苏峪口寒武纪-三叠纪沉积演化及其对阿拉善-华北构造关系约束

It has been a hot topic whether Alxa block is an extension to the west of North China Craton for a very long time. Some researchers believe that Helan Tectonic Belt or its adjacent fault zone is the tectonic boundary separating Alxa block and North China Craton, however, whether Helan Tectonic Belt can be treated as a plate boundary, its tectonic attribution and mountain-basin evolution are still debated. Methods such as stratigraphy, sedimentology, source tracing and basin analysis are applied in this project to investigate Cambrian-Triassic outcrops in Suyukou systematically. Basic geological characteristics of Cambrian to Triassic of Helan Tectonic Belt, such as tecto-stratigraphic system, sedimentary features, provenance of materials, will be ascertained firstly, and then to be contrasted with those of surrounding tectonic units. Combined with regional tectonic background, we will rebuild basin-range system, illuminate the location of source-sink, basin type, tectonic setting of provenance region and evolution laws of different stages from Cambrian to Triassic of Helan Tectonic Belt and adjacent area. Furthermore, we will discuss tectonic-sedimentary coupling relationship of Helan Tectonic Belt and its adjacent area in different stage, to find out if it can be treated as the tectonic boundary of North China Craton and Alxa block. Our study will be helpful to understand Cambrian-Triassic tectonical attribute and basin range transition of Helan Tectonic Belt, and the connection between Alxa block and North China Craton.

阿拉善地块是否是华北克拉通的西延一直是地学界的关注热点，部分学者认为贺兰构造带或其周边断裂带是分隔阿拉善地块与华北克拉通的构造界限，然而贺兰构造带能否构成板块界限、其构造属性和盆山演化仍存在极大争议。本项目拟运用地层学、沉积学、物源示踪、盆地分析等理论与手段，对苏峪口地区出露的寒武系-三叠系进行系统的野外地质调查。查明贺兰构造带寒武系-三叠系构造-地层系统、沉积特征、物质来源等基本地质特征，并与周边构造单元进行对比。结合区域构造背景，重建贺兰构造带周缘寒武纪-三叠纪不同阶段盆山系统，阐明源-汇位置、盆地性质、源区构造环境与演化规律。进一步探讨贺兰构造带与周边地质单元不同阶段的构造-沉积耦合关系，明确贺兰构造带和其两侧构造单元所处的构造位置以及是否构成分隔华北与阿拉善的板块界限。本研究的开展将提高对贺兰构造带寒武纪-三叠纪构造属性及盆山转换的认识，有助于了解阿拉善与华北的构造转接关系。

华北克拉通向西的岩石是一个新的研究热点。关于华北克拉通西部的的鄂尔多斯地块和阿拉善地块的拼合时限和板块边界存在诸多不同的观点。越来越多的学者趋向于认为阿拉善和华北克拉通在奥陶纪、甚至三叠纪之前是独立的块体。但区域地质调查结果表明，贺兰山构造带及其周缘的构造、岩浆和变质证据无法证明阿拉善和鄂尔多斯地块在显生宙发生过碰撞。本次研究对贺兰山及其周缘盆地内的寒武系-三叠系开展地层和沉积研究。.巴彦浩特盆地、贺兰山构造带及鄂尔多斯盆地古生界地层序列、岩石组合是相似的。这些海相地层中所包含的古生物化石群落是和华北克拉通东部的同时期地层一致，证明他们处于相同古生态系统。贺兰山构造带内寒武系-三叠系砂岩样品与其两侧巴彦浩特盆地、鄂尔多斯盆地西北部同一时期的样品具有相同的碎屑锆石年代学曲线。这证明，寒武纪-三叠纪不同阶段，整个华北克拉通西部的沉积岩具有相同的物源体系、沉积盆地是连通的。.寒武纪至奥陶纪华北克拉通西部的沉积盆地演化是对古亚洲洋向阿拉善地块之下推进型俯冲演化的沉积响应。该转换造成了阿拉善地区在挤压大地构造背景下发育安第斯型大陆岛弧以及与之成对的弧后前陆盆地。华北克拉通西部从被动大陆边缘盆地向前陆盆地的构造转换被约束在了~ 467 Ma，在西部的贺兰山和巴彦浩特盆地前渊地带造成了向东的砂质复理石的推进，在东部的鄂尔多斯前陆远端地带造成了碳酸盐岩台地的沉没以及向东的深水盆地推进。在石炭纪-二叠纪，鄂尔多斯西北部则发育弧后盆地，其演化与华北北部的安第斯岛弧密切相关。随后的再次沉降在贺兰山构造带内构成了三叠系地层楔，该地层楔由向东南流动-加深的河湖相沉积体系构成，但是其内部的地层则向北西加厚。该地层楔被解释为不对称裂谷盆地的沉积充填结果，与古亚洲洋闭合后造山带的垮塌有关。.整个鄂尔多斯西北部寒武纪-三叠纪具有连通的源汇体系和密切相关的动力学环境。这表明阿拉善地块在显生宙早期已经是华北克拉通西部的一部分。