塔里木西南大陆边缘原特提斯洋构造演化  

Proto-Tethys Tectonic Evolution from Ordovician to Devonian in Southwestern Margin of Tarim Block,NW China

作　　者：杨鑫[1,2] 徐旭辉[1] 邓尚[1] 翟常博 孔强夫[1] 王石 Yang Xin;Xu Xuhui;Deng Shang;Zhai Changbo;Kong Qiangfu;Wang Shi(SINOPEC Petroleum Exploration and Development Research Institute,Beijing 100083,China;Key Laboratory of Petroleum Resources Research,Chinese Academy of Sciences,Lanzhou 730000,China)

机构地区：[1]中国石化石油勘探开发研究院,北京100083 [2]中国科学院油气资源研究重点实验室,甘肃兰州730000

出　　处：《地球科学》2020年第11期4153-4175,共23页Earth Science

基　　金：国家自然科学基金项目(Nos.41802135,91755211);国家重大专项(No.2017ZX05005-002)。

摘　　要：通过对塔里木西南地区奥陶系-泥盆系的钻井和露头碎屑岩样品开展锆石U-Pb年代学、地球化学和重矿物分析,探讨塔西南大陆边缘原特提斯洋的俯冲增生演化过程.碎屑锆石记录了482~443 Ma、438~425 Ma和414~406 Ma三期寒武纪以来的构造-热事件,以及840~750 Ma的新元古代裂谷岩浆事件.奥陶系-泥盆系碎屑岩具有高的SiO2含量和相对低的Al2O3和TFe2O3+MgO含量,以及弱-中等的Eu负异常、LREE相对富集和HREE分布较平坦的特征.地球化学图解反映晚奥陶统碎屑岩来源于大陆岛弧和活动大陆边缘环境,早志留世-中泥盆世期间物源区可能以大陆岛弧和被动陆缘环境为主,还间断出现少量活动大陆边缘环境,晚泥盆世以后主要呈现被动陆缘环境.重矿物组合指示早志留世至中泥盆世期间,中-酸性岩浆活动加剧,而基性岩浆活动趋弱,晚泥盆世以后陆壳基底或造山带已大规模隆升.塔西南边缘原特提斯洋构造演化以奥陶纪向北俯冲、志留纪弧后洋盆关闭-褶皱造山和泥盆纪后碰撞伸展为特征.Geochemistry,zircon U-Pb dating and heavy mineral compositional analysis were carried out for the clastic rocks from Ordovician-Devonian drilling samples,to constrain the tectonic evolution of Proto-Tethys in southwestern Tarim.The zircon grains are divided into three genetic types,i.e.magmatic zircon,metamorphic zircon and trapped or residual zircon,recording the tectonic-thermal events in the periods of the 482-443 Ma,438-425 Ma and 414-406 Ma since the Cambrian,as well as the Neoproterozoic rift magma events between 840 Ma and 750 Ma.The clastic rocks have high content of SiO2 but relatively low content of Al2 O3 andTFe2 O3+MgO.They are characterized by right-dip chondrite-normalized REE pattern and flat HREE distribution,with weak to medium Eu negative anomaly.The ratios of trace elements,such as Th/U ratio,Cr/Zr ratio,Rb/Cs ratio,and La/Sc,suggests the terrigenous clastic components were derived from the felsic rocks in upper crust.It is assumed that the tectonic setting of sedimentary basin was characterized by continental island arc and active continental margin in late Ordovician.From the Early Silurian to Middle Devonian,the provenance was then predominated by continental island arc and passive continental margin,and mingled with active continental margin slightly.After the Late Devonian,it gradually changed over to evidential passive continental margin.It is indicated by the heavy minerals that the medium to acid magma activity became frequent while the basic magma activity became quiet during the time from Early Silurian to Middle Devonian,and the mountain uplifted massively since Late Devonian.Thus,the tectonic evolution of Proto-Tethys in south-western margin of Tarim could be divided into three stages,i.e.the northward subduction in Ordovician,the closure of back-arc ocean and folding orogeny in Silurian,and post-collision extension in Devonian.

关 键 词：原特提斯洋 塔西南 西昆仑 早古生代 构造环境 构造地质 

分 类 号：P548[天文地球—构造地质学]