喜马拉雅前渊和孟加拉湾盆地形成演化

FORMATION AND EVOLUTION OF HIMALAYAN FOREDEEP AND BENGAL BAY BASIN

通过区域地质、地球物理、板块重建及地球动力学背景综合研究,揭示了喜马拉雅前渊和孟加拉湾盆地形成演化及动力学背景。喜马拉雅前渊与孟加拉湾盆地被西隆(Shillong)高原分隔。喜马拉雅前渊位于西隆高原北侧,主要以拉萨地块前白垩系为基底,晚白垩世—早始新世为新特提斯洋向洋内岛弧、拉萨板块俯冲形成的弧前和弧后盆地;中始新世—中新世早期,新特提斯洋逐渐俯冲消亡,印度板块与拉萨地块的陆陆碰撞逐渐加剧,形成前陆盆地;中新世中期以来,随着印度板块与欧亚板块陆陆碰撞的加剧,喜马拉雅前陆盆地隆升、剥蚀,只保留了前陆盆地的前渊。孟加拉湾(Bengal)盆地位于西隆高原南侧,其西北部以印度板块的前寒武系为基底,石炭—二叠纪为裂谷盆地,三叠纪为剥蚀区,侏罗纪—早白垩世以火山作用为主,晚白垩世—早始新世为被动大陆边缘盆地,中始新世以来随着印度板块向拉萨板块俯冲加剧,印度洋板块向缅甸大陆俯冲,孟加拉湾盆地演化为陆缘碎屑供应逐渐增强的残留洋盆。孟加拉湾东南部的基底为前古近系洋壳,始新世以来形成巨厚的残留洋盆充填序列。

The formation and evolution of the Himalayan foredeep and Bengal Bay Basin are carefully studied in this paper based on a comprehensive review of regional geology,geophysics,plate reconstruction and their geodynamic background.The Himalayan foredeep and the Bengal Bay Basin are separated by a high named the Shillong plateau.The former is located to the north of the plateau,with its basement dominated by the pre-Cretaceous Lhasa block.From Late Cretaceous to Early Eocene,it was a fore-arc and a back-arc basin resulted from subduction of the Neo-Tethys to the intra-ocean island arc and the Lhasa block.During the period from Middle Eocence to Early Miocene,the neo-Tethys subducted progressively and destructed finally,and the collision between the Indian plate and the Lhasa block was intensified gradually,and as the result,a foreland basin was formed.Since Middle Miocene,as the collision between the Indian plate and the Eurasian plate intensified,the Himalayan foreland basin experienced uplifting and denudation,and left behind a foredeep of the former foreland basin at last.The Bengal Bay Basin is located to the south of the Shillong plateau,the basement of its northwestern part is dominated by the pre-Cambrian of the Indian plate.From Carboniferous to Permian,it was a rift basin,and then denuded during Triassic.Volcanism dominated the Jurassic to Early Cretaceous.From Late Cretaceous to Early Eocene,it became a basin of passive continental margin.Since Middle Eocene,as the Indian plate intensively subducted under the Lhasa block and the Indian Ocean plate subducted under the Burma continent,the Bengal Bay Basin evolved into a residual ocean basin in which terrigenous clastic supply gradually increased.The basement of the southeastern part of the Bengal Bay Basin is dominated by pre-Paleogene oceanic crust,and the thick filling sequences of the residual oceanic basin has been formed since Eocene in the southeastern part of the basin.