西昆仑碰撞后钾质火山岩岩浆作用过程--以普鲁和康西瓦火山群为例  

STUDY ON THE MAGMATIC PROCESSES OF POST-COLLISIONAL POTASSIC VOLCANIC ROCKS FROM WEST KUNLUN:TAKING THE PULU AND KANGXIWA VOLCANIC ROCKS AS EXAMPLES

作　　者：丁冉 栾鹏 于红梅[1,2] 魏费翔 赵波 杨文健[1,2] 许建东 DING Ran;LUAN Peng;YU Hong-mei;WEI Fei-xiang;ZHAO Bo;YANG Wen-jian;XU Jian-dong(Changbaishan Volcano National Observation and Research Station,Institute of Geology,China Earthquake Administration(CEA),Beijing 100029,China;Key Laboratory of Seismic and Volcanic Hazards,Institute of Geology,China Earthquake Administration,Beijing 100029,China;China Academy of Natural Resources Economics,Beijing 101149,China)

机构地区：[1]中国地震局地质研究所,吉林长白山火山国家野外科学观测研究站,北京100029 [2]中国地震局地震与火山灾害重点实验室,北京100029 [3]中国自然资源经济研究院,北京101149

出　　处：《地震地质》2024年第2期312-335,共24页Seismology and Geology

基　　金：吉林长白山火山国家野外科学观测研究站专项(NORSCB20-02);中国地震局地质研究所基本科研业务专项(IGCEA1904)共同资助。

摘　　要：西昆仑处于青藏高原西北缘,该地区岩浆活动强烈,形成了多个大小、规模不等的碰撞后钾质火山岩群,但这些钾质火山岩的岩浆作用过程依然不清晰。为了研究西昆仑地区的岩浆作用过程,文中选取了该区域的普鲁和康西瓦火山群作为研究对象,对其火山岩进行了全岩主量元素含量、斑晶结构和成分分析,以及晶体大小分布(CSD)和岩浆结晶温压条件研究。结果表明,尽管两地的岩浆具有相似的源区,但这2个火山群的岩石类型和矿物组成存在显著差异。普鲁火山岩为一套粗安岩和玄武粗安岩的组合,斑晶由斜长石、橄榄石、单斜辉石和少量斜方辉石构成;康西瓦火山岩主要为响岩质碱玄岩,斑晶矿物为单斜辉石、黑云母和少量橄榄石及斜长石。结合斑晶结构、环带成分和CSD曲线形态分析认为,普鲁火山岩经历了不同演化程度的岩浆混合;而康西瓦火山岩仅发生了岩浆自混,且减压造成了斑晶的大量熔蚀。矿物-熔体平衡温压计计算表明,普鲁火山岩的平衡温度为1036~1218℃,平衡压力为5.1~9.9kbar,对应的深度为19.4~37.3km;康西瓦火山岩的平衡温度为1154~1282℃,平衡压力为1.2~11.6kbar,对应深度为4.3~43.7km。康西瓦地区的平衡压力变化范围较大,可能与所处的断裂带有关。文中定量化研究了西昆仑地区的后碰撞钾质火山岩的岩浆作用过程,补充了以往对该区域火山岩中斑晶CSD的研究,揭示了岩浆在地壳岩浆储库内的运移和演化过程,为青藏高原西北缘及其周边地区的火山活动研究提供了重要信息。The West Kunlun region is located in the northwest margin of the Qinghai-Xizang Plateau.Due to the subduction and collision of the Indian plate,this region has many post-collisional potassic volcanic areas of different sizes.Scholars have conducted many volcanic geology and petro-geochemistry work in the West Kunlun volcanic area,mainly focusing on the origin of deep magmas and plate dynamics.However,the magmatic processes of these potassic volcanic rocks are still unclear.To reveal the magmatic processes in the West Kunlun region and understand the mechanism of volcanic eruption,we analyzed the whole-rock major elements,structure and compositions of the phenocrysts,the crystal size distribution(CSD),and magma crystallization temperature and pressure conditions of the Pulu and Kangxiwa volcanic rocks.The results show that the magma sources of the two volcanic regions are close and their trace element characteristics are similar.Still,their rock types and mineral compositions are significantly different.The Pulu volcanic rocks are mainly trachyandesite and basaltic trachyandesite.The phenocrysts are composed of plagioclase,olivine,clinopyroxene and a small amount of orthopyroxene.The Kangxiwa volcanic rocks are mainly phonotephrite,consisting of clinopyroxene,biotite,and a small amount of olivine and plagioclase.The erosion and zonation of plagioclase,olivine and clinopyroxene were observed under a microscope.There are Nb-Ta and Ti negative anomalies in the two regions,with relative enrichment of large ion lithophile elements(LILF)and light rare earth elements(LREE),indicating that the magma source area has the characteristics of island arc magma,which is related to plate subduction.Based on the analysis of previous Sr-Nd datas,we suggest that the magmas from these two volcanic areas originated from enriched sources.According to the erosion characteristics,zonal composition data,and the concave CSD pattern,we suggest that the magma in Pulu mixed with acidic magma,whereas the magma in Kangxiwa may only mix with the

关 键 词：显微结构 晶体大小分布 岩浆混合 普鲁火山群 康西瓦火山群 西昆仑火山区 

分 类 号：P317.3[天文地球—固体地球物理学]