东南极哈姆峰地区假玄武玻璃的显微构造、年代学及其地质意义  

Microstructure and geochronology of pseudotachylite from the Hamm Peak,East Antarctica,and its geological significances

作　　者：刘建民[1,2,3] 刘晓春 赵越[1,2,3] 张拴宏 徐刚[1,2,3] 董树文 毛骞[5] 陈柏林 LIU Jianmin;LIU Xiaochun;ZHAO Yue;ZHANG Shuanhong;XU Gang;DONG Shuwen;MAO Qian;CHEN Bailin(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Research Center of Polar Geosciences,China Geological Survey,Beijing 100081,China;Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Ministry of Natural Resources,Beijing 100081,China;School of Earth Science and Engineering,Nanjing University,Nanjing 210023,Jiangsu,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]中国地质调查局极地地学研究中心,北京100081 [3]自然资源部古地磁与古构造重建重点实验室,北京100081 [4]南京大学地球科学与工程学院,江苏南京210023 [5]中国科学院地质与地球物理研究所,北京100029

出　　处：《地质力学学报》2021年第5期747-758,共12页Journal of Geomechanics

基　　金：国家自然科学基金(41941004)。

摘　　要：发育在东南极普里兹湾西南部哈姆峰地区麻粒岩相花岗质片麻岩中的假玄武玻璃沿着近东西向断裂带分布。显微构造特征表明,该地假玄武玻璃基质中普遍发育球粒结构及树枝状、放射状-针状等不同形状及组合的矿物微晶体,说明这些假玄武玻璃是地震断层快速滑移过程中摩擦熔融作用的产物。假玄武玻璃中的微晶体矿物组合大体分为两种,它们分布在构造带不同地段:一种是以“紫苏辉石+斜长石”组合为主,分布于构造带东北部地段;一种是以“黑云母+斜长石+钾长石+石英”的组合为主,分布于构造带西南部地段,说明沿构造带不同部位构造环境及应力分布的不均匀性。同时,微晶体中富铝紫苏辉石的存在,表明假玄武玻璃形成过程及其后期的结晶过程可能处于高温(麻粒岩相)的构造环境下。假玄武玻璃的基质全岩K-Ar年龄为878.1±16.8 Ma,全岩^(40)Ar/^(39)Ar年龄谱系中所记录的年龄值主要集中在925~626 Ma。结合区域对比看,假玄武玻璃应该形成于格林维尔期构造事件。The pseudotachylite in granulite facies granitic gneisses from the Hamm Peak,southwestern Prydz Bay,East Antarctica,occurs along the east-west-trending ductile-brittle shear zone.The characteristics of microstructure show that the pseudotachylite was formed by the frictional-melt during the rapid faulting along the paleoseismic zone.This inference is supported by the common presence of spherulites and different morphological microlites,such as skeletal,dendritic,acicular and globular in the matrix of pseudotachylite.There exist two kinds of microlite mineral assemblage.One consists mainly of hyperite and plagioclase,which developed in the northeastern part of the shear zone.The other consists of biotite,plagioclase,alkali feldspar and quartz,etc,which developed in the southwestern part of the shear zone.The occurrence of different kinds of microlite mineral assemblage indicates the differences of tectonic surrounding and stress distribution along different parts of the shear zone.Moreover,the presence of aluminous-rich hyperite may indicates the relatively high temperature and high pressure in the ambient physical condition during the pseudotachylite formation and crystallization afterwards,i.e.,under the granulite facies conditions.The K-Ar age of bulk matrix of pseudotachylite is 878.1±16.8 Ma.Bulk^(40)Ar/^(39)Ar step-heating release spectrum gave the varying ages mainly from 925 to 626 Ma.Combined with the regional comparison,we conclude that the pseudotachylite formed during the Grenvillian tectonic events.

关 键 词：显微构造 微晶体 富铝紫苏辉石 K-Ar和^(40)Ar/^(39)Ar年代学 假玄武玻璃 哈姆峰 东南极 

分 类 号：P616.3[天文地球—矿床学] P728.2[天文地球—地质学]