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

Zhang, Zeming; Shen, Kun; Sun, Weidong; Liu, Yongsheng; Liou, J. G.; Cao, Sanjie; Wang, Jinli

doi:10.1016/j.gca.2008.04.014

Cited by 159 publications

(130 citation statements)

References 107 publications

(161 reference statements)

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“…Studies on the composition of fluid inclusions in the Sulu eclogites have shown that salt-bearing fluid inclusions formed under UHP conditions are dominantly of NaClCaCl 2 -H 2 O [19,[21][22][23]. Such compositions are substantially deviated from KCl-NaCl of solid salt within the quartzofeldspathic inclusion reported in this study, implying different formation mechanisms.…”

Section: Discussionmentioning

confidence: 60%

“…High salinity fluid inclusions have been reported in garnet as well as omphacite in UHP rocks. Fluid inclusions hosted by UHP minerals in the Dabie-Sulu orogenic belt consist mainly of H 2 OCO 2 , and intermediate to low salinity H 2 O-CO 2 fluids were presented at prograde, peak, and retrograde metamorphic stages [19][20][21][22][23]. Furthermore, high salinity fluids of NaCl-CaCl 2 -H 2 O composition also existed at least locally under UHP conditions [19,[21][22][23].…”

mentioning

confidence: 99%

“…Fluid inclusions hosted by UHP minerals in the Dabie-Sulu orogenic belt consist mainly of H 2 OCO 2 , and intermediate to low salinity H 2 O-CO 2 fluids were presented at prograde, peak, and retrograde metamorphic stages [19][20][21][22][23]. Furthermore, high salinity fluids of NaCl-CaCl 2 -H 2 O composition also existed at least locally under UHP conditions [19,[21][22][23]. Factors that control the chemical composition and salinity of such fluid inclusions include their sources as well as the hosted mineral-fluid re-equilibration [3,24].…”

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confidence: 99%

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Metamorphic solid salt (KCl-NaCl) in quartzo-feldspathic polyphase inclusions in the Sulu ultrahigh-pressure eclogite

Zeng

Chen

2012

Chin. Sci. Bull.

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Unusual polyphase inclusions of K-feldspar + quartz + titanite + solid salt and K-feldspar + albite + quartz + epidote with textures similar to the other K-feldspar + quartz inclusions were found in omphacite grains from the Sulu ultrahigh pressure (UHP) eclogites. One of these inclusions contain square to round solid salt inclusions of KCl-NaCl composition. Such a mineral assemblage within K-feldspar-bearing inclusions hosted by UHP metamorphic phases suggests that (1) potassium granitic melts enriched in Cl components were presented during UHP metamorphism or at the early stage of rapid exhumation of deeply subducted continental slab; (2) they were resulted from reactions between the incoming granitic melts and quartz (or coesite); and (3) solid salt inclusions of NaCl-KCl were derived from dehydration and desiccation of Cl-bearing melts. Our new observations further demonstrate that during the tectonic evolution of UHP rocks, fertile components within deeply subducted continental materials could undergo partial melting, leading to the formation of Cl-bearing potassium granitic melts and substantial migration of fluid-conservative elements (e.g. Ti, Hf) within the UHP slab. [17,18]. Such fluids, geochemically similar to granitic melts, could dissolve not only a large quantity of large lithophile elements (LILE) and rare earth elements (REE), but also normally fluid-immobile elements such as high field strength elements (HFSE), and become an excellent medium to transport these elements. During the tectonic evolution of continental subduction zones, formation and migration of granitic melts or supercritical fluids not only affect the geochemical properties of the subducted continental slab itself, but also exert strong influences on the physical and chemical properties of the overlying slab. Therefore, identification whether the deeply subducted continental material experienced partial melting and whether supercritical fluids presented is one of the frontiers of recent UHP studies [16].Resolving these issues will promote our understanding and appreciation of the pronounced physical and chemical effects of deep subduction and associated UHP metamorphic reactions of continental materials. The geochemical nature of fluids associated with UHP metamorphism is commonly inferred from fluid inclusions in UHP phases. High salinity fluid inclusions have been

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Section: Discussionmentioning

confidence: 60%

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confidence: 99%

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confidence: 99%

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Metamorphic solid salt (KCl-NaCl) in quartzo-feldspathic polyphase inclusions in the Sulu ultrahigh-pressure eclogite

Zeng

Chen

2012

Chin. Sci. Bull.

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“…It is not clear when anhydrite formed from the supercritical fluid, but the formation should be under relatively high -P and high -T conditions. In addition to these examples, there are several reports on occurrences of sul- phates in HP or UHP metamorphic rocks (e.g., Philippot and Selverstone, 1991;Zhang et al, 2008). Thus, these sulphates can be stable even under high -P conditions.…”

Section: Discussionmentioning

confidence: 98%

Sr-sulphate and associated minerals found from kyanite-bearing eclogite in the Moldanubian Zone of the Bohemian Massif, Czech Republic

Nakamura

Kobayashi

Shimobayashi

et al. 2010

Journal of Mineralogical and Petrological Sciences

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Sr -sulphate, celestine, was newly found in a kyanite -bearing eclogite associated with the Nové Dvory peridotite mass in the Moldanubian Zone of the Bohemian Massif, Czech Republic. Celestine is closely associated with anhydrite, pyrite, pyrrhotite and chalcopyrite, and those minerals occur in the matrix, where fine -grained omphacite aggregate and kelyphites after garnet develop. A common Sr reservoir in eclogite is known to be epidote, but the maximum pressure -temperature (P -T) conditions of the studied eclogite was estimated as about 1050 -1150 °C, 4.5 -4.9 GPa. In such extremely high P -T conditions, epidote should be unstable. In fact, epidote is absent from most of eclogites in the Moldanubian Zone of Czech Republic. These facts suggest that a Sr -reservoir after the epidote -breakdown in subducting eclogite might be celestine, or its high -P polymorph, although the formation stage of celestine in the study sample and maximum stability limits of celestine are not known. Another idea is that celestine in the study sample was formed at relatively shallow levels after the ascent of the eclogite. In this case, omphacite and apatite would have contained significant amount of Sr under the eclogitefacies conditions. Otherwise, metasomatic infiltration of Sr -rich fluids into the eclogite is necessary for the formation of celestine in order to provide sufficient amount of Sr. A Ba -rich alumino -silicate, probably celsian, was also found as a retrograde product around pyrrhotite in kelyphite and in symplectites mainly composed of augite and plagioclase after omphacite. Several grains of biotite are also present along the margin of garnet and in the symplectites after omphacite. In addition, small amounts of muscovite and amphibole are present in the symplectites after omphacite. These findings suggest that metasomatism with Sr -and Ba -rich fluids may have occurred during decompression of the eclogite and may not be indicative of the UHP history of these rocks.

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“…The overall thickness of eclogites is about 1,200 m. A garnet peridotite sequence, which is sandwiched by normal or quartz-rich eclogite at the base and highly Fe-Tienriched eclogite at the top, has been recovered from 603.2 to 683.5 m ). High-pressure veins with eclogite-facies mineral assemblages and retrograde veins with amphibolite-facies mineral assemblages are commonly observed in the eclogite cores (e.g., Xu 2007;Zhang et al 2008). All rock types down to 5,158 m from the CCSD have been subjected to UHP metamorphism, as documented by the preservation of coesite inclusions in zircon .…”

Section: Geological Background and Samplesmentioning

confidence: 99%

Fluid/rock interaction and mass transfer in continental subduction zones: constraints from trace elements and isotopes (Li, B, O, Sr, Nd, Pb) in UHP rocks from the Chinese Continental Scientific Drilling Program, Sulu, East China

Xiao

Hoefs²,

Hou

et al. 2011

Contrib Mineral Petrol

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In order to better understand the role of fluids during subduction and subsequent exhumation, we have investigated whole-rock and mineral chemistry (major and trace elements) and Li, B as well as O, Sr, Nd, Pb isotopes on selected continuous drill-core profiles through contrasting lithological boundaries from the Chinese Continental Scientific Drilling Program (CCSD) in Sulu, China. Four carefully selected sample sets have been chosen to investigate geochemical changes as a result of fluid mobilization during dehydration, peak metamorphism, and exhumation of deeply subducted continental crust. Our data reveal that while O and Sr-Nd-Pb isotopic compositions remain more or less unchanged, significant Li and/or B isotope fractionations occur between different lithologies that are in close contact during various metamorphic stages. Samples that are supposed to represent prograde dehydration as indicated by veins formed at high pressures (HP) are characterized by element patterns of highly fluid-mobile elements in the veins that are complementary to those of the host eclogite. A second sample set represents a UHP metamorphic crustal eclogite that is separated from a garnet peridotite by a thin transitional interface. Garnet peridotite and eclogite are characterized by a [10% difference in MgO, which, together with the presence of abundant hydroxyl-bearing minerals and compositionally different clinopyroxene grains demonstrate that both rocks have been derived from different sources that have been tectonically juxtaposed during subduction, and that hydrous silicate-rich fluids have been added from the subducting slab to the mantle. Two additional sample sets, comprising retrograde amphibolite and relatively fresh eclogite, demonstrate that besides external fluids, internal fluids can be responsible for the formation of amphibolite. Li and B concentrations and isotopic compositions point to losses and isotopic fractionation during progressive dehydration. On the other hand, fluids with isotopically heavier Li and B are added during retrogression. On a small scale, mantle-derived rocks may be significantly metasomatized by fluids derived from the subducted slab. Our study indicates that during high-grade metamorphism, Li and B may show different patterns of enrichment and of isotopic fractionation.

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

Cited by 159 publications

References 107 publications

Metamorphic solid salt (KCl-NaCl) in quartzo-feldspathic polyphase inclusions in the Sulu ultrahigh-pressure eclogite

Metamorphic solid salt (KCl-NaCl) in quartzo-feldspathic polyphase inclusions in the Sulu ultrahigh-pressure eclogite

Sr-sulphate and associated minerals found from kyanite-bearing eclogite in the Moldanubian Zone of the Bohemian Massif, Czech Republic

Fluid/rock interaction and mass transfer in continental subduction zones: constraints from trace elements and isotopes (Li, B, O, Sr, Nd, Pb) in UHP rocks from the Chinese Continental Scientific Drilling Program, Sulu, East China

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