鄂尔多斯盆地西缘中—晚三叠世构造-物源-古地貌体系演化——来自碎屑锆石、地球化学和岩石学的证据

Tectonics-provenance-palaeogeomorphology system evolution of the western margin of Ordos Basin during the Middle-Late Triassic:the evidences from U-Pb detrital zircon geochronology,geochemistry and petrology

构造-物源-古地貌体系研究是明确盆地演化的重要手段,是油气资源潜力精确评价的基础。鄂尔多斯盆地西缘中—晚三叠世存在物源、古地貌不清的问题。利用碎屑锆石测年、地球化学等方法对鄂尔多斯盆地西缘及邻区中—晚三叠世开展了构造、物源、古地貌系统分析。研究结果表明:中三叠世时河西走廊和鄂尔多斯盆地西缘有统一物源;晚三叠世时物源差别很大,河西走廊物源来自于祁连和柴达木地块,盆地西部物源则来自于西华北地块。物源分析结果结合地层对比和岩石学、地球化学数据表明中三叠世晚期河西走廊和鄂尔多斯盆地有短暂沟通,晚三叠世时存在分隔两地的小规模水下古隆起。这种物源和古地貌演化与华北—扬子板块在中—晚三叠世的自东向西碰撞过程相适应,反映了挤压主应力点西移的事实以及在此背景下盆内由挠曲向抬升的地貌演化过程。

The study of tectonics-provenance-paleogeomorphology system is an important means to clarify the basin evolution,providing a basis for accurately evaluating the oil and gas potential.The provenance and paleogeomorphology of the western margin of Ordos Basin in the Middle-Late Triassic are not clear.Using detrital zircon geochronology and geochemistry methods,this study analyzes the tectonics-provenance-paleogeomorphology system in the western margin of Ordos Basin during the Middle-Late Triassic.The results show that the Hexi Corridor and the western margin of Ordos Basin had the same provenance during the Middle Triassic,while greatly different in the Late Triassic.The provenances in Hexi Corridor and the western margin of Ordos Basin were sourced from Qilian-Qaidam Block and West North China Block,respectively.Based on the provenance analysis results in combination with stratigraphic correlation as well as petrological and geochemistry data,it is proven that the Hexi Corridor and Ordos Basin were connected temporarily in the late period of Middle Triassic,and a small-scale underwater paleo-uplift in two separate places existed in the Late Triassic.The evolution of provenance and paleogeomorphology corresponded to the Middle-Late Triassic east-west collision of North China-Yangtze Plate,thus reflecting the primary stress point moving westward and the geomorphologic evolution process from flexure to uplift.