原特提斯北界西段构造演化与拼合方式

发布时间：2019-03-13 16:25

【摘要】：原特提斯洋是从Rodinia裂解到早古生代末发育于滇缅泰/保山微陆块以北、塔里木-华北陆块以南的一个复杂大洋。原特提斯洋内存在中祁连、柴达木、扬子、华夏、印支、兰坪-思茅等诸多陆块/微陆块，在其东亚范围内西北部早古生代末发育有北祁连、柴北缘等一系列蛇绿岩带或高压-超高压变质带。这些地质记录表明早古生代期间原特提斯洋经历了复杂的洋-陆格局和聚散过程。但至今原特提斯洋的边界、不同陆块/微陆块属性和关系及其在早古生代末与北方大陆的拼合过程还存在争论，而这是恢复重建Pangea超大陆聚合前期早古生代构造背景的关键。针对这个关键科学问题，本文将采用野外地质调查、构造、岩浆、沉积学、地球化学、构造年代学等手段，对原特提斯域西北部进行以下三方面的研究：（1）界定原特提斯域的北部西段边界；（2）建立原特提斯洋北部陆块/微陆块的亲缘性和海-陆格局；（3）厘定原特提斯北部微陆块拼合时序与方式。通过综合集成研究，得出以下几点新认识： 1、原特提斯洋经历了多岛洋和微陆块拼合的复杂构造格局演化过程，且洋盆的打开和闭合均具有穿时性。根据蛇绿岩的对比，发现祁连洋向西延至北阿尔金洋，南祁连洋向西延至南阿尔金洋，具有东早西晚的剪刀式打开方式；根据榴辉岩形成时间对比，原特提斯洋具有从西向东斜向闭合的特点，符合“剪刀式”的拼合模式。 2、根据榴辉岩折返时间，南祁连洋早期向南俯冲，最终闭合（460~420Ma），原特提斯洋北界仍在北祁连洋；南祁连洋盆闭合后，昆南洋闭合（428Ma），最后祁连洋洋盆闭合（420~410Ma），原特提斯洋北界一直为北祁连地区。 3、原特提斯洋的演化可简单的概括为Gondwana裂解期间，众多地块从Gondwana裂离并向北先后拼合的过程。震旦纪-早中寒武世期间塔里木是亲扬子的，阿拉善新元古代-早古生代亲华北，总之各个微陆块与华北陆块和扬子陆块的亲缘性是随时间变化。 4、结合野外地质、构造变形和年代学资料以及岛弧岩浆岩、沉积建造分布特点，本文认为北祁连向南俯冲，南祁连洋为其弧后，裂解形成洋壳，存在时间非常短；昆南洋俯冲比北祁连稍晚，，向北俯冲形成昆中弧后盆地，发育至早古生代末转变为昆中洋盆，并开始向北俯冲，形成祁曼塔格弧后盆地。
[Abstract]:The original Tethys Ocean is a complex ocean from Rodinia cracking to the end of early Paleozoic to the north of the Yunnan-Myanmar-Thailand / Baoshan microcontinental block and to the south of the Tarim-North China continental block. In the original Tethys Ocean, there are many continental blocks / microcontinental blocks such as Qilian, Qaidam, Yangzi, Huaxia, Indosinian, Lanping-Simao and so on. North Qilian developed at the end of the early Paleozoic in the northwest of the Tethys Ocean. The northern margin of Qaidam is a series of ophiolite belt or high-pressure-ultra-high pressure metamorphic zone. These geological records indicate that the original Tethys Ocean experienced a complex ocean-land pattern and dispersion process during the early Paleozoic. But up to now, the boundary of the original Tethys Ocean, the attributes and relations of different continental blocks / microblocks and their assembling process with the northern continent at the end of the early Paleozoic are still controversial, which is the key to the restoration and reconstruction of the early Paleozoic tectonic background of the Pangea supercontinent in the early stage of aggregation. In view of this key scientific problem, this paper will adopt the methods of field geological survey, tectonics, magma, sedimentology, geochemistry, tectonic chronology and so on. The following three aspects are studied in the northwest of the original Tethys region: (1) to define the western border of the northern part of the original Tethys region; (2) to establish the affinity and sea-land pattern of the northern part of the original Tethys Ocean; (3) to determine the timing and mode of the combination of the micro-land blocks in the northern part of the original Tethys. Through the comprehensive integration study, the following new understandings are drawn: 1. The original Tethys Ocean experienced the complex tectonic framework evolution process of the multi-island ocean and the micro-continental block, and the opening and closing of the ocean basin were transitory. According to the comparison of ophiolite, it is found that the Qilian Ocean extends westward to the North Altun Ocean, and the South Qilian Ocean extends westward to the South Altun Ocean. According to the comparison of eclogite formation time, the original Tethys Ocean has the characteristics of oblique closure from west to east, which is in accordance with the "scissors" pattern. (2) according to the eclogite exhumation time, the South Qilian Ocean subducted southward and finally closed (460~420Ma) in the early stage of the South Qilian Ocean, and the original Tethys northward boundary was still in the North Qilian Ocean; After the closure of the South Qilian basin, the Kunnan Ocean closure (428Ma), and finally the Qilian Ocean Basin closure (420~410Ma), the former Tethys northward boundary has always been the North Qilian region. 3. The evolution of the original Tethys Ocean can be simply summarized as the process during the Gondwana cracking, during which many parcels split from Gondwana and coalesced northward. During the Sinian-early Middle Cambrian period, Tarim was Yangtze-friendly, and Alxa Neoproterozoic-early Paleozoic was pro-North China. In a word, the affinity between each microcontinent block, North China continent block and Yangtze continent block changed with time. 4. Combining the data of field geology, tectonic deformation and chronology as well as the distribution characteristics of island arc magmatic rocks and sedimentary formations, it is considered that the North Qilian subducted southward, and the South Qilian Ocean was its back arc, and the oceanic crust was formed by splitting and forming the oceanic crust, which existed for a very short time. The subduction of the Kunnan Ocean is a little later than that of the North Qilian. The northward subduction of the Kunnan Ocean formed a back-arc basin in Kunzhong, which developed to the end of the early Paleozoic and began to submerge northward to form a back-arc basin of Qimantag.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P736.22

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