西峡-内乡地区秦岭岩群变质独居石和锆石的U-Pb定年  

LA-ICP-MS U-Pb dating of metamorphic monazite and zircon of the Qinling metamorphic complex,Xixia and Neixiang areas,Henan Province

作　　者：梁爽 张谦 刘嘉惠 李真 闫全人 吴春明 LIANG Shuang;ZHANG Qian;LIU JiaHui;LI Zhen;YAN QuanRen;WU ChunMing(College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院大学地球与行星科学学院,北京100049

出　　处：《岩石学报》2021年第12期3797-3814,I0009-I0016,共26页Acta Petrologica Sinica

基　　金：中国科学院前沿科学项目(QYZDJ-SSW-DQC036)资助.

摘　　要：西峡-内乡地区位于北秦岭造山带东部,出露黑云斜长片麻岩、变质砂岩、石英片岩、石墨大理岩、石榴角闪岩等变质岩石。激光拉曼测试表明,变质岩锆石与独居石包裹体中,未发现高压-超高压变质特征矿物。值得注意的是,显微岩相研究也未见到多期变质作用的证据。对变质独居石和变质锆石进行的LA-ICP-MS U-Pb定年表明,副变质岩记录的变质高峰期时代为414~405Ma,石榴角闪岩记录的变质高峰期时代为401~379Ma,属晚志留世-中泥盆世。区内岩石普遍经历了角闪岩相变质作用,变质高峰期P-T条件为660~710℃/0.53~1.02GPa,属于中压变质相系。不同变质岩的变质高峰期压力条件差异明显,说明这些岩石俯冲深度不同,在折返阶段才以构造岩片的形式混杂在一起。各种变质岩中退变质矿物组合普遍不发育,暗示抬升速率较快。Metapelite,metasandstone,quartzite,marble and garnet amphibolite expose in the Xixia and Neixiang areas,eastern North Qinling Orogenic Belt.No(ultra-)high pressure mineral inclusions were found within the metamorphic monazite or zircon through laser Raman investigation,and no petrographic evidences suggest they experienced polymetamorphism.LA-ICP-MS U-Pb dating of metamorphic monazite and zircon suggest that the metamorphic peak occurred at 414~405Ma recorded by metapelite or 401~379Ma by amphibolite,i.e.,Late Silurian to Middle Devonian.The rocks experienced amphibolite facies metamorphism with peak P-T conditions estimated to be 660~710℃/0.53~1.02GPa,which is ascribed to the medium P/T facies series.However,significant diverse pressure conditions of these rocks imply that they reached different depths and later they were amalgamated in the tectonic exhumation.Ubiqutous absence of retrograde mineral assemblages imply that the exhumation was relatively fast.

关 键 词：LA-ICP-MS U-Pb定年 变质作用 内乡 西峡 北秦岭造山带 秦岭岩群 

分 类 号：P588.34[天文地球—岩石学] P597.3[天文地球—地质学]