拉萨—羌塘地体碰撞时限:来自班公湖—怒江缝合带中段多尼组沉积的约束  

Timing of the Lhasa⁃Qiangtang Collision:Constraints from the sedimentary records of the Duoni Formation from the middle segment of the Bangong⁃Nujiang suture zone

作　　者：朱志才 翟庆国[1] 胡培远[1] 唐跃[1] 王海涛[1] 王伟[1] 吴昊[1] 黄智强 ZHU ZhiCai;ZHAI QingGuo;HU PeiYuan;TANG Yue;WANG HaiTao;WANG Wei;WU Hao(HUANG ZhiQiang Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院地质研究所,自然资源部深地动力学重点实验室,北京100037

出　　处：《沉积学报》2020年第4期712-726,共15页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(91755103,41874040);中国科学技术部(2016YFC0600304);第二次青藏高原综合科学考察(2019QZKK0703);中国地质科学院地质研究所基本科研业务费项目(YYWF201704,J1705);中国地质调查项目(DD20190060,DD20190370)。

摘　　要：早白垩世多尼组沿西藏北部班公湖—怒江缝合带沿线广泛分布,其沉积环境、碎屑组成和沉积物源等记录了班公湖—怒江特提斯洋闭合后拉萨—羌塘地体碰撞的演化历史。班戈地区多尼组以角度不整合于侏罗纪海相复理石之上,主要由砾岩、砂岩、粉砂岩、泥岩及少量安山岩夹层组成。砂岩中普遍发育槽状、板状、楔状交错层理,泥岩中可见泥裂,砾岩多为透镜状并发育叠瓦状构造,指示其形成于河流—三角洲沉积,且总体呈现出向上变粗的沉积组合序列。对多尼组中安山岩夹层样品进行LA⁃ICP⁃MS锆石U⁃Pb定年,获得206U/238Pb加权平均年龄为114±0.4 Ma。对砾岩中砾石成分和砂岩碎屑组成的统计分析结果显示,多尼组沉积组合中的碎屑组成主要来自蛇绿岩、中酸性岩浆岩、沉积岩和少量变质岩。砂岩重砂矿物组合和古水流分析结果表明,多尼组的沉积物源主要来自其南北两侧的拉萨和羌塘地体以及其下伏蛇绿岩。综合区域地质资料,班戈地区早白垩世多尼组是班公湖—怒江特提斯洋闭合过程中拉萨—羌塘地体碰撞背景下沉积作用的产物。The Lower Cretaceous Duoni Formation is widely distributed along the Bangong⁃Nujiang suture zone in northern Tibet.The sedimentary environment,clastic composition and sediment provenance records the Lhasa⁃Qiang⁃tang collision following the closure of the Bangong⁃Nujiang Tethys Ocean.The Duoni Formation in the Baingoin area angular⁃unconformably overlies Jurassic marine flysch deposits consisting of conglomerate,sandstone,siltstone and mudstone,with a minor andesite interlayer.Trough⁃,planar⁃and wedge⁃cross⁃beddings are common in the sandstone.Mudcracks are visible in the mudstone.The conglomerate is mostly lenticular with an imbricated structure,indicating that the Duoni Formation was formed in a fluvial⁃delta environment that shows a generally thickening⁃upwards se⁃quence.Zircon LA⁃ICP⁃MS U⁃Pb dating for the andesite interlayer sample obtained a 206U/238Pb weighted mean age of 114±0.4 Ma.Composition analysis of the conglomerate gravel and sandstone clastics shows that the provenance of the Duoni Formation was mainly from ophiolite,intermediate⁃felsic magmatic rock,sedimentary rock and a small amount of metamorphic rock.Analysis of detrital heavy mineral assemblage in the sandstones together with paleocur⁃rent analysis show that the sediment source areas of the Duoni Formation were the Lhasa and Qiangtang terranes on the northern and southern sides and its underlying ophiolite.Combined with regional geological data,the Lower Creta⁃ceous Duoni Formation in the Bangoin area is the product of the Lhasa⁃Qiangtang collision in the closure process of the Bangon⁃Nujiang Tethys Ocean.

关 键 词：多尼组 早白垩世 碎屑组成 班公湖—怒江缝合带 拉萨—羌塘地体碰撞 

分 类 号：P512.2[天文地球—地质学]