复合造山作用和中国中央造山带的科学问题

Compound orogeny and scientific problems concerning the Central Orogenic Belt of China

在全球大陆范围内,广泛分布的造山带纪录了板块汇聚的历史和碰撞造山的过程,因此,造山带的研究一直是地球科学经久不衰的重要领域。研究表明,世界上许多造山带是长期活动(>300Ma)的复合造山带,活动域的宽度可超过1000km,并具有造山前的热结构,是大陆生长的最好见证。近10年来,全球造山带的研究已摆脱传统地质学和经典板块观念的束缚,面临一个新的起点,即由单一造山带向复合造山带研究转轨,由造山类型、造山作用向造山动力学研究聚焦。复合造山带长期活动的原因、大陆增生机制、造山带的流变学结构和造山热对造山作用的控制等已成为当前大陆复合造山带研究的关键科学问题,复合造山动力学已成为当今地球科学前沿——大陆动力学研究的重要内容。中国中央造山带位于北中国板块与南中国板块之间,是中国大陆上一条十分醒目而又极其重要的巨型(长5000km)构造带。中央造山带是经历了大致600Ma的活动历史,泥盆纪和三叠纪的两次碰撞造山以及白垩纪以来的陆内造山过程而构筑成的典型"复合造山带"。在全球复合造山带中,中国中央巨型造山带具有结构复杂性、活动长期性和非原地型,造山过程多期性以及造山带拼贴与大陆增生方式特殊性的特点,特别是世界最大规模的中央超高压变质带及其两期超高压变质作用的发现,揭示了中央造山带的形成还经历了板块汇聚边界洋壳/陆壳深俯冲至100km以上的地幔深处的两次壮观地质事件,使中央造山带成为全球造山带中最为精彩和不可多得的典型,与青藏高原一样,被国内外地学家们誉为当今中国地学研究的"瑰宝"。中国中央巨型复合造山带可以作为研究复合造山过程与复合造山动力学的重大地学问题的范例,重要的核心科学问题是:中国中央巨型复合造山带的早古生代和三叠纪陆块汇聚、碰撞造山过程以及中新生代陆内造山与周缘盆地互馈;两期高压-超高压变质带的时空关系、形成条件和洋壳/陆壳的俯冲-深俯冲与折返动力学机制;揭示和探讨中国中央复合造山带的长期活动性,造山作用的多期性和叠置性,造山热结构以及复合造山过程;洋壳/陆壳深俯冲、复合造山与大陆增生理论的创新。此外,中央复合造山带的研究对于金属矿产资源的开拓、周缘中新生代盆地含油气资源的战略前景以及现今南北中国的气候、环境、人文、地理、生态和灾害的制约提供新的科学依据与动力学背景。

Orogenic belts widely distributed in the Earth have recorded the history of plate convergence and orogenic processes during the collision.Many of these belts are long-lived（300 Ma） compound belts,which are more than 1000 km wide with a pre-orogenic thermal structure that provides evidence for continental growth.In the past decade,research has begun to focus on the long-term dynamics of such belts as well as their tectonic features and processes.A number of critical problems remain existent,which include the origins of the longterm activities,the mechanism of continental accretion,and the rheological and thermal structure of such orogens.The Central Orogenic Belt of China（COB） is a huge compound orogen,which extends more than 5000 km across central China and marks the boundary between the North China Block and the South China Block.The COB has been active for ～600 Ma,and during this time it underwent two major collisions,one in the Devonian and the other in the Triassic.In addition,the region has become tectonically active since the Cretaceous.The COB differs from other compound orogens in having a very complex structure,multiple long-term orogenic events,convergence of orogens and accretion of continents.The recent discovery of a large high-and ultrahighpressure metamorphic belt（HP-UHP） in the orogen and the recognition of two HP-UHP metamorphic events indicate the subduction of both oceanic and continental crust to the depth greater than 100 km.Thus,the COB is as important in the tectonic evolution of Asia as the Qinghai-Tibetan Plateau.Some of the critical unanswered questions regarding the COB include the nature of the continental convergence,collision and orogeny in the Devonian and Triassic and the formation of intracontinental sedimentary basins during the Mesozoic and Cenozoic.Also unclear are the temporal and spatial relationships of the HP-UHP metamorphic belts and the conditions under which deep subduction and exhumation of oceanic/ continental crust took place.Likewise,the processes responsible for the long-term tectonic activity,the multiple and overlapping orogenies,and the thermal structure of the region are unclear.In addition,little is known about the genesis of the mineral deposits in the region and the oil and gas potential of adjacent Mesozoic and Cenozoic basins.