软碰撞、叠覆造山和多旋回缝合作用

软碰撞、叠覆造山和多旋回缝合作用^①

任纪舜　牛宝贵　刘志刚

摘　要　软碰撞是指陆块间，主要是微陆块间的弱碰撞。软碰撞后，陆块间尚未焊合，处于“联而不合”的状态。在新的构造阶段，这些陆块间又可再一次挤压和地壳缩短，发生大陆壳的消减造山作用，使一个大陆的大陆壳叠覆在另一个大陆的大陆壳之上，这就是陆陆叠覆造山作用。东亚诸陆块在古生代软碰撞后，曾长期处于“联而不合”的状态，只有再经过华力西、印支、燕山多旋回的陆陆叠覆和走滑挤压造山作用之后，它们才在动力学上最终焊合为一体，即经历了多旋回的缝合作用才合为一体。
关键词　软碰撞　叠覆造山　多旋回缝合作用
CLC　P542

SOFT COLLISION，SUPERPOSITION OROGENY AND POLYCYCLIC SUTURING

Ren Jishun　　Niu Baogui　　Liu Zhigang
(Institute of Geology，Chinese Academy of Geological Sciences，Beijing，10 0037)

Abstract　Microcontinents that constitute the present East Asian continent were part of th e interchange tectonic domain between Gondwana and Siberia (Laurasia) in the geo logical past. In Palaeozoic Era these small masses were mostly loca ted to the south of the palaeo-Asian ocean，belonging to the structurally compl icated northern margin of Gondwana; in Mesozoic Era they were mainly situated to the north of the Tethys，belonging to the structurally complicated southern mar gin of the palaeo-Asian continent (eastern Laurasia). In the course of the clos ure of the palaeo-Asian ocean the orogeny that happened there was not been a vi olent collision orogeny between the Gondwana and the Siberia continents proper b ut a slight or，say，soft collision between the microcontinents on their complic ated margins. Generally speaking，when microcontinents or small masses collid e with each other，the orogeny is usually slight because of lesser kinetic energ y. The tectonomagmatic activity is mainly restricted to the overthrusting contin ental crust，and the underthrusting one is only affected slightly. After collisi on，the oceanic basin disappears， but sea water does not definitely withdraw and mountains do not necessarily co me into being，leading to such collision that calls forth no response of mounta in building. Thus，the microcontinents，though being connected， are not to be j ointed into a single continent in dynamic respect，that is to say，they are in a state of "connection rather than integration". These non-united microcontinen ts may be subjected to another orogeny in a new tectonic cycle and new geodynami c conditions. The continental block lying in a low position will be again underthrust beneath the high mass，resulting in the subduction orogeny of continental crust，i.e.，the s uperposition of the margin of one continent upon that of another，which is calle d continental superposition orogeny. The continental masses can be geodynamical ly welded as a whole only after long-term and polycyclic continent-continent s uperposition or，say，polycyclic suturing. The welding process between the Sino -Korean block and the Yangtze block，which was accomplished not only by th e Caledonian collisional orogeny，but also by the Variscan，Indosinian and Yansh anian polycyclic superposition orogeny as well as the strike-slip-compressiona l orogeny，is an example of soft collision and polycyclic suturing.
Key words　soft collision，superposition orogeny，polycyclic sut uring

　　20世纪80年代，在进一步调查研究了中国东部地质之后，笔者指出，中国东部诸陆块间曾经历了长期的、多旋回的缝合过程，经历了由联而不合的碰撞—连接(碰接)到完全焊合为一体的聚合过程。中国东部的造山带并不是简单的碰撞造山带，而是多旋回复合造山带^［1］。在比较研究了中国与欧洲、北美的大地构造之后，笔者把巨型陆块间的强烈碰撞称之为硬碰撞，把微陆块间的微弱碰撞称为软碰撞^［2～5］。最近，随着1:500万中国及邻区大地构造图的出版，我们对微陆块的软碰撞和多旋回缝合作用又作了进一步的研究，现报道如下，敬希读者指正。

1　微陆和巨型大陆

　　中国所在的东亚大陆并不是以一个巨型前寒武纪克拉通为主体(如北美大陆以北美克拉通为其主体，欧洲大陆以俄罗斯(或东欧)克拉通为其主体)形成的单一大陆，而是由众多微陆和造山带组合而成的复合大陆。这些微陆以中朝、扬子、塔里木三个小克拉通面积最大，具有前震旦纪基底和发育良好的沉积盖层。中朝克拉通的面积大约是俄罗斯克拉通的1/5，北美克拉通的1/12.5；扬子克拉通大约是俄罗斯克拉通的1/7，北美克拉通的1/20。这些小克拉通，既具有克拉通的基本结构和特征，又有较大的构造活动性，所以黄汲清称为准地台。其它大量微陆，如图瓦-蒙古、中蒙古-额尔古纳、巴尔喀什-伊犁、准噶尔、布列亚-佳木斯、阿尔金、中祁连、若尔盖、中咱、羌塘、拉萨、中缅马苏等陆块，则均已较强烈地卷入显生宙的造山带，并成为其不可分割的一部分(图1)。