0.38 1.35 0.20 0.06 0.01 0.83 0.02 95.39

35.29 0.08 25.52 5.57 0.81 20.59 0.05 0.17 0.06 0.09 0.01 2.82 1.38 0.34 1.22 0.19 0.05 0.01 0.83 0.02 95.11

2.937 2.941 2.952 0.063 0.059 0.048 2.470 2.457 2.466 0.337 0.342 0.350 0.002 0.004 0.005 0.097 0.098 0.101 1.823 1.851 1.846 0.010 0.002 0.008 0.000 0.000 0.000 0.005 0.005 0.006 0.001 0.001 0.001 0.000 0.000 0.000 0.042 0.040 0.040 0.004 0.004 0.003 (continued on next page)

Fluids in deeply subducted continent

SiO2 TiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O ThO2 UO2 V2O3 Y2O3 Ce2O3 La2O3 Pr2O3 Nd2O3 Sm2O3 Gd2O3 ZnO SrO PbO Total

3213

0.001 0.086 0.043 0.010 0.036 0.005 0.001 0.000 0.001 0.098 0.048 0.012 0.040 0.006 0.002 0.000 0.001 0.102 0.052 0.012 0.042 0.006 0.002 0.000 0.001 0.085 0.043 0.010 0.036 0.005 0.001 0.000 0.001 0.087 0.043 0.010 0.036 0.005 0.001 0.000 0.001 0.088 0.042 0.010 0.038 0.005 0.001 0.000 0.001 0.080 0.040 0.009 0.034 0.005 0.002 0.000 0.001 0.080 0.040 0.010 0.034 0.005 0.001 0.000 0.001 0.084 0.043 0.010 0.035 0.005 0.001 0.000 0.001 0.091 0.045 0.011 0.038 0.005 0.001 0.000 0.001 0.077 0.039 0.009 0.033 0.005 0.001 0.000 0.001 0.082 0.042 0.010 0.034 0.005 0.001 0.000

H2O. In comparison to rare type I inclusions, type II inclusions are very abundant in the UHP vein minerals and occupy up to 2–5% of the host mineral volume. Type III inclusions are mixed H2O–CO2 inclusions, which contain two or three phases at room temperature. In general, CO2 phases account for 10–20 vol% of the inclusion cavity. These inclusions are tube-shaped or rounded, and occur usually as trails along intragranular fractures in kyanite crystals. Rarely, type III inclusions coexist with MS inclusions. Type IV inclusions are complex brine-bearing aqueous inclusions containing halite + calcite ± anhydrite ± opaque minerals, and occur mainly in quartz as trails along intragranular fractures. Type V inclusions are two-phase or monophase aqueous inclusions and usually occur as trails along transgranular fractures in quartz and zoisite. The abundant multi-solid fluid inclusions (type II) and rare MS inclusions (type I) occur individually or in clusters parallel to the c-axis of host minerals or along intragranular fractures, in the cores of kyanite, allanite and zoisite crystals. They were trapped as primary or pseudosecondary inclusions during growth of host minerals and may represent the compositions of vein-forming UHP fluids. Type III inclusions occur mainly as intragranular trails and coexist with MS inclusions in kyanite, implying possibly the immiscibility of originally homogeneous silicate-rich aqueous fluids with significant amounts of CO2 (and S species) present at a certain stage of UHP metamorphism. The type IV and type V inclusions occurring along transgranular fractures in zoisite are secondary. However, other type IV and type V inclusions that occur in intragranular and transgranular fractures, respectively, in quartz, are pseudosecondary and secondary inclusions with respect to the host mineral. Because the quartz was assumed to be recrystallized after coesite during the exhumation of UHP rocks, the type IV and V inclusions may only represent the fluids post-date UHP metamorphism. 8. DISCUSSION

0.001 0.083 0.042 0.010 0.035 0.005 0.001 0.000

0.001 0.085 0.042 0.010 0.035 0.005 0.001 0.000

0.001 0.085 0.043 0.010 0.035 0.005 0.001 0.000

0.001 0.085 0.042 0.010 0.036 0.005 0.001 0.000

0.001 0.079 0.040 0.009 0.033 0.005 0.001 0.000

8.1. Origin of the UHP veins

U Ce La Pr Nd Sm Gd Pb

Sample: CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ20V CZ20V CZ20V CZ20V CZ20V CZ20V Comment:cz18-1-10 cz18-1-11 cz18-1-12 cz18-1-13 cz18-1-14 cz18-1-15 cz18-1-16 cz18-1-17 cz18-1-19 cz18-1-20 cz18-1-21 cz20-1-4 cz20-1-5 cz20-1-6 cz20-1-7 cz20-1-8 cz20-1-9

Z.-M. Zhang et al. / Geochimica et Cosmochimica Acta 72 (2008) 3200–3228

Table 7 (continued)

3214

Formation conditions of the Sulu eclogites have been widely discussed (e.g., Hirajima et al., 1990; Enami et al., 1993; Zhang et al., 1994, 1995). Based on the studies of various eclogites from the CCSD main drill hole, P–T estimates of 3.0–4.5 GPa and 700–850 °C were obtained using geothermobarometers relevant to the eclogitic garnet, omphacite and phengite assemblage (Zhang et al., 2006c). For a Chizhuang phengite- and kyanite-bearing eclogite sample CZ7E, the P–T conditions of 3.0 GPa and 760 °C were estimated using the geothermobarometry of phengite–kyanite–coesite eclogite (Ravna and Milke, 2001), assuming the Fe3+ in omphacite is equal to Na–AlVI. In addition, assuming P = 3.0 GPa, temperatures of 688– 887 °C (with a mean value of 768 °C) were obtained for other phengite-free eclogites using the Fe2+–Mg exchange thermometer of Krogh (1988). This result together with the occurrences of coesite or its pseudomorph in eclogitic garnet, omphacite and zircon demonstrates conclusively

Table 8 Trace element compositions of the allanite from the allanite–quartz veins Sample: CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ18V CZ20V CZ20V CZ20V CZ20V CZ20V CZ20V Comment: cz18-1-10 cz18-1-11 cz18-1-12 cz18-1-13 cz18-1-14 cz18-1-15 cz18-1-16 cz18-1-17 cz18-1-19 cz18-1-20 cz18-1-21 cz20-1-4 cz20-1-5 cz20-1-6 cz20-1-7 cz20-1-8 cz20-1-9

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

6729.05 3.48 32.81 551.62 103.02 44.57 16.58 30.21 0.28 113.72 0.19 130.09 1608.09 502.20 13.85 53.61

7157.74 4.10 33.65 574.06 102.20 45.30 16.46 29.20 <0.14 121.88 0.14 125.39 1223.71 457.36 13.72 52.95

7045.14 3.82 38.70 552.33 103.38 43.71 16.93 28.56 1.25 118.61 0.15 123.78 1143.49 434.70 13.39 52.41

6567.82 4.61 45.93 575.62 106.43 44.49 17.01 24.39 0.32 118.94 0.26 125.18 1494.07 523.28 15.31 56.72

6983.42 3.87 34.78 547.59 94.36 44.99 15.63 26.15 <0.132 118.29 0.15 113.78 1060.51 427.74 13.82 54.70

11621.05 11692.16 11960.52 11670.54 11049.33 23470.86 23855.58 23981.16 23702.25 22233.58 2815.31 2832.35 2831.14 2832.71 2653.86 10202.24 10099.72 10055.51 10185.55 9546.00 1530.43 1505.69 1498.99 1543.05 1459.76 390.37 390.87 384.36 396.45 377.16 458.89 452.62 448.51 459.02 435.46 22.40 22.15 21.55 22.55 21.88 32.46 31.81 31.15 32.71 32.13 2.95 2.90 2.88 3.09 2.94 5.22 5.44 5.28 5.57 5.26 0.18 0.18 0.17 0.22 0.20 0.64 0.76 0.62 0.68 0.73 0.05 0.06 0.05 0.08 0.05

7144.86 4.12 35.40 558.44 91.22 47.29 16.24 22.51 2.14 118.81 0.16 113.10 1099.14 422.81 14.88 55.08

6562.98 3.61 31.58 560.41 90.70 45.39 15.12 24.86 15.51 121.94 0.16 114.19 1180.02 467.99 14.39 58.15

6845.39 3.46 32.04 551.85 98.05 44.04 17.09 30.60 0.16 113.80 0.14 126.15 1620.02 459.80 13.44 48.57

7085.74 4.38 32.95 547.34 90.76 42.52 16.19 28.63 <0.166 122.01 0.19 124.09 1236.77 474.09 13.72 58.60

11586.70 10719.02 12561.49 11765.09 23000.91 21521.01 25246.07 23450.99 2725.66 2603.39 3034.39 2812.04 9758.03 9418.02 10969.21 10118.99 1476.55 1459.00 1614.97 1547.23 374.92 379.89 402.37 397.34 446.98 446.24 463.98 475.10 21.72 22.46 21.33 23.42 32.44 33.96 29.21 34.90 2.89 3.17 2.58 3.17 5.20 5.29 5.19 5.70 0.15 0.20 0.15 0.20 0.62 0.70 0.70 0.67 0.06 0.08 0.05 0.08

6805.55 3.94 40.62 639.27 98.45 44.39 16.72 24.39 42.62 113.70 0.22 108.92 1119.29 478.54 13.64 61.14

7493.45 4.17 39.12 574.69 93.00 42.45 15.69 28.83 7.93 122.15 0.19 140.54 1280.42 479.17 15.94 69.52

6863.28 3.42 33.98 586.61 105.67 48.40 16.70 31.49 0.50 126.40 0.13 135.76 1330.31 483.14 14.74 59.06

6674.07 3.67 36.00 540.81 102.83 43.96 15.65 25.38 0.33 122.44 0.17 124.79 1173.95 465.58 14.61 57.42

7278.01 3.54 41.52 529.71 106.45 53.23 15.73 27.48 7.95 121.48 0.18 138.04 1190.67 520.82 14.77 63.52

7316.93 2.89 38.81 538.15 119.18 48.16 18.69 32.33 2.64 125.11 0.15 150.23 1896.04 517.90 11.85 53.22

7053.42 3.25 36.89 529.16 118.64 54.06 18.68 28.28 3.21 124.05 0.15 145.92 1747.00 585.36 12.42 60.64

7043.77 5.37 38.55 590.82 104.01 54.31 16.58 27.52 3.62 128.96 0.22 131.07 1453.25 560.16 16.00 62.18

11279.46 11497.79 11764.98 11774.84 11763.24 14220.15 13309.29 11773.90 22528.22 22842.20 24523.76 24088.71 23527.92 28477.35 27224.93 24098.56 2698.87 2756.94 2947.61 2811.08 2819.07 3365.75 3257.33 2880.10 9765.59 10058.86 10783.29 10171.74 10172.29 12081.79 11571.96 10486.69 1504.55 1555.12 1630.09 1512.40 1569.90 1746.37 1757.58 1609.39 392.97 404.66 410.65 380.93 402.60 426.35 436.69 409.56 465.63 480.34 448.02 425.70 460.40 486.71 501.31 459.30 23.27 24.56 23.04 21.88 24.90 24.11 25.98 24.55 34.62 38.79 34.70 34.17 39.96 34.54 38.88 37.63 3.38 3.72 3.33 3.25 3.72 3.02 3.53 3.59 5.45 5.77 5.18 5.54 5.78 5.22 5.77 5.50 0.24 0.25 0.24 0.24 0.25 0.18 0.22 0.22 0.91 0.92 0.81 0.82 1.01 0.69 0.83 0.88 0.08 0.09 0.08 0.07 0.09 0.07 0.07 0.07

Fluids in deeply subducted continent

Sr Zr Ba V Zn Cr Co Ni Cu Ga Hf Pb Th U Sc Y

3215

3216

Table 9 Major element compositions of the zoisite and epidote from the eclogites and veins CZ1E cz1-6 Eclogite Zo

CZ3V cz3-15 Vein Zo

CZ3V cz3-16 Vein Zo

CZ4V cz4-1-7 Vein Zo

CZ7E cz7-5 Eclogite Zo

CZ7E cz7-6 Eclogite Zo

CZ9V cz09-1-1 Vein Ep

CZ9V cz09-1-3 Vein Ep

CZ9V cz09-3-4 Vein Zo

CZ14E cz14-1 Eclogite Zo

CZ14E cz14-2 Eclogite Zo

CZ19E cz19-4 Eclogite Zo

CZ20V cz20-1-1 Vein Zo

CZ20V cz20-1-10 Vein Zo

CZ26V cz26-6 Vein Zo

SiO2 TiO2 Al2O3 Cr2O3 Fe2O3 MnO MgO CaO Na2O K2O Total

38.63 0.05 32.30 0.06 1.02 0.04 0.07 24.64 0.03 0.01 98.44

39.09 0.08 30.92 0.04 2.49

38.94 0.07 30.89 0.01 2.67

39.86 0.08 31.82 0.17 1.44

39.18 0.03 31.72 0.03 2.01

38.91 0.07 31.31

37.30 0.07 27.53

38.51 0.06 31.89 0.05 1.72

38.43 0.08 31.53 0.28 1.73

38.54 0.02 31.42 0.01 2.13

37.19 0.12 28.89

38.61 0.06 31.81 0.07 1.54

0.07 24.00 0.04

0.06 24.81 0.02

0.04 24.50 0.03

0.14 25.32 0.00

0.07 25.60 0.01

97.19

96.72

98.37

97.86

98.47

0.06 24.96 0.04 0.00 96.22

0.22 23.84 0.01

97.17

0.11 24.86 0.02 0.01 97.10

38.30 0.03 31.92 0.15 1.24 0.00 0.07 25.19

38.89 0.05 32.65 0.02 1.34

0.06 24.08 0.03

37.40 0.04 28.15 0.01 6.32 0.02 0.20 24.05 0.01 0.01 96.85

Si AlIV AlVI Ti Cr Fe3+ Mg Mn Na Ca K Cations

2.976 0.024 2.907 0.003 0.004 0.059 0.008 0.003 0.004 2.034 0.001 8.023

3.021 0.000 2.814 0.005 0.002 0.145 0.007 0.000 0.004 1.994 0.000 7.992

3.014 0.000 2.816 0.004 0.001 0.155 0.008 0.000 0.006 1.990 0.000 7.994

3.024 0.000 2.843 0.005 0.010 0.082 0.012 0.000 0.003 2.021 0.001 8.001

97.12 2.996 0.004 2.852 0.002 0.002 0.116 0.007 0.000 0.003 2.032 0.000 8.014

2.49 0.03 0.06 24.97

97.28 2.984 0.016 2.812 0.004 0.000 0.144 0.007 0.002 0.000 2.052 0.000 8.021

2.961 0.039 2.586 0.002 0.001 0.376 0.024 0.001 0.002 2.040 0.001 8.033

5.92 0.30 22.64 0.03 0.00 96.70 3.012 0.000 2.618 0.004 0.000 0.359 0.036 0.000 0.005 1.959 0.000 7.993

2.974 0.026 2.875 0.003 0.003 0.100 0.005 0.000 0.004 2.027 0.000 8.017

2.959 0.041 2.818 0.005 0.017 0.100 0.016 0.000 0.000 2.089 0.000 8.045

2.960 0.040 2.865 0.002 0.009 0.072 0.008 0.000 0.000 2.086 0.000 8.042

2.952 0.048 2.871 0.003 0.001 0.076 0.008 0.000 0.001 2.082 0.000 8.042

2.975 0.025 2.831 0.001 0.001 0.124 0.007 0.000 0.006 2.064 0.000 8.034

5.16

96.99 2.954 0.046 2.657 0.007 0.000 0.308 0.026 0.000 0.002 2.029 0.000 8.029

0.06 25.11 0.01 0.01 97.50 2.972 0.028 2.856 0.003 0.004 0.089 0.007 0.000 0.001 2.071 0.001 8.032

Z.-M. Zhang et al. / Geochimica et Cosmochimica Acta 72 (2008) 3200–3228

Sample: Comment: Rock: Mineral:

Table 10 Trace element compositions of the zoisite and epidote from the eclogites and veins CZ1E cz1-6 Eclogite Zo

CZ3V cz3-15 Vein Zo

CZ3V cz3-16 Vein Zo

CZ4V cz4-1-7 Vein Zo

CZ7E cz7-5 Eclogite Zo

CZ7E cz7-6 Eclogite Zo

CZ9V cz09-1-1 Vein Ep

CZ9V cz09-1-3 Vein Ep

CZ9V cz09-3-4 Vein Zo

CZ14E cz14-1 Eclogite Zo

CZ14E cz14-2 Eclogite Zo

CZ19E cz19-4 Eclogite Zo

CZ20V cz20-1-1 Vein Zo

CZ20V cz20-1-10 Vein Zo

CZ26V cz26-6 Vein Zo

Sr Zr Ba V Zn Cr Co Ni Cu Ga Hf Pb Th U Sc Y

2550.66 0.75 18.17 98.82 2.12 481.80 0.89 2.59 <0.19 31.95 <0.03 22.12 2.07 0.63 4.51 5.26

13891.39 6.75 47.13 421.29 10.50 52.38 1.26 1.38 0.49 98.15 0.24 33.76 0.45 2.27 12.23 24.59

14193.92 1.95 75.49 355.03 5.93 23.51 0.52 1.09 <0.19 93.53 0.13 37.74 0.42 0.99 4.01 19.73

2532.49 8.17 13.32 209.62 2.23 894.56 1.35 4.08 0.16 36.62 0.25 12.99 2.67 0.71 19.79 11.83

7438.44 0.63 33.96 143.31 4.55 64.17 0.71 0.56 <0.22 70.71 <0.03 76.96 3.33 1.95 2.56 6.06

5289.57 1.05 18.32 164.17 4.67 58.78 0.79 0.97 0.24 78.46 0.05 49.54 1.17 2.71 4.68 7.70

89.21 5.88 107.64 1264.51 547.51 34.28 73.38 208.81 109.48 167.73 0.49 0.61 0.74 0.33 68.63 2.26

72.65 4.19 77.26 1000.62 601.13 48.90 60.74 143.52 32.13 108.18 0.29 0.35 0.32 0.16 62.24 0.70

7040.08 2.47 86.37 40.78 9.95 <2.54 0.89 0.66 <0.18 63.39 0.14 102.70 48.62 5.22 3.47 137.76

1959.82 0.83 10.05 136.54 1.61 2028.74 0.73 2.22 <0.18 29.18 0.03 14.95 0.19 0.18 4.32 5.12

1528.26 2.71 7.93 134.01 2.88 1048.22 0.81 0.66 2.05 35.38 0.09 12.15 2.98 0.93 11.94 11.19

264.18 0.54 1.48 45.50 1.34 124.79 0.42 1.19 0.16 20.15 0.05 2.01 0.13 0.09 2.75 7.37

4240.96 0.50 28.02 322.96 6.57 34.78 0.69 0.39 1.08 95.98 0.04 26.13 22.78 7.51 4.57 33.64

3848.35 5.30 24.78 560.21 21.86 22.66 3.87 2.46 0.56 131.68 0.20 18.07 60.38 45.67 22.43 179.15

3408.74 1.43 21.13 214.80 4.17 199.89 0.75 1.82 1.81 49.17 0.13 41.77 10.25 2.20 7.96 11.24

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

11.55 21.00 2.90 10.34 2.38 1.53 2.43 0.35 1.39 0.27 0.30 0.04 0.17 0.04

21.26 34.17 5.61 36.48 21.54 14.12 24.46 3.37 13.21 1.27 1.14 0.07 0.19 0.01

12.88 35.54 6.44 38.36 18.17 11.20 21.16 3.18 9.19 0.97 0.71 0.04 0.12 <0.01

33.27 67.71 8.65 33.20 7.61 3.17 6.30 1.03 3.68 0.58 0.84 0.09 0.35 0.04

198.19 383.85 46.05 178.16 32.83 20.86 15.87 1.36 2.68 0.29 0.32 0.03 <0.03 0.01

87.93 180.57 23.16 95.01 22.79 16.56 13.37 1.40 3.40 0.39 0.42 0.02 0.10 0.01

0.61 0.09 0.17 0.80 0.03 0.03 0.06 0.02 0.16 0.01 0.11 0.02 0.06 0.06

0.16 0.03 0.07 0.43 0.03 <0.02 0.05 0.01 0.06 0.03 0.03 0.01 <0.04 0.02

391.15 677.14 88.44 293.54 55.62 12.47 42.73 6.98 29.03 6.27 10.72 1.33 5.80 0.78

3.29 7.30 1.00 3.89 1.28 0.79 1.55 0.29 1.27 0.21 0.35 0.03 0.06 0.01

19.87 40.83 5.20 20.80 4.81 2.61 4.30 0.73 2.93 0.52 0.75 0.07 0.16 0.02

1.25 2.29 0.33 1.44 0.38 0.40 1.05 0.42 2.65 0.45 0.39 0.03 0.07 0.00

224.18 512.00 66.62 272.34 55.59 21.38 32.20 4.03 12.03 1.67 1.93 0.17 0.43 0.04

772.52 1816.24 299.73 1388.71 349.40 122.48 213.41 24.19 68.10 8.87 9.65 0.82 2.39 0.25

72.18 134.89 15.66 57.06 10.36 3.72 6.87 0.76 2.82 0.52 0.57 0.08 0.27 0.01

Fluids in deeply subducted continent

Sample: Comment: Rock: Mineral:

3217

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Table 11 Major and trace element compositions of the rutiles from the eclogites and veins CZ1E cz1-1 Eclogite

CZ14E cz14-4 Eclogite

0.01 97.67 0.02 0.15 0.37 0.06 0.01 0.05

0.01 98.11 0.01 0.53 0.41

CZ19E cz19-1 Eclogite

CZ2V cz2-1-1 Vein

CZ2V cz2-2-2 Vein

CZ3V cz3-3 Vein

0.00 97.85

0.04 98.14 0.01 0.02 0.51

0.02 98.01 0.02 0.04 0.68

0.03 0.01

0.05 0.03 0.02

SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O K2O Total

98.35

0.01 99.17

99.52

0.01 98.32

98.76

98.87

Sr Zr V Zn Cr Cu Ga Nb Ta Nb/Ta Hf Pb Mo U Sc Y

3.92 179.51 576.36 8.41 1058.46 2.68 0.23 199.12 8.06 24.70 7.30 3.62 16.74 0.04 4.68 0.30

4.02 115.32 623.51 6.62 3016.77 2.08 0.20 80.81 2.22 36.35 4.24 0.09 2.27 0.01 3.07 0.29

3.34 185.27 485.52 5.59 1134.52 2.16 0.34 247.19 11.28 21.91 9.05 <0.01 2.90 <0.01 1.31 0.35

4.24 154.30 2595.82 8.63 102.81 1.96 1.06 164.27 12.27 13.39 6.57 0.66 28.27 0.28 0.89 0.27

3.93 134.60 2695.15 7.75 101.11 2.13 0.63 148.31 11.02 13.46 6.23 <0.01 27.02 0.22 0.81 0.29

2.96 173.03 2098.51 5.81 126.71 1.06 1.29 159.39 13.94 11.43 7.18 <0.01 28.92 1.12 1.48 0.13

0.04 0.04

98.97 0.06 0.20 0.26 0.01 0.02

0.01 0.45 0.01

CZ3V cz3-5 Vein 0.02 98.13 0.08 0.75 0.02 0.01 0.02

CZ4V cz4-2-1 Vein

CZ18V cz18-1-1 Vein

CZ18V cz18-1-7 Vein

CZ20V cz20-3-1 Vein

CZ20V cz20-3-4 Vein

CZ20V cz20-3-7 Vein

CZ25V cz25-3 Vein

0.02 97.85 0.03 0.16 0.68 0.00

0.01 98.54 0.02 0.03 0.43

0.02 98.12 0.04 0.07 0.38 0.01 0.01 0.01 0.01

0.03 98.82 0.18 0.01 0.30 0.01 0.01 0.03

0.02 98.70 0.02 0.01 0.39 0.02 0.03 0.01

0.06 98.93 0.02 0.04 0.39 0.01 0.02

0.03 97.35 0.02 0.12 0.28

CZ25V cz25-7 Vein 97.32 0.12 0.29 0.03 0.01 0.03

0.03

0.02 0.01

99.01

0.02 98.80

0.02 99.09

98.66

99.40

0.01 99.20

99.48

0.01 97.81

0.01 97.82

2.90 152.68 2158.51 5.13 143.99 1.36 1.03 152.41 12.68 12.02 6.08 0.01 29.11 0.57 1.50 0.15

4.65 141.18 898.94 5.37 723.90 1.84 0.26 250.46 19.43 12.89 5.73 161.98 8.50 0.03 4.27 0.31

3.75 145.77 2233.41 7.60 87.13 2.04 1.28 170.28 17.10 9.96 5.45 0.03 25.94 0.10 1.11 0.23

3.83 139.58 2178.50 8.86 86.64 2.76 1.22 169.29 16.09 10.52 5.51 0.76 26.46 0.11 1.18 0.25

3.51 137.64 2051.81 6.59 101.73 2.47 1.42 196.28 19.34 10.15 5.79 0.01 24.86 0.19 0.98 0.26

3.42 143.96 2053.22 5.80 101.02 1.64 1.07 194.08 20.12 9.65 5.67 0.02 25.10 0.09 0.76 0.26

3.53 135.19 2077.11 7.50 89.84 2.25 0.97 200.03 20.97 9.54 5.75 <0.01 28.58 0.59 0.83 0.29

3.43 125.71 2051.56 7.12 597.13 2.63 0.59 117.96 8.89 13.27 6.48 0.01 18.79 0.11 2.07 0.23

3.48 167.77 1930.00 7.65 751.92 2.10 0.61 125.47 10.53 11.92 7.68 <0.01 21.84 0.35 0.95 0.26

Z.-M. Zhang et al. / Geochimica et Cosmochimica Acta 72 (2008) 3200–3228

Sample: Comment: Rock:

Fluids in deeply subducted continent Table 12 Trace element compositions of apatites from the veins Sample: Comment:

CZ2V cz2-1-4

CZ20V cz20-1-11

CZ20V cz20-1-12

CZ20V cz20-3-15

Sr Zr Ba V Zn Cr Co Ni Pb Th U Sc Y

475.19 0.03 0.32 0.31 0.21 <0.88 0.04 0.11 0.24 0.76 0.52 0.29 15.26

596.14 0.02 0.36 0.52 0.09 2.18 0.01 0.25 0.89 0.15 0.13 0.45 22.82

584.06 0.04 0.35 0.29 <0.08 2.51 0.03 0.12 0.94 0.34 0.29 0.45 23.18

608.38 0.03 0.36 0.40 <0.08 <0.74 0.02 0.24 0.84 0.04 0.20 0.52 21.05

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

9.76 71.15 21.74 165.02 62.25 19.48 34.26 2.67 5.84 0.73 0.80 0.07 0.26 0.03

0.94 3.45 0.77 5.61 3.13 1.50 4.59 0.90 4.20 0.94 1.71 0.23 0.97 0.13

1.76 3.66 0.89 6.41 3.19 1.42 4.72 0.92 4.36 0.96 1.63 0.24 0.95 0.13

0.82 2.95 0.66 4.47 2.70 1.50 4.42 0.88 4.02 0.89 1.64 0.21 0.90 0.13

that the Chizhuang eclogite was formed under UHP metamorphic conditions. Veins containing HP and UHP mineral assemblages are common in eclogites from a number of metamorphic terranes (e.g., Austrheim, 1987; Philippot and Selverstone,

3219

1991; Philippot, 1993; Nadeau et al., 1993; Castelli et al., 1998; Becker et al., 1999; Bruusmann et al., 2000; Scambelluri and Philippot, 2001; Franz et al., 2001; Gao and Klemd, 2001; Svensen et al., 2001; Widmer and Thompson, 2001; Rubatto and Hermann, 2003; Molina et al., 2004). The complex allanite-bearing quartz vein associations, however, have not been reported previously in the DabieSulu orogen. The petrological study described above shows that these veins have variable modal mineral contents, but all primary minerals except quartz in various veins are stable under the coesite–eclogite-facies conditions because the same mineral assemblages with similar mineral compositions occur contemporaneously in the host UHP eclogites. Moreover, coesite inclusions occur in zircon of Aln–Qtz and Ky–Qtz veins, and inclusions of polycrystalline quartz pseudomorph after coesite are present in allanite of the Aln–Qtz veins and in garnet of the Ky–Qtz veins. Therefore, it is concluded that, like the host eclogite, these veins were formed during UHP metamorphism. Previous investigations and this work have shown that the HP and UHP veins contain the same mineral assemblages as the host rocks, which suggests that their filling materials were locally derived. Stable isotope (C–O–H) data have shown that fine-scale heterogeneities were generated during eclogitization and veining in the Alps (Nadeau et al., 1993; Getty and Selverstone, 1994; Vallis et al., 1997; Hermann et al., 2006). In the vicinity of the Maobei body, similar UHP veins are also common in the eclogites. Moreover, oxygen isotope heterogeneities on a cm scale were also recognized in the Zo–Qtz veins hosted in the UHP eclogites (Zhang et al., 2006d). These characteristics require that fluids were internally-buffered by their host rocks and that vein minerals were precipitated from saturated solutions in equilibrium with the surrounding rocks (e.g., Scambelluri and Philippot, 2001). Available data indicate that fluids and/or melts related to the formation of HP and UHP veins were produced by

Table 13 Major and trace element compositions of the kyanite from the eclogites and veins Sample: Comment: Rock: SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Total Sr V Cr Co Ni Cu Ga Sc

CZ1E cz01-2 Eclogite

CZ1E cz1-3 Eclogite

CZ2V cz2-1-3 Vein

CZ2V cz2-2-4 Vein

CZ4V cz4-1-3 Vein

CZ4V cz4-1-8 Vein

36.14 0.03 61.86 0.10 0.34 0.05 0.01 0.02 98.55

36.03

36.35

36.94

36.54

61.94 0.08 0.25 0.03

61.78

0.01 98.36

0.04 0.02 98.67

60.87 0.00 0.43 0.02 0.02 0.00 98.29

62.61 0.15 0.29 0.01 0.01 0.03 99.67

36.76 0.01 62.30 0.16 0.29 0.04 0.00 0.02 99.59

0.18 30.02 372.39 0.10 0.63 0.42 20.18 0.63

0.53 39.25 529.12 0.08 1.20 0.58 15.80 0.43

<0.01 176.03 38.97 0.06 0.69 <0.27 56.20 0.57

<0.02 147.15 45.78 <0.04 <0.37 <0.23 47.00 0.81

<0.01 64.93 844.39 0.06 0.62 18.37 15.46 0.72

<0.01 12.05 225.14 <0.01 0.12 <0.05 2.84 0.13

0.48

CZ7E cz7-4 Eclogite

CZ9V cz09-2-4 Vein

36.67 0.02 62.40 0.06 0.53

36.51 0.04 62.72 0.02 0.48

0.00 99.71 13.48 42.86 70.86 0.12 <0.25 <0.32 28.11 0.68

CZ19E cz19-3 Eclogite

CZ20V cz20-1-15 Vein

CZ20V cz20-3-12 Vein

35.98 0.02 62.63 0.02 0.50 0.03

36.06 0.01 62.55 0.02 0.43

0.01 0.02 99.80

0.02 99.21

0.02 99.10

35.86 0.01 62.57 0.01 0.40 0.00 0.01 0.00 98.89

70.37 <0.21 9.11 0.09 2.75 16.41 35.36 3.52

0.03 22.26 335.24 0.12 0.93 <0.29 22.76 0.31

0.01 98.57 63.02 <0.05 <0.69 1.06 43.32 0.54

0.12 181.43 56.80 <0.06 <0.65 0.45 45.36 0.64

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Z.-M. Zhang et al. / Geochimica et Cosmochimica Acta 72 (2008) 3200–3228 B, CZ7E

A, CZ1E 1000.00

WR Omp Grt Zo

100.00

Sample/Chondrite

Sample/Chondrite

1000.00

10.00 1.00 0.10 0.01

100.00

1.00 0.10

0.01

La Ce Pr Nd SmEu Gd Tb Dy Ho Er TmYb Lu

C, CZ9V

1000.00 WR WR

Grt Grt Grt

Zo Ep Ep

100.00 10.00 1.00 0.10 0.01

Sample/Chondrite

Sample/Chondrite

1000.00

Grt Zo Zo Zo

10.00

La Ce Pr Nd SmEu Gd Tb Dy Ho Er TmYb Lu

10000.00

WR Omp Omp Grt

100.00

D, CZ14E WR Omp Grt

Zo Zo Zo

10.00

1.00 0.10 0.01

La Ce Pr Nd SmEu Gd Tb Dy Ho Er Tm Yb Lu

La Ce Pr Nd SmEu Gd Tb Dy Ho Er TmYb Lu

Fig. 5. Chondrite-normalized REE patterns of the minerals and their host whole-rocks (WR).

dehydration of hydrous minerals, such as zoisite and phengite during prograde UHP metamorphism (e.g., Schmidt and Poli, 1998; Poli and Schmidt, 2002; Hacker et al., 2003; Hermann et al., 2006). Piston cylinder synthesis experiments in a model crustal composition at 2.0–4.5 GPa and 680–1150 °C doped with trace elements (REE) demonstrate that fluids form at the expense of zoisite at T > 700 °C and P = 2.0 GPa (Hermann, 2002a) according to the dehydration melting reaction: zoisite + Mgphase ? clinopyroxene + kyanite + allanite + liquid. The liquids produced are hydrous granitic melts at T > 800– 900 °C. Given that the REE concentration in allanite is much higher than that in zoisite, the doping of REE in this experiment is essential to the formation of allanite. The appearance of allanite in the Chizhuang quartz vein indicates that the UHP fluids have very high REE concentrations. Also, Varbec et al. (2006) suggested that the UHP fluids can be produced by dehydration melting of eclogitic zoisite. In the Alps, the kyanite–quartz band (or vein) has also been proposed to be a granitic melt, formed by the dehydration melting reaction: talc + kyanite = pyrope + coesite + liquid (Schreyer et al., 1987; Schertl et al., 1991; Sharp et al., 1993). The Chizhuang Ky–Qtz vein has a similar composition to the Alps kyanite–quartz band; therefore it is regarded to be products of the dehydration melting reaction.

In the Qinglongshan eclogites, epidote and zoisite occur as porphyroblast with inclusions of garnet and omphacite. Ferrando et al. (2005a) and Zhang et al. (2005d) suggested that the epidote and/or zoisite were formed during the UHP eclogite-facies retrograde stage, and are not primary peakUHP phases. Therefore, it is possible that the epidote in the Donghai eclogites contain inclusions of quartz pseudomorphs after coesite (Hirajima et al., 1990; Zhang, 1992; Zhang et al., 1995; Cong and Wang, 1996). This conclusion that epidote formed by retrogression should also be applied to the zoisite of the Chizhuang eclogite as both epidote and zoisite from these eclogite bodies have the same characteristics. We suggest that the epidote and zoisite were consumed by dehydration reactions as demonstrated by the experiment of Hermann (2002a), and then formed again by hydration during retrograde metamorphism of UHP eclogites as discussed in previous studies (Ferrando et al., 2005a; Zhang et al., 2005d). Talc is present in the Donghai eclogites but it is probably a retrograde phase since the peak metamorphic conditions reached and even exceeded the conditions required for the reaction of talc = enstatite + quartz + fluid (<800 °C at pressures >3.0 GPa) (Ferrando et al., 2005a). Thus, we suggest that the silicate-rich fluids attending peak-UHP metamorphism of the Sulu orogen were possibly derived from the breakdown of zoisite and talc during deep subduction of the continental crust.

Fluids in deeply subducted continent

8000

25000

Elements (ppm)

Elements (ppm)

30000 La Ce Nd

20000 15000 10000 5000

6000

Pr Sr

Th Sm

4000

2000

1mm 0

0 Zo

Al Aln

Zo Z

Zo

700

Aln

Zo

200

600

Zn Cr Co

160

Elements (ppm)

Elements (ppm)

3221

500 400 V U Eu Gd

300 200 100 0

Sc Y

Ni Ga Pb

120 80 40 0

Zo

Aln

Zo

Zo

Aln

Zo

Fig. 6. Compositional profile of the allanite and its zoisite rim (sample CZ20V). The analyzed profile location is shown in Fig. 3B.

8.2. Composition of the UHP metamorphic fluids Studies of fluid inclusions from eclogite-facies rocks can provide valuable information on the nature and composition of fluids present during HP and UHP metamorphism (Scambelluri and Philippot, 2001; Hermann, 2003; Touret and Frezzotti, 2003). Most investigations of fluid inclusions hosted in Dabie-Sulu UHP minerals have suggested that the high-salinity aqueous fluids with varying gas species (CO2, CH4 and N2) were present during the peak-UHP metamorphism (e.g., You et al., 1996; Shen et al., 1996, 2003a,b, 2005, 2006; Xiao et al., 2000, 2001; Fu et al., 2001, 2003; Fan et al., 2003; Zhang et al., 2005b, 2006a), and that the fluid inclusion types and compositions vary on scales ranging from regional to centimeter (e.g., Fu et al., 2001, 2003; Zhang et al., 2007). Hermann et al. (2006) pointed out that the observed variability in fluid inclusion populations is a function of localized fluid–rock interactions prior to or during their trapping. Hence, highly saline and solute-rich fluid inclusions may not represent original fluid compositions as they are likely residues of aqueous fluid–rock interactions or vein formation, where H2O preferentially partitions into hydrous minerals (Svensen et al., 1999; Scambelluri and Philippot, 2001) or a coexisting melt phase (Philippot, 1993; Philippot et al., 1995). Published data from theoretical phase relations, petrographic examinations of natural rocks, and experiments show that eclogite-facies prograde metamorphism at about 1.5–2.5 GPa and 500–600 °C represents a major dehydration event in subducted crust (Her-

mann et al., 2006); fluids produced in such an environment would be H2O-rich with a significant solute content. According to these considerations, we suggest that the H2O-dominated fluid inclusions in eclogitic garnet, omphacite and zircon were trapped during the prograde metamorphism from the amphibolite-facies to the quartz–eclogitefacies in the Dabie-Sulu orogen. As described in previous sections, the complex quartz veins in the Chizhuang eclogite were formed during the UHP metamorphic stages. Most vein minerals form very large euhedral to subhedral crystals (or megacrysts) and contain abundant primary fluid inclusions with multi-solid phases, indicating that veins were crystallized freely from a silicate-rich aqueous fluid or melt. Thus, we envisage that primary MS inclusions (type I) and multi-solid fluid inclusions (type II) trapped in kyanite, allanite and zoisite megacrysts may represent an original fluids attending UHP metamorphism. The analysis of vein systems can provide important constraints on fluid composition and circulation in metamorphic terranes because these veins were deposited from fluids or are frozen melts (e.g., Yardley and Bottrell, 1992; Ague, 1994a,b; Cesare, 1994; Oliver, 1996; Oliver and Bons, 2001; Molina et al., 2004). Veins that cut HP/UHP rocks clearly involve fluids in their formation and therefore have the potential to provide critical information on fluid compositions and fluid–rock interactions (Hermann et al., 2006). As mentioned above, oxygen isotope data show that the fluid flow was very limited during the UHP metamorphism of the Dabie-Sulu orogen. Therefore fluids generated possibly by breakdown

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Z.-M. Zhang et al. / Geochimica et Cosmochimica Acta 72 (2008) 3200–3228

Fig. 7. Microphotographs of fluid inclusions in the UHP veins. (A) multiphase solid (MS) inclusions occurring as a cluster within a kyanite (Ky) crystal in Aln–Qtz vein (sample CZ20V); one of the inclusions contains solid phases of paragonite (Pg), corundum (Crn), pyrite (Py), an unknown mineral (X) and a void (V). The upper-left insert is taken under an ordinary microscope and the lower-right insert is a back-scattered electronic image; (B) an isolated MS inclusion in kyanite crystal contains Pg, anhydrite (Anh), siderite (Sd), magnetite (Mag), H2O (L) and an unknown phase X (sample CZ20V); (C) a zoned allanite (Aln) crystal in Aln–Qtz vein (sample CZ18V); the core of the crystal contains abundant and parallel distributed multi-solid fluid inclusions shown in the magnified inset in the low-right, whereas the rim of the crystal is inclusion-free; (D) a part of an allanite megacryst containing multi-solid fluid inclusions with daughter phases of Anh, Cal, Pg and celestite (Cls) as well as liquid (L) and vapor (V) water phases. The inclusions occur as clusters or intragranular trails (the upper-left insert) oriented parallel to the c-axis of the host mineral. Note that the inclusion trails do not cut across allanite grain boundary (sample CZ26V); (E) an isolated multi-solid fluid inclusion lying along the c-axis of zoisite (Zo), and containing daughter minerals of Ms, Cal, Anh and two unknown solids (X, Y) in addition to liquid (L) and vapor (V) water phases (sample CZ26V); (F) multi-solid fluid inclusions occurring as intragranular trails in Zo, and containing Ms, Cal, Anh, an opaque (Op) as well as water (L and V) phases (sample CZ26V). All images were taken under plain light.

of zoisite and talc almost completely remained within the host eclogite, and the composition of the bulk vein + trapped abundant multi-solid fluid inclusions probably equals that of the UHP fluids.

Based on these considerations and the detailed petrological and chemical data of the vein minerals, the geochemical characteristics of fluids attending the peak-UHP metamorphism of the Sulu orogen can be summarized as follows: (1)

Fluids in deeply subducted continent

They contain significant amounts of H2O since hydrous allanite and/or zoisite are the major minerals of the veins, and abundant primary aqueous inclusions were trapped in vein minerals. Based on the phase ratios of type II fluid inclusions distributed widely in vein minerals, the minimum H2O content of the original UHP fluids is estimated to be ca. 30 vol% because the volume of H2O liquid and gas phases in type II inclusions ranges from 30 to 70 vol%. (2) The UHP fluids are rich in SiO2, Al2O3 and CaO with varying amounts of MgO, FeO and Na2O plus CO2 and SO4 as evidenced by the vein mineral assemblage of quartz + allanite (or zoisite) + kyanite with minor omphacite and garnet, as well as daughter mineral associations in the multi-solid fluid inclusions. (3) These fluids are characterized by very high REE contents. The main phase allanite of veins contains up to 5.4–7.1 wt% of LREE, and zoisite and apatite are also enriched in REE. In addition, celestite and apatite, which favor REEs, were found as the daughter minerals in abundant type II inclusions. This also shows that the UHP fluids were highly enriched in REE and that the REE-rich allanite and apatite of the vein can be crystallized directly from the fluids. (4) These fluids have relatively high HFSE, and Sr, Ba, V and Pb contents. Abundant rutile in veins is an important host for HFSE and V, whereas allanite is rich in Sr, Ba, Pb, V, Th and U, and zoisite and epidote also have relatively high Sr and Ba contents. Hence, we suggest that UHP fluids comprise mainly SiO2 + Al2O3 + CaO + MgO + FeO + Na2O + H2O as well as being enriched in LREE, HFSE and P, V, Sr, Ba and Pb. These facts demonstrate that the UHP fluids in the Chizhuang eclogite are rich in silica, and do not belong to a simple aqueous system with variable salinity and gas species. Ferrando et al. (2005b) described some primary MS inclusions in eclogitic minerals from Qinglongshan, and proposed that they represent remnants of high-density supercritical silicate-rich aqueous fluids that were in equilibrium with peak minerals at UHP conditions. These fluids have very complex silicate components, contain 7– 18 wt% H2O, show characteristics transitional between aqueous fluids and silicate melts, and were probably produced by dehydration reactions of host rocks during the latest stages of subduction. Shen et al. (2005) and Zhang et al. (2007) have also reported some primary multiphase fluid inclusions in UHP eclogitic omphacite from the CCSD main hole. Their compositions are constrained in the system of NaCl–CaCl2–CO2–SiO2–H2O with possibly some Fe and Mg, and therefore the fluids show characteristics of supercritical fluids. These conclusions are consistent with this study and previous results. For example, Schneider and Eggler (1986) and Becker et al. (1999) concluded that hydrous fluids derived from dehydration of metabasalts may contain SiO2 and Al2O3 as major solute components; Manning (2004) argued that fluids in subduction zones have properties intermediate between hydrous silicate liquid and H2O. Hermann et al. (2006) suggested that fluids attending the UHP metamorphism of the Dabie orogen belong to a hydrous melt (H2O < 35 wt%). The present study has not only confirmed that peak-stage fluids of the Sulu UHP metamor-

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phism are supercritical silicate-rich aqueous fluids, but also provides important constraints on the geochemical characteristics of fluids in the deeply subducted crust. 8.3. Geodynamic implications Trace element analysis of minerals from HP to UHP rocks suggest that lawsonite and epidote/zoisite are the main minerals containing LREE in rocks of metabasic and metapelitic compositions (Domanik et al., 1993; Tribuzio et al., 1996). The stability of lawsonite and clinozoisite/ zoisite in rocks of such compositions has been experimentally investigated (Poli and Schmidt, 1995; Okamoto and Maruyama, 1999; Hermann, 2002a); clinozoisite/zoisite is not stable at P > 3.0 GPa, whereas lawsonite stability is restricted to lower temperatures (<650 °C at 3.0 GPa; <750 °C at 5.5 GPa). Trace element distributions from natural rocks and experimental results indicate that the breakdown of hydrous phases such as lawsonite and zoisite will produce LREE-rich fluids. The present study demonstrates that the UHP fluids trapped in the Chizhuang eclogite are not only enriched in LREE, but also have high concentrations of LILE as well as HFSE. Thus, we suggest that some of the LILE and HFSE hosted in eclogitic phengite, omphacite and rutile must have been dissolved in the UHP fluids derived mainly from the breakdown of the eclogitic zoisite. Recent studies have shown that both mobile and supposedly immobile elements have higher solubility in fluids from deep subduction zones under the UHP metamorphic conditions (e.g., Manning, 2004; Hermann et al., 2006). Abundant primary multi-solid fluid inclusions trapped within the Chizhuang UHP vein minerals contain highly oxidized daughter minerals, e.g., anhydrite and magnetite consistent with previous observations in quartz veins, which indicates high oxygen fugacity in fluids released during subduction (Sun et al., 2007), and provides a plausible explanation for the oxidized nature of arc magmas (Ballhaus, 1993; Brandon and Draper, 1996; Parkinson and Arculus, 1999; Mungall, 2002). Niobium, Ta and other HFSE are widely used as geochemical indicators of geological processes and in global earth models. In particular, the depletion of Nb and Ta relative to LREE and other highly incompatible elements is a distinct feature of the continental crust and island-arc basalts, which is not observed in common mid-ocean ridge basalts (MORB) and oceanic island basalts (e.g., Hofmann, 1988; Rudnick et al., 2000). Niobium and Ta are refractory and lithophile elements and exhibit similar geochemical behaviors during magmatism; hence the Nb/Ta ratio of the bulk silicate earth should be similar to the chondritic value of 17.5 ± 0.6 (Jochum and Stolz, 1997; Rudnick et al., 2000). Recent studies have shown that two global terrestrial reservoirs, the continental crust and the depleted mantle (DM, source of MORB) have subchondritic Nb/ Ta values of 12 (Barth et al., 2000) and 15.5, respectively (Jochum and Hofmann, 1998). This finding has given a new impetus to the search for a ‘‘hidden” suprachondritic reservoir capable of balancing the subchondritic reservoirs (Rudnick et al., 2000).

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Rutile is a common minor phase in HP and UHP rocks, especially in eclogites (e.g., Liou et al., 1998; Zack et al., 2002), and acts as a controller of strongly influences Nb and Ta budgets and Nb/Ta fractionation in subduction-zone processes (e.g., Green, 1995; Stalder et al., 1998; Foley et al., 2000; Rudnick et al., 2000; Klemme et al., 2002). The rutile/melt partitioning results from previous studies confirm that rutile is a dominant carrier for Nb and Ta, and that rutile favors Ta over Nb with DNb consistently lower than DTa for each rutile/melt pair (Green and Pearson, 1986; Jenner et al., 1993; Foley et al., 2000; Schmidt et al., 2004; Xiong et al., 2005). Rutile is a necessary residual phase during the generation of Archean tonalite–trondhjemite–granodiorite (TTG) magmas to account for the negative Nb–Ta anomaly of the magmas. The depths for TTG production via melting of subducted oceanic crust must be greater than 45–50 km based on the minimum pressure of 1.5 GPa for rutile appearance in rocks of mafic composition. Rutile fractionates Nb from Ta, resulting in slightly higher Nb/Ta in coexisting melts. The Archean TTG magmas with subchondritic Nb/Ta must, therefore, have been derived from low Nb/Ta source regions unless alternative magmatic processes have lowered the Nb/Ta values (e.g., Rapp et al., 2003; Xiong et al., 2005). Also rutile-bearing residues should display lower Nb/Ta after TTG liquids are extracted. Hence, available data do not support the suggestion that subducted rutile-bearing eclogitic oceanic crust is a suprachondritic Nb/Ta reservoir on the Earth (e.g., Xiong et al., 2005). However, the present study demonstrates that rutile crystals in UHP veins have lower Nb/Ta ratios than those of host eclogitic rutile. More importantly, vein rutile grains have subchondritic Nb/Ta values (ranging from 6.2 to 17.4, with an average of 12.1) whereas the eclogitic rutile crystals have suprachondritic Nb/Ta values (ranging from 21.9 to 36.4). Moreover, our study shows that the rutile crystals of UHP eclogites, including 16 samples of depths between 100 and 2000 m from the CCSD main hole drilled into the Maobei body, also have high and suprachondritic Nb/Ta values (with a mean value of 21.0). In contrast, 128 spot analyses in coarsegrained rutile grains (up to 6–8 mm in size) of hydrous eclogites and UHP quartz veins hosted in the same Maobei body have Nb/Ta values with an average value of 10.5 similar to the subchondritic value, except for the very narrow inner rims with Nb/Ta value similar to the chondritic value (Xiao et al., 2006a). Based on these observations, we suggest that the Nb and Ta have different solubility in UHP fluids, and that their selective mobility has resulted in significant fractionation of Nb and Ta in the deeply subducted continental crust and the residual eclogites have an elevated and suprachondritic Na/Ta values, whereas UHP fluids released from host eclogites have lower and subchondritic Nb/Ta values. Recent studies have already shown that voluminous UHP eclogites have been subducted to >80 to 100 km depth of the upper mantle in the Dabie-Sulu orogen (e.g., Xu et al., 1992; Zhang et al., 1994, 1995; Liou et al., 2000; Zhang et al., 2006c). Therefore, we speculate that the

huge volume of eclogites with high Nb/Ta values may be the complementary hidden suprachondritic reservoir capable of balancing the subchondritic reservoirs. 9. CONCLUSIONS (1) The complex veins hosted in the Sulu eclogites contain variable mineral associations, including the following UHP mineral assemblages: coesite + allanite + kyanite + omphacite + rutile + apatite, coesite + zoisite + omphacite + rutile, coesite + jadeite + kyanite + allanite (or epidote) + garnet + phengite, and coesite + zoisite + rutile. They were crystallized directly from the silicate-rich fluids formed probably by dehydration of eclogitic zoisite and talc when the continental crust subducted to upper mantle depth of >100 km. (2) The chemical compositions of the UHP vein minerals and the primary solid and fluid inclusions trapped by these vein minerals indicate that the fluids in the deeply subducted continental crust were silicate-rich supercritical fluids with very high REE, as well as LILE, HFSE and TME, and that many normally fluid-immobile elements were mobilized during interactions between supercritical fluids and host rocks (minerals) under the extreme UHP metamorphic conditions. (3) Abundant primary multi-solid fluid inclusions trapped within UHP vein minerals contain highly oxidized daughter minerals of anhydrite and magnetite. This indicates the high oxygen fugacity in subduction released fluids, and provides a feasible interpretation to the fluids released during subduction were oxidizing. (4) The supercritical fluids have resulted in major fractionation between Nb and Ta; the residual eclogites after extraction of the fluids have higher Nb/Ta value than that of the chondrite, and may be the suprachondritic reservoir capable of balancing the subchondritic reservoirs.

ACKNOWLEDGMENTS This work is supported by the Major State Basic Research Development Program (2003CB716501) and the National Natural Science Foundation of China (40399142 and 40472036). This paper also represents one of the research products for a Sino-American cooperative project supported by NSF EAR 0003355 and 0506901. The manuscript has been critically reviewed and materially improved by Dr. Sarah Penniston-Dorland, Dr. Sorena Sorensen, and also corrected and edited by the Associate Editor Dr. Thomas Chacko. The English of this revised version has been materially improved by Dr. Thomas Chacko and Prof. Bob Zartman. We thank the above named institutes and scientists for their support and help.

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