柴达木盆地东部基底花岗岩类岩浆活动的化学地球动力学  

Chemical Geodynamics of Granitic Magmatism in the Basement of the Eastern Qaidam Basin,Northern Qinghai-Tibet Plateau

作　　者：陈宣华[1,2] 尹安 George GEHRELS 李丽[1,2] 蒋荣宝[1,2] 

机构地区：[1]国土资源部新构造运动与地质灾害重点实验室,北京100081 [2]中国地质科学院地质力学研究所,北京100081 [3]Department of Earth and Space Sciences,University of California,Los Angeles [4]Department of Geosciences,University of Arizona

出　　处：《地质学报》2011年第2期157-171,共15页Acta Geologica Sinica

基　　金：中国地质科学院地质力学研究所基本科研业务费项目(编号DZLXJK200703);国家自然科学基金项目(编号40342015)资助的成果

摘　　要：柴达木盆地东部是连接秦岭、祁连、昆仑三大造山带的关键构造部位,发育了以晚二叠世—中三叠世(P-T)花岗岩类为主的古特提斯域深成岩浆活动。岩石地球化学分析表明,柴达木盆地东部基底P-T花岗岩类形成于大洋环境,主要为I型花岗岩类。该期花岗岩类可分为两个时间演化系列,早期为钾长花岗岩—花岗闪长岩—英云闪长岩—闪长岩系列,晚期为碱性花岗岩—钾长花岗岩—花岗闪长岩系列,均具有与经典的鲍文反应系列相反(即反鲍文系列)的演化趋势,反映了深成岩浆的动态混合作用模式。Nd-Sr-Pb-O同位素组成特征说明,柴达木盆地东部基底P-T花岗岩类具有年轻地壳的特征,其来源主要与富集地幔EMⅡ源区有关,具明显的造山带与上地壳Pb同位素特征。柴达木盆地东部基底与西秦岭及扬子块体中生代花岗岩类的Pb同位素组成具有相似性,说明了柴达木盆地基底与扬子地块具有亲缘性。研究表明,来自地幔的基性岩浆底侵作用,以及幔源镁铁质岩浆与壳源长英质岩浆之间的混合作用,可能是柴达木盆地东部基底地壳生长的重要方式。The eastern margin of the Qaidam Basin lies in a key tectonic location connecting the Qinling,Qilian and Kunlun orogens.The Permian Triassic（P-T）I-type granitoids in the basement of the eastern Qaidam Basin are parts of the intrusive magmatism of the Paleo-Tethyan orogeny formed in ocean environment.Lithogeochemical analyses,combined with previous LA ICP-MS zircon U-Pb dating,reveal two time series of P-T granitoids.The early series is composed of K-feldspar granites,granodiorites,tonalities,and diorites,and the later series is composed of alkali granites,K-feldspar granites,and granodiorites.Both of them have lithogeochemical trends of anti-Bowen＇s reaction series,opposite to that of classical Bowen＇s reaction series.Nd-Sr-Pb-O isotope compositions of P-T granitoids showes characteristics of young crust formed in orogeny and upper crust with a close relationship to enriched mantle（EM Ⅱ）source.The Pb composition of P-T granitoids from the basement of the eastern Qaidam Basin is very similar to that of the Mesozoic granitoids from West Qinling Orogeny and Yangtze Block,suggesting the tectonic affinity between the basement of the eastern Qaidam Basin and the Yangtze Block.It is suggested that,underplating of mafic magma from the mantle and dynamic mixing between the mantle-derived mafic and crust-derived felsic magmas,may act an important role in the crust growth of the basement of the Qaidam Basin.

关 键 词：化学地球动力学 深成岩浆活动 二叠纪—三叠纪 柴达木盆地东部 秦-祁-昆接合带 

分 类 号：P541[天文地球—构造地质学]