柴达木盆地北缘早奥陶世陆-弧碰撞及弧后前陆盆地——来自碎屑岩地球化学的证据  

Early Ordovician Continental-Arc Collision and Retroarc Foreland Basin on the Northern Margin of Qaidam Basin:Geochemical Evidence from Clastic Rocks

作　　者：孙娇鹏 陈世悦[1] 马寅生[2] 彭渊[2] 邵鹏程 马帅 代昆[2] 郑策[2] 

机构地区：[1]中国石油大学(华东)地球科学与技术学院,山东青岛266580 [2]中国地质科学院地质力学研究所,北京100081

出　　处：《地质学报》2016年第1期80-92,共13页Acta Geologica Sinica

基　　金：中国地质调查局地质调查项目"柴达木盆地油气资源潜力评价"(编号1212010818054)和"柴达木盆地古生代油气资源调查评价"(编号1212011120964)联合资助成果

摘　　要：奥陶纪是柴达木盆地北缘早古生代碰撞造山演化的重要时期,柴达木地块与滩间山岛弧碰撞起始时限以及欧龙布鲁克海盆盆地类型、构造-古地理格局一直存在争议。本文在对欧龙布鲁克地块早奥陶世碎屑岩沉积野外观测及室内分析的基础上,测试了30个砂泥岩样品的主量元素、微量元素及稀土元素含量。结果表明,石灰沟组碎屑岩建造具有快速堆积、低成分成熟度、低结构成熟度的特征;该套碎屑岩沉积于活动大陆边缘背景下的弧后前陆盆地,碎屑物质来自南部由大陆上地壳与岛弧物质组成的上隆基底;早奥陶世（488~472 Ma）柴达木地块与滩间山岛弧陆-弧碰撞已经开始,但陆-弧碰撞起始时间不会早于493Ma。在此基础上,结合前人研究成果,认为早古生代欧龙布鲁克地块处于滩间山岛弧北部,盆地沉降、沉积演化受柴达木盆地北缘洋盆俯冲及柴达木地块-滩间山岛弧碰撞控制,寒武纪发育弧后伸展盆地,奥陶纪初期转为弧后挤压前陆盆地,弧后伸展与弧后挤压、沉积体系转换发生在490~480Ma之间。该成果从沉积学角度为柴达木盆地北缘陆-弧碰撞起始时限提供了新的制约。Ordovician is an important period for the Early Paleozoic collisional orogenic evolution in the northern margin of Qaidam basin, but the initial timing of continent-arc collision, basin type and paleostructure- paleogeographic pattern have long been in dispute. This study, based on field observations and lab analyses of the Early Ordovician clastic deposition in the Oulongbuluke block, tested 30 mud sand samples for major elements, trace elements and rare earth elements. Results indicate that elastic rocks of the Shihuigou Formation are characterized by rapid accumulation, low maturation ot texture and component. The series of elastic rocks deposited in retroarc foreland under the background of active continental margin, with detritus derived from the southern upwelling basement composed by upper continental crust and island arc. Continental-arc collision caused by Qaidam block and Tanjianshan island arc had started since the Early Ordovician （488～472Ma）, but the initial timing of continent-are collision was no earlier than 493 Ma. Combining previous research results, this study proposes the following understanding. The Oulongbuluke block was located to the north of Tanjianshan island arc during Early Paleozoie Era. The basin subsidence and sedimentary evolution was controlled by oceanic crust subduction and continental-arc collision. Retroarc stretch basin developed during Cambrian period and then transferred to retroarc extrusion foreland basin in the Early Ordovician. Retroarc stretch and retroarc compression occurred approximately 490～480 Ma long with sedimentary system transformation. The conclusions presented in this study provide new sedimentary constraint on the initial timing of continent-arc collision

关 键 词：柴达木盆地北缘 早奥陶世 碎屑岩 地球化学 陆-弧碰撞 弧后前陆盆地 

分 类 号：P534.42[天文地球—古生物学与地层学]