In this study,a tremolite marble from the Dabie ultrahigh-pressure(UHP)terrane,eastcentral China was investigated for its metamorphic evolution by focusing on zircon.The marble contains an amphibolite-facies assemblag...In this study,a tremolite marble from the Dabie ultrahigh-pressure(UHP)terrane,eastcentral China was investigated for its metamorphic evolution by focusing on zircon.The 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 conditions.Cathodoluminescence reveals eight characteristic zones for zircon.As indicated by mineral inclusions in zircon,two zones formed no earlier than amphibolite-facies retrogression and are too thin to date.The 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 conditions.Phase equilibria calculations illustrat that the Na-richest diopside formed under UHP conditions.Being 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 Mn-endmembers.The 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 zones.Statistically,the eclogite-facies ages are characterized by a Gaussian distribution with a median peak at 232 Ma.We propose that zircon experienced a“protracted”recrystallization and/or growth history in the tremolite marble during the Triassic subduction and exhumation.展开更多
基金supported by a grant from the Natural Science Foundation of China (No.41972051)the Fundamental Research Funds for the Central Universities,China University of Geosciences (Wuhan)(No.CUG190627)
文摘In this study,a tremolite marble from the Dabie ultrahigh-pressure(UHP)terrane,eastcentral China was investigated for its metamorphic evolution by focusing on zircon.The 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 conditions.Cathodoluminescence reveals eight characteristic zones for zircon.As indicated by mineral inclusions in zircon,two zones formed no earlier than amphibolite-facies retrogression and are too thin to date.The 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 conditions.Phase equilibria calculations illustrat that the Na-richest diopside formed under UHP conditions.Being 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 Mn-endmembers.The 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 zones.Statistically,the eclogite-facies ages are characterized by a Gaussian distribution with a median peak at 232 Ma.We propose that zircon experienced a“protracted”recrystallization and/or growth history in the tremolite marble during the Triassic subduction and exhumation.
