南阿尔金高压-超高温麻粒岩变质作用：大陆地壳超深俯冲与折返过程的记录  

Metamorphism of High Pressure-Ultrahigh Temperature(HP-UHT) Granulites from South Altyn Orogen: Records for Ultradeep Subduction and Exhumation of Continental Crust

作　　者：董杰 魏春景[1] 张建新[2] Dong Jie;Wei Chunjing;Zhang Jianxin(School of Earth and Space Sciences,Peking University,Beijing 100871,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]北京大学地球与空间科学学院,北京100871 [2]中国地质科学院地质研究所,北京100037

出　　处：《地球科学》2019年第12期4004-4008,共5页Earth Science

基　　金：科技部“973”项目(No.2015CB856105)

摘　　要：南阿尔金造山带是目前报道的具有最深俯冲记录的大陆超高压变质带,其内出露有高压-超高温麻粒岩,它们对深入理解大陆地壳岩石超深俯冲与折返过程具有重要意义.介绍了对南阿尔金巴什瓦克地区长英质麻粒岩和基性麻粒岩的岩相学、矿物化学、相平衡模拟及锆石U-Pb年代学研究成果.其中基性麻粒岩主要记录了深俯冲大陆地壳折返过程的变质演化:包括高压榴辉岩相、高压-超高温麻粒岩相、低压-超高温麻粒岩相及随后的近等压降温演化阶段;长英质麻粒岩除了记录与基性麻粒岩相似的折返过程外,还记录了从角闪岩相到超高压榴辉岩相的进变质演化过程.结合已有研究资料,确定超高压榴辉岩阶段峰期条件>7~9 GPa和>1000℃,可达到斯石英稳定域.锆石年代学显示两种岩石类型的原岩和变质年龄均分别在900 Ma和500 Ma左右.变质作用与年代学研究表明,南阿尔金大陆地壳岩石在早古生代发生超深俯冲至200~300 km后,折返至加厚地壳底部发生高压-超高温变质作用,随后被快速抬升至地壳浅部发生低压-超高温变质作用并经历迅速冷却.The South Altyn orogen is a typical continental ultrahigh-pressure(UHP)belt which is claimed to host the deepest subducted crustal rocks.HP-UHT granulites occurred in the belt are of significance for understanding the ultradeep subduction and exhumation of continental crust.This paper presents the results of petrography,mineral chemistry,phase equilibria modelling and zircon U-Pb dating for felsic and mafic granulites from Bashiwake area.Mafic granulites have mainly recorded the exhumation process of ultradeep continental crust,with metamorphic evolution from HP eclogite facies to HP-UHT granulite facies,further to low-pressure(LP)-UHT granulite facies conditions and the subsequent isobaric cooling.In addition to the similar exhumation to that of mafic granulites,felsic granulites have also preserved the early prograde history from amphibolite facies to UHP eclogite facies conditions.Combing previous studies,the peak conditions of UHP eclogite facies is estimated to be>7-9 GPa and>1000℃,covering the stishovite-stability field.Zircon age dating suggests that both felsic and mafic granulites have similar protolith ages of^900 Ma and metamorphic ages of^500 Ma.Metamorphic and dating studies indicate that the South Altyn continental crust was subducted to ultradeep depths of 200-300 km during the Early Paleozoic and exhumed to the bottom of a thicken crust where HP-UHT metamorphism occurred.Then the crust was uplifted rapidly to the shallow crustal level and experienced LP-UHT metamorphism followed by subsequent isobaric cooling.

关 键 词：高压一超高温变质作用 长英质麻粒岩 基性麻粒岩 大陆超深俯冲 南阿尔金 岩石学 

分 类 号：P581[天文地球—岩石学]