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Article: Low-T eclogite in the Dabie terrane of China: Petrological and isotopic constraints on fluid activity and radiometric dating

TitleLow-T eclogite in the Dabie terrane of China: Petrological and isotopic constraints on fluid activity and radiometric dating
Authors
Issue Date2004
PublisherSpringer Verlag. The Journal's web site is located at http://link.springer.de/link/service/journals/00410/index.htm
Citation
Contributions To Mineralogy And Petrology, 2004, v. 148 n. 4, p. 443-470 How to Cite?
AbstractWhile extensive studies have demonstrated fluid release during subduction of oceanic crust, little attention has been paid to fluid activity during subduction and exhumation of continental crust. Abundant occurrence of quartz veins within eclogites in the Dabie-Sulu orogenic belt of China provides us with an opportunity to study the origin and role of vein-forming fluids with respect to heat and mass transfer during ultrahigh pressure (UHP) metamorphism and its relevant processes. This study focuses on kyanite-quartz vein that occurs as polycrystalline aggregates within the low-T eclogite in the Dabie terrane, which are interpreted as pseudomorphs after former porphyroblasts of lawsonite. Coesite pseudomorphs were found for the first time in eclogite garnet, resulting in a revised estimate of peak P-T conditions at 670°C and 3.3 GPa for the eclogite and thus upgrading the high-P unit to an UHP unit. On the basis of the relationship between calculated P-T path and metamorphic reactions as well as the absence of foliation texture, and undulose extinction of quartzes in the vein, we conclude that lawsonite breakdown into kyanite-quartz-zoisite assemblage took place at the onset of exhumation subsequent to peak pressure. Retrograde metamorphism caused O and H isotope disequilibria between some of the minerals, but the fluid for retrograde reactions was internally buffered in stable isotope compositions. Zircon U-Pb dating and whole-rock Nd-Sr isotope analyses indicate that eclogite protolith is the paleoceanic basalt that was derived from the depleted mantle by magmatism at about 1.8 to 1.9 Ga but experienced hydrothermal alteration by surface waters. The altered basalt underwent UHP metamorphism in the Triassic that caused fluid release for zircon growth/overgrowth not only at about 242±3 Ma prior to the onset of peak pressure but also at about 222±4 Ma during decompression dehydration by lawsonite breakdown and hydroxyl exsolution in the low-T/UHP eclogite. Consistent ages of 236.1±4.2 Ma and 230±7 Ma were obtained from mineral Sm-Nd and Rb-Sr isochron dating, respectively, indicating attainment and preservation of Nd and Sr isotope equilibria during the Triassic UHP eclogite-facies metamorphism. Ar-Ar dating on paragonite from the eclogite gave consistent plateau and isochron ages of 241.3±3.1 Ma and 245.5±9.8 Ma, respectively, which are interpreted to date paragonite crystallization during the prograde eclogite-facies metamorphism. The timing of peak UHP metamorphism for the low-T eclogite is constrained at sometime prior to 236.1±4.2 Ma. Thus the termination age of peak UHP metamorphism may be different in different slices of deep-subducted slab. © Springer-Verlag 2004.
Persistent Identifierhttp://hdl.handle.net/10722/91303
ISSN
2015 Impact Factor: 3.218
2015 SCImago Journal Rankings: 2.582
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorLi, XPen_HK
dc.contributor.authorZheng, YFen_HK
dc.contributor.authorWu, YBen_HK
dc.contributor.authorChen, Fen_HK
dc.contributor.authorGong, Ben_HK
dc.contributor.authorLi, YLen_HK
dc.date.accessioned2010-09-17T10:16:38Z-
dc.date.available2010-09-17T10:16:38Z-
dc.date.issued2004en_HK
dc.identifier.citationContributions To Mineralogy And Petrology, 2004, v. 148 n. 4, p. 443-470en_HK
dc.identifier.issn0010-7999en_HK
dc.identifier.urihttp://hdl.handle.net/10722/91303-
dc.description.abstractWhile extensive studies have demonstrated fluid release during subduction of oceanic crust, little attention has been paid to fluid activity during subduction and exhumation of continental crust. Abundant occurrence of quartz veins within eclogites in the Dabie-Sulu orogenic belt of China provides us with an opportunity to study the origin and role of vein-forming fluids with respect to heat and mass transfer during ultrahigh pressure (UHP) metamorphism and its relevant processes. This study focuses on kyanite-quartz vein that occurs as polycrystalline aggregates within the low-T eclogite in the Dabie terrane, which are interpreted as pseudomorphs after former porphyroblasts of lawsonite. Coesite pseudomorphs were found for the first time in eclogite garnet, resulting in a revised estimate of peak P-T conditions at 670°C and 3.3 GPa for the eclogite and thus upgrading the high-P unit to an UHP unit. On the basis of the relationship between calculated P-T path and metamorphic reactions as well as the absence of foliation texture, and undulose extinction of quartzes in the vein, we conclude that lawsonite breakdown into kyanite-quartz-zoisite assemblage took place at the onset of exhumation subsequent to peak pressure. Retrograde metamorphism caused O and H isotope disequilibria between some of the minerals, but the fluid for retrograde reactions was internally buffered in stable isotope compositions. Zircon U-Pb dating and whole-rock Nd-Sr isotope analyses indicate that eclogite protolith is the paleoceanic basalt that was derived from the depleted mantle by magmatism at about 1.8 to 1.9 Ga but experienced hydrothermal alteration by surface waters. The altered basalt underwent UHP metamorphism in the Triassic that caused fluid release for zircon growth/overgrowth not only at about 242±3 Ma prior to the onset of peak pressure but also at about 222±4 Ma during decompression dehydration by lawsonite breakdown and hydroxyl exsolution in the low-T/UHP eclogite. Consistent ages of 236.1±4.2 Ma and 230±7 Ma were obtained from mineral Sm-Nd and Rb-Sr isochron dating, respectively, indicating attainment and preservation of Nd and Sr isotope equilibria during the Triassic UHP eclogite-facies metamorphism. Ar-Ar dating on paragonite from the eclogite gave consistent plateau and isochron ages of 241.3±3.1 Ma and 245.5±9.8 Ma, respectively, which are interpreted to date paragonite crystallization during the prograde eclogite-facies metamorphism. The timing of peak UHP metamorphism for the low-T eclogite is constrained at sometime prior to 236.1±4.2 Ma. Thus the termination age of peak UHP metamorphism may be different in different slices of deep-subducted slab. © Springer-Verlag 2004.en_HK
dc.languageengen_HK
dc.publisherSpringer Verlag. The Journal's web site is located at http://link.springer.de/link/service/journals/00410/index.htmen_HK
dc.relation.ispartofContributions to Mineralogy and Petrologyen_HK
dc.titleLow-T eclogite in the Dabie terrane of China: Petrological and isotopic constraints on fluid activity and radiometric datingen_HK
dc.typeArticleen_HK
dc.identifier.emailLi, YL:yiliang@hkucc.hku.hken_HK
dc.identifier.authorityLi, YL=rp01354en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1007/s00410-004-0616-9en_HK
dc.identifier.scopuseid_2-s2.0-10644245813en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-10644245813&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume148en_HK
dc.identifier.issue4en_HK
dc.identifier.spage443en_HK
dc.identifier.epage470en_HK
dc.identifier.isiWOS:000225608400004-
dc.publisher.placeGermanyen_HK
dc.identifier.scopusauthoridLi, XP=8553095200en_HK
dc.identifier.scopusauthoridZheng, YF=7404838286en_HK
dc.identifier.scopusauthoridWu, YB=8733547800en_HK
dc.identifier.scopusauthoridChen, F=7404907137en_HK
dc.identifier.scopusauthoridGong, B=7102144191en_HK
dc.identifier.scopusauthoridLi, YL=27171876700en_HK
dc.identifier.citeulike683841-

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