西藏羌塘增生杂岩带内中—晚三叠世碳酸盐岩地层的发现及大地构造意义  

Discovery of the Middle-Late Triassic Carbonatite Formation in the Central Qiangtang Accretionary Complex,North Tibet and its Tectonic Siginifiance

作　　者：李林贵 梁晓[1] 王根厚[1] 王训练[1] 高曦 焦鹏伟[1] 黄祖根 LI Lingui;LIANG Xiao;WANG Genhou;WANG Xunlian;GAO Xi;JIAO Pengwei;HUANG Zugen(School of Earth Sciences and Resources, China University of Geosciences , Beij ing , 100083, China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地质学报》2018年第4期828-844,共17页Acta Geologica Sinica

基　　金：国家自然科学基金青年基金项目(编号41402177);中国地质调查局项目:"羌塘地体西侧及中央隆起带的综合地质调查"(子项目编码:12120115026901)联合资助的成果

摘　　要：羌塘中央增生(变质)杂岩带地层的解体有助于厘定龙木错—双湖缝合带和古特提斯洋俯冲-碰撞的时空演化过程。长期以来,该缝合带三叠纪地层研究薄弱,已有认识缺乏与洋陆俯冲古地理格局的联系。蓝岭高压变质带北侧3个露头中新发现一套中—晚三叠世台地相碳酸盐岩夹细碎屑岩、硅质岩沉积组合,它们以断块状叠置于中二叠世蛇绿混杂岩之上,内部层理近水平状,层序并未倒转,但顶底不全。依据岩性组合、相对层厚和化石分布,将层序较完整的西南侧岩块大致划分出三个沉积亚相:局限台地相、开阔台地相和台地边缘礁相。边缘礁相砾屑、生屑灰岩中含丰富的六射珊瑚化石,已鉴定出的珊瑚总计6属1种,分别为Conophyllia sp.,Omphalopylliasp.,Coryphylliasp.,Pamirastraeasp.,Margarophylliacf.capitata,和Craspedophylliasp.,指示地层时代为中三叠世拉丁期—晚三叠世诺利期。通过对羌塘盆地中—上三叠统的对比,发现北羌塘地体、中央增生杂岩带和南羌塘地体分别发育不同的沉积体系。构造接触关系及地层特征综合显示蓝岭北侧的中上三叠统代表北羌塘活动大陆边缘的弧前沉积,具体类型为增生楔上叠盆地。结合区域内中上三叠统的产出背景和生物化石时代,推测古特提斯洋闭合于晚三叠世诺利期中期。） accretionary complex（CQAC）provides important role in determining the temporal-spatial evolution of the Longmu Co-Shuanghu suture and the Paleo-Tethys Ocean.For a long time,however,the study of the Triassic strata in this area remains poor,particularly in lacking a correlation with the existing knowledge about the Triassic ocean-continent subduction/collision tectonics.Three outcrops on the north of Lanling were found to host one set of a Middle-Late Triassic platform-facies carbonatite intercalated with fine-grained clastic rocks and silicalite.They occur as brittle fault-bounded blocks and are superimposed on the Middle Permian ophiolitic mélange,with an approximately horizontal and un-inverted bedding,but its top and bottom are tectonically removed away.Based on the lithological assemblages,thickness variation of limestone layers and fossil distribution,three sedimentary subfacies were determined：restricted platform,open platform and shoal in the platform margin.The shoal facies bioclastic/intraclast limestones contain abundant hexacoralia fossils consisting of six genera including one species such as Conophyllia sp.,Omphalopyllia sp.,Coryphyllia sp.,Pamirastraeasp.,Margarophyllia cf.capitata,and Craspedophyllia sp.,which suggest an age of Ladinian of Middle Triassic-Norian of Late Triassic.A comparative analysis on the Middle-Upper Triassic strata of the Qiangtang basin shows different sedimentation systems occurring in North Qiangtan terrane,central accretionary complex（CQAC）,and South Qiangtan terrane.Both structural relationship and stratigraphic characteristics indicate that the newly discovered Middle-Upper Triassic carbonatite characterizes a portion of the fore-arc deposition in the active continental margin in south of North Qiangtang terrane,that is,slope basin immediately above the Triassic accretion wedge,which therefore implies a northward subduction polarity for the Paleo-Tethys Ocean.On the basis of tectonic background of the Middle-Upper Triassic in Central Qiangtang and time of t

关 键 词：羌塘 三叠纪 碳酸盐岩 珊瑚 古特提斯洋 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.245[天文地球—地质学]