Monazite recorded Paleoproterozoic granulite-facies metamorphism and Triassic fluid modification of the Weihai pelitic granulite,Sulu orogen  

作　　者：Zhiwu XIONG Haijin XU Pan WANG Junfeng ZHANG 

机构地区：[1]School of Earth Sciences,China University of Geosciences,Wuhan,430074,China

出　　处：《Science China Earth Sciences》2021年第6期932-950,共19页中国科学（地球科学英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.42072058,41772054,41572039)。

摘　　要：Monazite is an important accessory mineral in the pelitic granulites(Weihai area,Sulu orogen),and is also a powerful monitor for understanding the metamorphic evolution of the granulites.The pelitic granulites incongruously occur as lenses in granitic gneisses.The lithologies of the lenses gradually change from core to margin:The undeformed coarse-grained granulite,the foliated fine-grained granulite,the garnet-biotite-gneiss,and the migmatized granulite.The lens cores mostly preserve a peak granulite-facies metamorphic mineral assemblage of garnet+plagioclase(antiperthite)+quartz+sillimanite+biotite with accessory minerals of rutile,zircon,and monazite.The lens margins display a fluid-induced retrogression.In order to decipher the metamorphic processes of the pelitic granulites,a combined study of BSE imaging,U-Pb dating,and trace element composition for the monazites from the metapelitic lens were conducted.Monazites from the undeformed coarse-grained granulite only record a Paleoproterozoic age(1832±7 Ma,n=40).Monazites from the other lithologies yield the inherited Paleoproterozoic age and Triassic overgrowth age.For example,monazites from the migmatite yield intercept ages of 1818±10 and 211±22 Ma(n=56)with Triassic concordant age of 223.8±2.9 Ma.The Paleoproterozoic monazites are characterized by remarkable depletion in HREE and Y with obviously negative Eu anomalies,indicating their formation equilibrated with garnet and feldspar under granulite-facies conditions.During Triassic fluid modification,the monazite bright rims assimilated Th and Si but released U,HREE,Y,and P.This process resulted in that the Triassic overgrowth monazites have higher HREE and Y contents,and lower Th and U contents with relatively low Th/U ratios.Thus,the monazites in the pelitic granulites recorded a Paleoproterozoic metamorphic event and Triassic fluid modification.The Weihai pelitic granulites might have a tectonic affinity with the North China Craton.Therefore,the Paleoproterozoic pelitic granulites were mechanically dra

关 键 词：Pelitic granulite MONAZITE PALEOPROTEROZOIC TRIASSIC Sulu orogen 

分 类 号：P534.3[天文地球—古生物学与地层学] P588.3[天文地球—地质学]