秦岭造山带涝峪地区宽坪岩群变质作用温压条件及原位Rb-Sr年代学研究  

Metamorphic P-T Conditions and In-situ Rb-Sr Geochronology of the Kuanping Group in the Laoyu Area of the Qinling Orogenic Belt

作　　者：田智博 苟龙龙[1] 徐晓飞 刘学锋 毛振宇 TIAN Zhibo;GOU Longlong;XU Xiaofei;LIU Xuefeng;MAO Zhenyu(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest university,Xi'an 710069,China)

机构地区：[1]西北大学,大陆动力学国家重点实验室,陕西西安710069

出　　处：《西北地质》2025年第1期1-26,共26页Northwestern Geology

基　　金：国家自然科学基金面上项目“秦岭造山带喂子坪–宝鸡太白地区秦岭杂岩麻粒岩相变质作用及构造意义”(42172059);大陆动力学国家重点实验室项目(SKLCD-04)联合资助。

摘　　要：秦岭造山带涝峪地区发育宽坪岩群的典型剖面,是研究宽坪岩群变质变形、构造热历史的重要区域。然而,由于缺乏对该地区宽坪岩群变质温压条件和年代学的约束,导致区域变质与多期变形事件的关系及地质意义认识仍不清楚。笔者以该地区宽坪岩群SN向剖面中的二云母石英片岩、含石榴子石二云母石英片岩、绿片岩和大理岩为研究对象,开展了详细的岩相学研究。在此基础上,重点对二云母石英片岩和含石榴子石二云母石英片岩进行了黑云母Ti温度计、多硅白云母地质压力计、变质相平衡模拟和原位LA–ICP–MS黑云母和白云母Rb–Sr年代学研究,进而探讨了涝峪地区宽坪岩群经历多期构造热事件的意义。野外和岩相学观察发现二云母石英片岩和绿片岩发生了强烈的变形,金云母大理岩经历了强烈的糜棱岩化作用。黑云母Ti温度计和多硅白云母压力计限定得到二云母石英片岩样品KP-3和KP-4的变质温压条件为300~500℃、2.0~8.0 kbar,对应的平均值为440℃、4.0 kbar。黑云母Ti温度计限定得到含石榴子石二云母石英片岩样品KP2202的变质温度为652~683℃。变质相平衡模拟P–T视剖面图计算得到二云母石英片岩样品KP-3和KP-4的变质温压条件为400~480℃和2.0~10 kbar;而含石榴子石二云母石英片岩样品KP2202的变质温压条件为645~680℃、8.0~9.0 kbar。综合地质温压计和相平衡模拟的结果,可以确定二云母石英片岩为绿片岩相变质作用的产物,而含石榴子石二云母石英片岩经历了低角闪岩相变质作用。原位LA–ICP–MS黑云母和白云母Rb–Sr分析显示二云母石英片岩记录两期等时线年龄,分别为~290 Ma和~155 Ma,而含石榴子石二云母石英片岩记录的等时线年龄为~110 Ma。因此涝峪地区宽坪岩群中的二云母石英片岩记录了3期等时线年龄,分别为~290 Ma、~155 Ma和~110 Ma。结合前人的研究结果,3期等�The laoyu area of the Qinling orogenic belt has a typical section of the Kuanping group,which is important for studying the metamorphism,deformation,and tectonothermal history of the Kuanping group.However,the metamorphic P–T conditions and chronology of the Kuanping group in this region are still lacking,which hinders our understanding of the relationship between its regional metamorphism and later deformation events,as well as their geological significances.In this study,detailed petrographic studies were carried out on two–mica quartz schist,garnet–bearing two–mica quartz schist,greenschist,and marble in the north–south section of the Kuanping group in this area.Based on this,the geological significances of multiple tectonothermal events that the Kuanping group in the Laoyu region underwent were examined with a focus on two-mica quartz schist and garnet–bearing two–mica quartz schist using Ti–in–biotite thermometry,phengite geobarometry,phase equilibrium modelling,and in situ LA–ICP–MS biotite and muscovite Rb–Sr dating.According to field and petrographic observations,two–mica quartz schist and greenschist were both significantly deformed,and phlogopite marble suffered strong mylonitization.The Ti–in–biotite thermometer and phengite geobarometer yielded the metamorphic PT conditions of 300~500℃ and 2.0~8.0 kbar(average values are 440℃and 4.0 kbar)for the two–mica quartz schist samples KP-3 and KP-4.The Ti–in–biotite thermometry constrained the metamorphic temperature of the garnet–bearing two–mica quartz schist sample KP2202 to be 652~683℃.According to the PT pseudosection modeling,the metamorphic PT conditions of the two–mica quartz schists and and the garnet–bearing two–mica quartz schists are 400~480℃and 2.0~10 kbar,and 645~680℃ and 8.0~9.0 kbar,respectively.On the basis of the results from the geothermobarometry and phase equilibrium modelling,the two–mica quartz schist is the consequence of greenschist–facies metamorphism,whereas the garnet–bea

关 键 词：变质岩石学 宽坪岩群 相平衡模拟 原位Rb–Sr年代学 秦岭造山带 涝峪 

分 类 号：P588.3[天文地球—岩石学]