石榴子石-石英弹性压力计对北祁连HP/LT变质岩进变质过程的限定  

Prograde process of the North Qilian HP/LT metamorphic rocks:Constraints from quartz-in garnet elastic barometry

作　　者：赵晓轩 张建新[1] 张聪[1] 毛小红[1] 武亚威 ZHAO XiaoXuan;ZHANG JianXin;ZHANG Cong;MAO XiaoHong;WU YaWei(SinoProbe Laboratory,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;China University of Geosciences,Beijing 100083,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]中国地质科学院地质研究所,自然资源部深地科学与探测技术实验室,北京100037 [2]中国地质大学,北京100083 [3]北京大学地球空间科学学院,北京100871

出　　处：《岩石学报》2024年第12期3847-3860,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(U2344214);中国地质科学院基本科研业务费项目(JKYZD202310)联合资助。

摘　　要：北祁连早古生代大洋俯冲带发育HP/LT变质带,以出露低温榴辉岩、蓝片岩和相关的HP/LT变沉积岩为特征。确定大洋俯冲带不同类型变质岩的温压条件对限定俯冲带的热结构和俯冲动力学过程至关重要。在北祁连早古生代大洋俯冲带中,已有的研究主要通过传统温压计和相平衡模拟来确定榴辉岩及相关岩石的温压条件,而不同类型的岩石是否经历了相同的变质条件及演化历史仍存在很大争议。显微激光拉曼光谱矿物包裹体弹性压力计基于物理学的模型,可以有效避免化学不平衡造成的计算偏差。本文利用石榴子石-石英弹性压力计,结合金红石的Ti温度计,来限定北祁连HP/LT变质带东段百经寺地区榴辉岩和变沉积岩的进变质过程中的温压条件变化历史。电子探针分析和成分面扫描显示榴辉岩和变沉积岩的石榴子石具有生长环带,这些石榴子石中石英包裹体的弹性压力计和金红石包裹体的Zr温度计结果显示,北祁连百经寺地区的榴辉岩石榴子石生长的压力范围为1.18~1.98GPa,蓝片岩中石榴子石生长的压力范围为1.32~2.02GPa,石榴云母片岩中石榴子石生长的压力范围为1.63~2.10GPa;这些结果显示不同样品均显示出压力条件从核部到幔(边)部升高的变化特征,且不同样品中石榴子石-石英包裹体的最大捕获温度压力条件大致一致的进变质温压变化历史,表明北祁连百经寺HP/LT岩片在俯冲过程中作为整体经历了相同的构造热历史。The HP/LT(high pressure/low temperature)metamorphic zone in the Early Paleozoic North Qilian orogenic belt is characterized by exposure of low-temperature eclogite,blueschists and associated metasedimentary rocks.Determining the temperature and pressure conditions of different types of HP/LT metamorphic rocks is crucial to constrain the thermal structure and geodynamics of subduction zones.The previous studies utilized conventional geothermobarometries and phase equilibrium modeling to constrain the temperature and pressure conditions of eclogites and associated rocks,but it remains controversial as to whether different types of rocks have experienced the same metamorphic evolution history.The elastic barometry,utilizing the residual stress preserved in sealed mineral inclusions,is based on a physics model and can effectively avoid calculation deviations caused by chemical imbalance.In this paper,quartz-in-garnet elastic barometry,combining with Zr-in-rutile thermometry,is employed to constrain the prograde pressure and temperature conditions of eclogites,blueschist and metasedimentary rocks in the Baijingsi HP/LT slice of the North Qilian HP/LT metamorphic belt.The microprobe analysis and composition mapping show that garnets preserved prograde growth zoning.The results that employ quartz inclusion-in-garnet barometry reveals the pressure conditions of garnet growth ranging from 1.18GPa to 1.98GPa for eclogites,and from 1.32GPa to 2.02GPa for Omp-bearing blueschist,and from 1.63GPa to 2.10GPa for micaschist.The data suggest that eclogites and associated rocks in the Baijingsi HP/LT slice experienced similar prograde metamorphic history and the formation of the Baijingsi eclogite and their host rocks as a coherent slice during the Early Paleozoic oceanic subduction.

关 键 词：弹性压力计 拉曼光谱 石英包裹体 榴辉岩 变沉积岩 北祁连 

分 类 号：P575.1[天文地球—矿物学] P588.344[天文地球—地质学] P588.348