北羌塘宁多地区三叠纪过铝质花岗岩的成因及其地球动力学背景  

Petrogenesis and Geodynamic Setting of the Ningduo Peraluminous Granites from the North Qiangtang Terrane

作　　者：刘彬[1,2] 徐雨 马昌前[2,3] 李福林 赵少卿[1] 湛君明 孙洋[1] 黄坚[3] Liu Bin;Xu Yu;Ma Changqian;Li Fulin;Zhao Shaoqing;Zhan Junming;Sun Yang;Huang Jian(School of Geosciences,Yangtze University,Wuhan 430100,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430078,China;School of Earth Sciences,China University of Geosciences,Wuhan 430074,China;Wuhan Center,China Geological Survey(Central South China Innovation Center for Geosciences),Wuhan 430205,China)

机构地区：[1]长江大学地球科学学院,湖北武汉430100 [2]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430078 [3]中国地质大学地球科学学院,湖北武汉430074 [4]中国地质调查局武汉地质调查中心(中南地质科技创新中心),湖北武汉430205

出　　处：《地球科学》2023年第9期3296-3311,共16页Earth Science

基　　金：国家自然科学基金项目(Nos.42130309,41972066,41502050);中国地质调查局项目(Nos.12120115026901,1212011121270).

摘　　要：青藏高原中部(包括北羌塘地区)出露了大规模三叠纪中酸性岩浆活动.然而,目前人们对于这些岩浆的起源、岩石成因及其地球动力学机制等问题至今还存在较多分歧.本文以北羌塘宁多地区过铝质花岗岩体为研究对象,开展锆石U-Pb年代学、全岩和同位素地球化学等综合研究,为深入认识与理解过铝质花岗岩形成机制及青藏高原中部三叠纪构造‒岩浆演化过程等提供新的线索.宁多过铝质花岗岩的岩性为黑云母花岗闪长岩,主要由斜长石(35%~40%)、石英(25%~30%)、碱性长石(15%~20%)和黑云母(5%~10%)组成.宁多花岗岩的锆石U-Pb年龄为248±1 Ma,为早三叠世岩浆活动的产物.样品均具有中等程度的SiO_(2)和MgO含量,相对富钾和铝,总体上与强过铝质花岗岩成分特征类似.所有岩石样品相对原始地幔要明显富集Rb、K等大离子亲石元素和轻稀土元素,亏损Nb、Ta、Ti和P等高场强元素.岩石样品具有相对高的87Sr/86Sr初始比值(I_(Sr)为0.720~0.722)、相对低的ε_(Nd)(t)值(-12.4~-12.3)以及古老的两阶段模式年龄(T_(2DM)为2.02~2.03 Ga),可与北羌塘地体东南部元古代片麻岩及由前寒武纪变质基底熔融形成的S型花岗岩特征类比.宁多过铝质花岗岩具有显著高的锆饱和温度(806~845℃)和锆石Ti温度(830~1033℃),可与世界上典型高温花岗岩类的结晶温度类比.研究结果表明,这些过铝质花岗岩的形成与北羌塘前寒武纪基底物质(变杂砂岩和少量变泥质岩组分)的高温熔融有关.结合区域上多学科研究资料可以判断,在龙木错‒双湖古特提斯洋北向俯冲的背景下,板片回撤引发弧后伸展和大量玄武质岩浆底侵,进而导致这一时期古老基底物质发生高温熔融.Triassic intermediate to acid magmatism is widely distributed in the central Tibetan Plateau(including the North Qiangtang terrane).However,the magma origin,petrogenesis and geodynamic mechanism of the magmas are still poorly understood.This paper presents an integrated study of zircon U-Pb geochronology,whole-rock and isotopic geochemistry for the Ningduo peraluminous granites from the North Qiangtang terrane,aiming to provide new insights into the generation of peraluminous granites and the Triassic tectonic-magmatic evolution of the central Tibetan Plateau.The lithology of the Ningduo peraluminous granites is biotite granodiorite,which is mainly composed of plagioclase(35%-40%),quartz(25%-30%),K-feldspar(15%-20%),and biotite(5%-10%).The crystallization age of the Ningduo granites is 248±1 Ma,which could be considered as the products of the Early Triassic magmatism.The Ningduo granites have moderate contents of SiO_(2)and MgO,and relatively high contents of K and Al,which can be comparable to those of typical strongly peraluminous granites.All the samples are featured with enrichment of large ion lithophile elements(e.g.,Rb,K)and light rare earth elements,and depletion of high field strength elements(e.g.,Nb,Ta,Ti,and P),relative to the primitive mantle.They have relatively high I_(Sr) ratios of 0.720-0.722,lowε_(Nd)(t)values of-12.4 to-12.3,and old T_(2DM)ages of 2.02-2.03 Ga,similar to those of the Proterozoic gneisses and Precambrian basement-derived S-type granites.The Ningduo granites have remarkable high zirconium saturation temperatures(806-845℃)and Ti-in-zircon temperatures(830-1033℃),similar to those of typical high-temperature granites worldwide.The results indicate that the Ningduo granites were derived from partial melting of Precambrian basement rocks(greywacke and minor pelite rocks)under a high temperature condition.During the subduction of the Longmuco-Shuanghu Ocean,slab rollback triggered the back-arc extension and intense basaltic underplating,and then induced the high-temperature melti

关 键 词：过铝质花岗岩 高温花岗岩 岩石成因 三叠纪 北羌塘 岩石学 地球化学 

分 类 号：P581[天文地球—岩石学]