贺兰山及周边地区加里东运动研究

基于对贺兰山及周边地区下古生界详细的野外地质调查,通过碎屑锆石年龄谱的物源分析、地层接触关系追踪、岩性岩相突变特征分析、残留地层分布、古生物组合及亲缘性分析,讨论了阿拉善地块与华北地块和中祁连地块的亲缘关系,探讨了研究区加里东运动的幕次,认为早古生代阿拉善地块和华北地块相互独立,俯冲造山特征建造不清晰,两者之间可能为转换型陆缘。阿拉善地块和中祁连地块之间的加里东运动幕次清晰。加里东运动一幕发生在中-晚寒武世,香山群深水复理石沉积和张夏组浅水碳酸盐台地相沉积呈拼合式接触,生物组合为亲华北-亲祁连混合型,彼时中祁连地块从Rodinia大陆裂离,逐步靠近阿拉善地块;加里东运动二幕发生在早-中奥陶世,下奥陶统碳酸盐岩在全区稳定分布,与下伏香山群不整合接触,与阿不且亥组整合接触,生物相统一,生物组合为华北型,中祁连地块-阿拉善地块-华北地块平和成为一个统一的块体,整体为浅水台地沉积环境;加里东运动三幕发生在奥陶纪末,中-上奥陶统与泥盆系角度不整合接触,商丹洋闭合,扬子地块与阿拉善地块和华北地块靠近,商丹缝合带南部的宽坪洋打开,导致研究区中、晚奥陶世亲华北-亲扬子混合型生物组合类型。

Study on Caledonian Movement in Helanshan and its surrounding area

Based on the field geological investigation of Lower Paleozoic in the Helanshan and its surroundings area, we discuss the provenance of the Xiangshan Group through analysis of detrital zircon age, study the stratigraphic contact relationship of Lower Paleozoic of the different stratigraphy area in the Helanshan and analyze the lithofacies mutation features and explore paleontological and affinity. The aim of the work is to study the continental affinity among Alex Block, North China Block and Central Qilian Block and probe the Caledonian Movement phases in research area. Caledonian Movement phases between Alax Block and North China Block is unclear. There may be a transform boundary between the two blocks because of the lack of subduction orogenic characteristics. Caledonian Movement phases between Alax Block and Central Qilian Block are clear. The first phase of Caledonian Movement occurred in Mid-Late Cambrian. Xiangshan Group which is flysch facies in Qilian stratigraphy province has a collage-like contact with Zhangxia Formation which is shallow water carbonate platform in Alax stratigraphy province. The biological assemblage belongs to North China-Qilian type in Mid-Late Cambriam. Qilian block is separated from Rodinia and gradually close to Alax Block at that time. The second phase of Caledonian Movement occurred in Early-Middle Ordovician. The carbonate rocks of Tianjingshan Formation stably distribute all over the region, which has an unconformable contact with underlying Xiangshan Group, and has a conform contact with underlying Abuqiehai Formation. The bio-facies are unified, and the biological assemblage is North China type in Early-Middle Ordovician. The Central Qilian Block, Alax Block and North China Block combined in Early-Middle Ordovician which has the same bio-facies and shallow water platform sedimentary facies. The third phase of Caledonian Movement happened in the end of Ordovician. The Middle-Upper Ordovician has an unconformable contact with Devonian. Proto-Tethys Shangdan Ocean is closed while Yangtze Block is close to North China Block and Alax Block. Kuanping Ocean in south of Shangdan Suture Zone open so the biological assemblage belong to North China-Yangtze paleontology assemblage during Middle-Upper Ordovician. Alax Block and North China Block are separate plates in Cambrian.