羌塘盆地巴贡组构造-岩相古地理恢复

Structural,lithofacies,and paleogeographic restoration of the Bagong Formation in the Qiangtang Basin

羌塘盆地是我国重要的海相沉积盆地,具有广阔的矿产资源勘探前景。本文以野外实测剖面资料、区域地质调查数据、钻井信息为基础,结合地层学、岩石学、古生物学等方法,对羌塘盆地巴贡组沉积期古地理进行重建。以岩性组合特征、碳同位素偏移特征、古生物特征等方法建立巴贡组地层等时格架,发现日干配错组、菊花山组、土门格拉组、巴贡组、藏夏河组,苟鲁山克错组存在同期异相沉积。依据岩相组合和构造特征,发现羌塘盆地巴贡组时期存在三角洲相、滨岸相、潮坪相和陆棚相四种沉积环境。在沉积相的基础上探究巴贡组时期沉积演化,与区域构造背景结合,此时北羌塘盆地北部存在深水区,应为可可西里造山带与羌塘地块双向逆冲,地壳发生挠曲凹陷所致,形成弧后前陆盆地,南羌塘与班公湖-怒江洋盆接壤,为被动大陆边缘海盆,最后在上文的基础上进行成矿初步分析。

Qiangtang basin is an important marine sedimentary deposit in China,with broad prospects for mineral resources exploration.According to the field measured profile data,regional geological survey data and drilling data,combined with stratigraphy,petrology and paleontology,the paleogeography of Bagong Formation in Qiangtang Basin was restored.Based on the characteristics of lithologic association,carbon isotope migration and pale ontology,the isochronal framework of Bagong Formation is established.It is found that Rigan Mismatched Formation,Juhuashan Formation,TuPamela Formation,Bagong Formation,Cangxiahe Formation and Goulushan Kecuo Formation are heterogeneous deposits in the same time.According to lithofacies combination and structural characteristics,the Bagong Formation in Qiangtang Basin has four sedimentary environments:delta facies,coastal facies,tidal flat facies and shelf facies.On the basis of sedimentary facies,the sedimentary evolution of Bagong Formation was explored,combined with the regional tectonic background.At this time,the deep water area appeared in the northern part of the North Qiangtang Basin.Due to the two-way thrust of the Hoh Xil orogenic belt and Qiangtang block,the crust flexes and sags,forming a back-arc foreland basin,while the South Qiangtang basin is a passive continental margin basin bordering the Bangong Lake-Nujiang Ocean basin.Finally,on this basis,the mineralization is analyzed.