扬子、华夏古板块会聚带在湖南的位置

扬子、华夏板块会聚带在湖南的位置一直是地学界关注的热点和争论的焦点,但始终未能取得共识.确定扬子、华夏板块会聚带在湖南的位置,弄清板块结合带在湖南的走向,对于华南大地构造划分和基础地质理论研究具有重要意义.由于缺乏地表直接地质证据,因此深部地球物理资料将成为探讨板块结合带走向的重要依据.本文结合地质资料,利用区域重磁、地震、大地电磁测深、地热流等提供的深部构造地球物理信息标志,对湖南及周边华南地区岩石圈三维结构特征进行了重新认识和地质解释,对扬子-华夏板块结合带的构造性质、在湖南的位置以及江南古陆构造属性等提出了新认识.在江南古陆中段的湖南沅(江)麻(阳)-洞庭-衡阳弧形重力高主要为古火山锥型结晶基底隆起引起,在麻阳、桃源、益阳-南桥一线构成古火山岛链;推断在浏阳-衡阳一带存在湘东残剩隐伏古火山岛.首次厘定了扬子、华夏残剩古板块上地幔刚性块体的空间分布形态,在此基础上推测其间的过渡带属赣湘桂古华南洋.提出新元古代造山带属陆-弧-岛-陆碰撞造山带,陆间湘东残剩隐伏古火山岛成为现今板块融合带的组成部分,扬子、华夏古板块及其间的过渡带三者岩石圈上地幔纵横向三维结构特征完全不同.论证了赣湘桂中部岩石圈古俯冲带的存在,再次确定湘中地区岩石圈厚度在华南最厚.厘定扬子、华夏古板块深部结合带北西边界大致在安徽歙县-南昌-湖南大围山-沩山-城步-广西河池一线,结合带南东边界大致在江山-绍兴-新余-萍乡-衡东-双牌-桂林-柳州一线,两板块之间的中间融合带就是所谓"钦杭结合带"在湖南的位置,过去地学界较普遍认可的茶陵-郴州断裂,我们认为不是扬子板块与华夏板块的会聚带,而是华夏板块板内加里东期仰冲断裂带.

Location of the Yangtze-Cathaysia plate convergence zone in Hunan

Location of the Yangtze-Cathaysia plate convergence zone in Hunan is concerned by investigators and has not coincident recognition for absence of direct evidence.Certainty of the location and trend of the Yangtze-Cathaysia plate convergence zone in Hunan has scientific significance to the tectonic division of South China and basic geology theory.Geophysical features of deep structures turn into essential foundation in certaining location of the plate convergence zone for absence of upper direct evidence.Combined with geological data,using deep structure informations provided by regional gravity and magnetic,seismic,magnetotelluric sounding and heat flow data,this paper reinterprets 3D lithospheric structure of Hunan and South China,and brings new knowledge the tectonic characteristics and the location of the Yangtze-Cathaysia plate convergence zone in Hunan,and about the tectonic characteristics of Jiangnan ancient land.The study consider that the YuanMa-Dongting-Hengyang arc gravitational high is caused by crystalline basemental uplift with paleo-volcanic cone,and infer that there exist paleo-volcanic island-chain along Mayang-Taoyuan-Yiyang-Nanqiao,and hidden residue paleo-volcanic islands along Liuyang-Hengyang,east Hunan.The authors drew the shape of the rigid upper mantle block of Yangtze and Cathaysia paleo-plate;conferred that the Yangtze-Cathaysia intermediate zone were paleo-Jiangxi-Hunan-Guangxi south-China ocean.The paper brings forward recognitions as follow: the Neoproterozoic orogenic belt was continent-arc-island-continent collision orogenic belt;intercontinental hidden residue paleo-volcanic islands in south Hunan are nowadays part of plate merge belt;3D Lithospheric structural characteristics of Yangtze,Cathaysia block and intermediate zone are absolutely different;there existed paleo-lithospheric subduction zone in middle Jiangxi-Hunan-Guangxi;the lithosphere of middle Hunan is thickest in South China;the northwestern boundary of Yangtze-Cathaysia plate convergence zone was along Xixian-Nanchang-Daweishan-Weishan-Chengbu-Hechi,while the southeastern boundary along Jiangshan-Shaoxing-Xinyu-Pingxiang-Hengdong-Shuangpai-Guilin-Liuzou;plate merge belt between Yangtze and Cathaysia plate are the Qinzhou-Hangzhou juncture in Hunan.Chaling-Chenzhou fault wasn′t the Yangtze-Cathaysia plate convergence zone but Caledonian intraplate thrust fault in Cathaysia plate.