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zoned zircon from Eclogite Lenses in Marbles from the Dabie-Sulu UHP Terrane,China: A Clear Record of Ultra-deep Subduction and Fast Exhumation

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Acta Geologica Sinica(English Edition) 2007年第2期81卷 204-225页

作者： LIU Fulai A. GERDES P. T. ROBINSON XUE Huaimin YE Jianguo The Key Laboratory of Continental Dynamics Ministry of Land and Mineral Resources of China Institute of Geosciences Mineralogy J. W. Goethe University Frankfurt 60054 Germany Department of Earth Sciences Dalhousie University Halifax Nova Scotia Canada

Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure （UHP） terrane are deeply subducted meta-sedimentary rocks. zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphism during subduction, and later retrograde metamorphism during exhumation. Inherited （detrital） and metamorphic zircons were distinguished on the basis of transmitted light microscopy, cathodoluminescence （CL） imaging, trace element contents and mineral inclusions. The distribution of mineral inclusions combined with CL imaging of the metamorphic zircon make it possible to relate zircon zones （domains） to different metamorphic stages. Domain 1 consists of rounded, oblong and spindly cores with dark-luminescent images, and contains quartz eclogite facies mineral inclusion assemblages, indicating formation under high-pressure （HP） metamorphic conditions of T = 571-668℃ and P =1.7-2.02 GPa. Domain 2 always surrounds domain 1 or occurs as rounded and spindly cores with white-luminescent images. It contains coesite eclogite facies mineral inclusion assemblages, indicating formation under UHP metamorphic conditions of T = 782-849℃ and P 〉 5.5 GPa. Domain 3, with gray-luminescent images, always surrounds domain 2 and occurs as the outermost zircon rim. It is characterized by low-pressure mineral inclusion assemblages, which are related to regional amphibolite facies retrograde metamorphism of T = 600- 710℃ and P = 0.7-1.2 GPa. The three metamorphic zircon domains have distinct ages; sample H1 from the Dabie terrane yielded SHRIMP ages of 245 ± 4 Ma for domain 1, 235 ± 3 Ma for domain 2 and 215± 6 Ma for domain 3, whereas sample H2 from the Sulu terrane yielded similar ages of 244 ± 4 Ma, 233 ± 4 Ma and 214 ± 5 Ma for Domains 1, 2 and 3, respectively. The mean ages of these zones suggest that subduction to UHP depths took place over 10-11 Ma and exhumation of the rocks occurred over a period of 19-20 Ma. Thus, subduction from - 55 km to 〉 160 km deep mantle depth

关键词： zoned zircon SHRIMP U-Pb dating ultra-deep subduction fast exhumation eclogite lenses in marble Dabie-Sulu UHP belt

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Metamorphic Evolution of a Tremolite Marble from the Dabie UHP Terrane,China:A Focus on zircon

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Journal of Earth Science 2022年第2期33卷 493-506页

作者： Penglei Liu Zhenmin Jin School of Earth Sciences China University of GeosciencesWuhan 430074China

In this study,a tremolite marble from the Dabie ultrahigh-pressure(UHP)terrane,eastcentral China was investigated for its metamorphic evolution by focusing on *** marble contains an amphibolite-facies assemblage of dolomite,Mg-calcite,tremolite,biotite,and plagioclase,while zircon in the marble witnesses a complex recrystallization and growth history under both amphiboliteand eclogite-facies *** reveals eight characteristic zones for *** indicated by mineral inclusions in zircon,two zones formed no earlier than amphibolite-facies retrogression and are too thin to *** other six zones contain inclusions of dolomite,aragonite,diopside(X_(Na)=Na/(Na+Ca)=0.11-0.14),garnet(X_(Ca)=0.51-0.62,X_(Mg)=0.21-0.23,X_(Fe)=0.17-0.26,X_(Mn)=0.01),phengite and rutile,and formed under eclogite-facies *** equilibria calculations illustrat that the Na-richest diopside formed under UHP *** an accessory eclogite-facies mineral in the marble,the analyzed chemistry of garnet inclusions cannot be reproduced by phase equilibria calculations because solid-solution models for many other minerals don't incorporate *** eclogite-facies zircon zones show low HREE contents and flat MREE-HREE distribution patterns,which are interpreted to have been determined by the low bulk-rock HREE content instead of the presence of accessary garnet in the marble.U-Pb dating yielded a large age dataset ranging from about 250 to 210 Ma for the eclogite-facies zircon ***,the eclogite-facies ages are characterized by a Gaussian distribution with a median peak at 232 *** propose that zircon experienced a“protracted”recrystallization and/or growth history in the tremolite marble during the Triassic subduction and exhumation.

关键词： Dabie UHP marble mineral inclusion recrystallization zoned zircon tectonics

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