柴达木北缘鱼卡河榴辉岩变质时代及其折返过程  

Metamorphic age and exhumation process of Yukahe eclogite in northern margin of Qaidam Basin

作　　者：杨乐 李小亮 张万辉 冶玉花 覃艳引 李定武 王依 张松涛 YANG Le;LI Xiaoliang;ZHANG Wanhui;YE Yuhua;QIN Yanyin;LI Dingwu;WANG Yi;ZHANG Songtao(Geological Science and Technology Branch,Qinghai Provincial Non-ferrous Metal Geological and Minerals Exploration Bureau,Xining 810000,China;Qinghai Key Laboratory of Concealed Mineral Exploration,Qinghai Provincial Non-ferrous Metal Geological and Minerals Exploration Bureau,Xining 810007,China;No.1 Geological Exploration Institute,Qinghai Provincial Non-ferrous Metal Geological and Minerals Exploration Bureau,Xining 810007,China;Guangxi Institute of Geological Survey Guangxi Bureau of Geology and Mineral Prospecting and Exploitation,Nanning 530023,China;Anhui Branch of China National Geological Exploration Center of Building Materials Industry,Hefei 230031,China)

机构地区：[1]青海省有色地质矿产勘查局地质科技处,西宁810000 [2]青海省有色地质矿产勘查局青海省隐伏矿勘查重点实验室,西宁810007 [3]青海省有色地质矿产勘查局青海省有色第一地质勘查院,西宁810007 [4]广西壮族自治区地质矿产勘查开发局广西壮族自治区地质调查院,南宁530023 [5]中国建筑材料工业地质勘查中心安徽总队,合肥230031

出　　处：《世界地质》2022年第3期510-521,共12页World Geology

基　　金：青海省有色地质矿产勘查局局管项目(青色地[2021]59号)。

摘　　要：为揭示柴北缘超高压变质带的变质时代与折返过程,利用Ar-Ar同位素定年法对鱼卡河和锡铁山地区的榴辉岩进行了研究。结果表明,鱼卡河榴辉岩的峰期变质作用发生在早—中奥陶世(477~466 Ma),而锡铁山榴辉岩中的韭闪石年龄((407±4)Ma)指示了早泥盆世的退变质时间。综合前人研究成果可知柴北缘超高压变质带形成于495~421 Ma,且具有明显的两阶段特征(477~466 Ma与434~421 Ma),其中早阶段为洋壳俯冲的产物,晚阶段为大洋关闭后陆壳深俯冲的结果。祁连陆块与柴达木—东昆仑板块在早泥盆世发生不同方位的俯冲挤压,并导致超高压变质带折返,超高压变质体普遍发生部分熔融和退变质,出现以榴辉岩为中心向外榴辉岩-榴闪岩-斜长角闪岩-花岗片麻岩渐变过渡的退变质带。In order to reveal the metamorphic timing and exhumation process of the ultrahigh pressure(UHP)metamorphic belt in the northern margin of Qaidam Basin(NMQB),Ar-Ar isotopic dating was used to study the eclogites from the Yukahe and Xitieshan areas.The analytical results show that the peak metamorphic timing of the Yukahe eclogites took place in Early-Middle Ordovician(477~466 Ma),and the pargasite age of(407±4)Ma obtained from the Xitieshan eclogites represents the retrograde metamorphic time at Early Devonian.Combined with previous researches,it can be concluded that the UHP metamorphic belt in the NMQB was formed at 495~421 Ma with two significant stages of 477~466 Ma and 434~421 Ma,in which the early stage metamorphism being the product of oceanic crust subduction and the late stage metamorphism resulting by deep subduction of continental crust after ocean closure.The Qilian Massif subducted towards the Qaidam-Eastern Kunlun Plate in different directions in Early Devonian,resulting in the exhumation of the NMQB UHP metamorphic belt.Significant partial melting and retrograde metamorphism are common in the UHP metamorphic bodies,which appears a retrograde metamorphic belt with eclogite as the center and garnet amphibolite-amphibolite-granitic gneiss as the transition outward.

关 键 词：柴达木北缘 超高压变质带 榴辉岩 Ar-Ar同位素定年 折返过程 

分 类 号：P588.3[天文地球—岩石学]