晚中新世以来孟加拉-尼科巴扇跷跷板式沉积转换及其源-汇成因机制  

Depositional patterns of the Bengal-Nicobar Fan system since the Late Miocene:Seesaw-like stepwise changes and the source-sink model

作　　者：龚承林[1,2] 刘力 邵大力 郭荣涛 朱一杰 齐昆 GONG Chenglin;LIU Li;SHAO Dali;GUO Rongtao;ZHU Yijie;QI Kun(State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum(Beijing),Beijing 102249,China;College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China;State Key Laboratory of Geological Processes and Mineral Resources,Institute of Earth Sciences,China University of Geosciences(Beijing),Beijing 100083,China;PetroChina Hangzhou Research Institute of Geology,Hangzhou 310023,China;Sinopec Petroleum Exploration&Production Research Institute,Beijing 100083,China)

机构地区：[1]油气资源与探测国家重点实验室(中国石油大学(北京)),北京102249 [2]中国石油大学(北京)地球科学学院,北京102249 [3]中国地质大学(北京)科学研究院地质过程与矿产资源国家重点实验室,北京100083 [4]中国石油杭州地质研究院,浙江杭州310023 [5]中国石化石油勘探开发研究院,北京100083

出　　处：《地学前缘》2022年第4期25-41,共17页Earth Science Frontiers

基　　金：国家自然科学基金项目(41972100,41802117);中国石油大学(北京)地球科学学院优秀青年创新团队项目(2462020YXZZ020)。

摘　　要：利用沉积转换事件再造关键变革期的构造活动和气候演变是源-汇系统研究的新动向和切入点。新生代以来,印度大陆与亚洲大陆的汇聚隆升以及喜马拉雅-青藏高原的剥蚀、向孟加拉湾的物质输入,形成了当今世界上最大的源-汇系统(喜马拉雅-孟加拉湾源-汇系统)。利用3D地震数据和IODP 354与362航次获取的碎屑锆石数据揭示了晚中新世以来孟加拉-尼科巴扇沉积转换事件及其源-汇成因机制。研究认为尼科巴扇和孟加拉扇经历了此消彼长的沉积建造过程:尼科巴扇经历了“晚中新世快速进积→上新世缓慢建造→第四纪相对静止”的建造过程;而孟加拉扇经历了“晚中新世相对静止→上新世缓慢建造→第四纪快速进积”的沉积建造过程。喜马拉雅-孟加拉湾源-汇系统碎屑锆石年龄核密度统计结果显示:晚中新世以来,指示古布拉马普特拉河迁移演化路径的60~0 Ma碎屑锆石在若开-尼科巴扇呈现出逐渐减少的变化趋势,而在孟加拉扇呈现出逐渐增多的变化趋势。这一碎屑锆石年龄核密度变化特征表明:(1)在晚中新世,古布拉马普特拉河主沉积物分散路径靠近孟加拉湾东部一侧发育且大量碎屑颗粒向尼科巴扇搬运分散,形成“快速进积的尼科巴扇和相对静止的孟加拉扇”;(2)在上新世初,青藏高原隆升所诱发的西隆高原抬升使古布拉马普特拉河向西迁移分流,在古西隆高原北缘Mikir山附近分流为东西两支,东支向尼科巴扇搬运分散的碎屑颗粒开始减少,而西支向孟加拉扇搬运分散的碎屑颗粒开始增多,形成“以缓慢建造为演化特征的尼科巴-孟加拉扇”;(3)在第四纪初,印度板块-亚洲板块最强碰撞造成青藏高原最强隆升并达到最大海拔高度,古布拉马普特拉河东支袭夺废弃,向尼科巴扇卸载的沉积物相应显著减少,而古布拉马普特拉河西支与恒河并流后向孟加拉扇卸载的�Tectonic and climate reconstruction based on punctuated,abrupt changes in depositional patterns represents a new research focus in source-sink analysis.Since the Cenozoic,the convergence of the India and Asian plates,and the subsequent Himalayan exhumation,erosion and sediment transport to the Bengal Bay,formed the world largest source-sink system.Our current study mainly employed 3D seismic and detrital zircon U-Pb age data to address the punctuated,abrupt changes in the depositional patterns of the Bengal-Nicobar Fan system since the Late Miocene,and explore the genetic mechanism of these changes according to the source-sink model.Our findings suggest a seesaw-like stepwise evolution and development of the Bengal-Nicobar Fan system.The Nicobar Fan experienced progradation in the Late Miocene,slow growth in the Pliocene and dormant growth in the Quaternary,which run opposite to the evolution of the Bengal Fan.The U-Pb detrital zircon chronology of the Himalayan-Bengal source-sink system by normalized kernel-density estimates suggest that since the Late Miocene,the 60-0 Ma zircon age populations(indicative of the Brahmaputra sediment routing system)progressively decreased in the Rakhine-Nicobar Fan while increased gradually in the Bengal Fan,revealing an overall stepwise evolutionary pattern of the Brahmaputra sediment routing system.In the Late Miocene,the Brahmaputra River with robust delivery capacity developed along the eastern Bengal Bay delivering large volume of clastic detritus into the Nicobar Fan;whereas the Tista and Ganges Rivers with low delivery capacity developed along the western Bengal Bay transporting small volume of detrital sediments into the Bengal Fan.Such a sediment routing system fostered progradation in the Nicobar Fan and dormant growth in the Bengal Fan.In the Pliocene,the uplift of the Shillong Plateau led to divergence of the Brahmaputra River into eastern and western tributaries.The eastern Brahmaputra tributary with deceased delivery capacity delivered less clastic detritus into the

关 键 词：源-汇系统 孟加拉-尼科巴扇 沉积转换事件 青藏高原隆升 布拉马普特拉河 

分 类 号：P542[天文地球—构造地质学] P512.2[天文地球—地质学] X14[环境科学与工程—环境科学]