赞皇变质杂岩区西南部斜长角闪岩的地球化学、变质演化研究及其构造意义  

Geochemistry,metamorphic evolution and its tectonic implications of amphibolites in the southwest area of the Zanhuang complex

作　　者：肖玲玲[1] 卢俊生[2] 王国栋[2] 蔡佳[1] 吴春明[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国科学院大学地球科学学院,北京100049

出　　处：《岩石学报》2012年第9期2807-2818,共12页Acta Petrologica Sinica

基　　金：科技部973项目(2012CB416603);国家自然科学基金项目(40725007;41102120;40672129);中国地质调查局地质调查工作项目(1212011120150);中国地质科学院地质研究所基本科研业务费专项资金(J1117)联合资助

摘　　要：赞皇变质杂岩位于华北克拉通中部造山带中南段,阜平杂岩以南,太古代变质岩石在该杂岩区仅有零星出露。目前研究发现,在赞皇变质杂岩的西南部地区亦有太古代(含榴)斜长角闪岩出露,且与东南部的斜长角闪岩具有类似的地球化学性质,其原岩为亚碱性玄武质岩石,形成于岛弧构造环境。岩石中石榴石保留微弱的进变质生长环带,且记录了进变质、峰期变质和退变质三个阶段的矿物组合。不同阶段的温压估算结果分别为:进变质阶段约679℃和8.4kbar,高峰期变质条件位于高角闪岩相,最高温度超过702℃、最高压力大于9.3kbar,退变质阶段温度为633～636℃、压力为5.2～5.4kbar。该地区含榴斜长角闪岩拥有典型的顺时针近等温减压型(ITD)的变质作用P-T轨迹,推测赞皇变质杂岩可能卷入了华北克拉通东部陆块和西部陆块之间的俯冲-碰撞-快速隆升过程。同时,早期进变质作用阶段信息的保留为俯冲过程的存在提供了新的证据。The Zanhuang complex is located at the eastern margin of the middle segment of the nearly NS-striking Trans-North China Orogen.Previous studies suggested that the Archaean metamorphic rocks only expose in the middle-southern part of the complex.However,our new research found that（garnet-bearing） amphibolites also exposed in the southwestern part of the complex.Geochemical data indicate that protoliths of these amphibolites were possibly calc-alkaline basaltic rocks and were formed in volcanic arcs,similar to amphibolites in the southeastern part of the complex.The garnets in these rocks record weak chemical zoning,which preserve three different metamorphic mineral assemblages formed during the prograde,peak and retrograde stages.Thermobarometric computation shows that the metamorphic conditions of these rocks are^679℃ at 8.4kbar for the prograde stage（M1）,〉702℃ and 〉9.3kbar for the amphibolite facies peak stage（M2）,and 633~636℃ at 5.2~5.4kbar for the post-peak decompression stage（M3）.Clockwise P-T paths are thus yielded for the amphibolites,which is characterized by the nearly isothermal decompression（ITD） segments.This suggests that the metamorphism most likely resulted from the collisional process related to the amalgamation of the Eastern and Western blocks to form the coherent Precambrian basement of the North China Craton along the Trans-North China Orogen.Furthermore,the information of the prograde stage provides new evidence for the subduction process.

关 键 词：斜长角闪岩 地球化学 温度计 压力计 P-T轨迹 赞皇 华北中部造山带 

分 类 号：P588.125[天文地球—岩石学]