柴北缘超高压带中锡铁山榴辉岩的变质时代  

HP/UHP metamorphic time of eclogite in the Xitieshan terrane,North Qaidam UHPM belt,NW China

作　　者：宋述光[1] 张聪[1] 李献华[2] 张立飞[1] 

机构地区：[1]教育部造山带与地壳演化重点实验室北京大学地质系,北京100871 [2]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029

出　　处：《岩石学报》2011年第4期1191-1197,共7页Acta Petrologica Sinica

基　　金：国家基础科学发展规划项目(2009CB825007);国家自然科学基金项目(40773012;40825007;40821002)联合资助

摘　　要：锡铁山地体位于柴北缘超高压变质带的中部,是柴北缘超高压变质带的重要组成部分。该地体由花岗质片麻岩、泥质片麻岩和相对较少的榴辉岩透镜体组成。大部分榴辉岩都经历了不同程度的后生合晶和角闪岩相退化变质改造。虽然近年来进行了大量的锆石U-Pb年代学研究,但榴辉岩相高压-超高压变质的时代一直存在争议,并且以前对锡铁山榴辉岩相变质时代的认识一直与相邻的绿梁山、鱼卡和其东部的都兰等地区的超高压变质年龄有明显的冲突。本文通过锡铁山榴辉岩锆石U-Pb年代学的研究,获得榴辉岩相变质锆石的206Pb/238U加权平均年龄为433±3Ma,与鱼卡地区榴辉岩的形成年龄一致,代表大陆俯冲时期的高压-超高压变质年龄。该研究对进一步了解锡铁山榴辉岩地体的变质演化和大陆地壳深俯冲有重要意义。Xitieshan terrane is located in the middle part of the North Qaidam ultrahigh-pressure （UHP） metamorphic belt.It is one of the important terranes in the belt and consists of granitic and pelitic gneisses with lesser lensoid blocks of eclogite and serpentinized peridotite without garnet.Most eclogite blocks were retrograde to varying extent with symplectite and amphibolite overprinting.Although numbered zircon U-Pb geochronological data have been reported in recent years,time for HP-UHP eclogite-facies metamorphism remains debatable,and interpretations for the previous age data contradict against UHP metamorphic ages that have determined from the Yuka eclogite,Luliangshan garnet peridotite and coesite-bearing metapelite in Dulan.Using techniques of CL and SIMS analyses,combining studies on mineral inclusions in zircons,we obtained an eclogite-facies metamorphic age of 433±3Ma （weighted mean）.This age is consistent with metamorphic ages of Yuka eclogites and should represent HP-UHP metamorphic time for continental subduction.This study plays important role in understanding metamorphic evolution and deep subduction of continental crust in the Xitieshan eclogite-bearing terrane.

关 键 词：高压-超高压变质带 榴辉岩 变质年龄 大陆俯冲 锡铁山地体 柴北缘 

分 类 号：P588.3[天文地球—岩石学]