Sediment Provenance Analysis and Its Tectonic Significance in the Foreland Basin of the Ordos Southwestern Margin
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摘要: 前陆盆地充填沉积物中岩屑的分散形式和砂岩成分研究对确定物源区的逆冲事件、构造背景和与沉积物对应的物源层十分有效。通过对鄂尔多斯西南缘安口地区上三叠统沉积剖面系统采样测定发现，沉积物物源为一套变质碎屑岩和变质火山岩，为东祁连褶皱逆冲带中的陈家河组（Ｏ３ｃｈ）和葫芦河组（Ｚ－Ｏ２ｈｌ）。而西南缘千阳县上侏罗统砾岩物源为陇山群（Ｐｔ２ｌｎ）。上三叠统地层的物源分散形式为混合型，而上三叠统和上侏罗统两套地层统一的分散型式为倒序型，它是两期逆冲活动的沉积响应。根据鄂尔多斯西南缘安口地区上三叠统沉积物的ＱｍＦＬｔ端元成分作砂岩三角投影图，确定晚三叠世鄂尔多斯西南缘盆地性质为发育于碰撞造山带之前陆的前陆盆地。其物源为再旋回活动的褶皱逆冲断块。Abstract: It is effective to determine thrust events of provenance, tectonic setting and provenance strata cor re-sponding to basin sediments according to the clast dispersal style and the components of sediments inforeland basins. Test and study on the Upper Triassic stratigraphic section of the Ankou region in thesouthwestern margin of Ordos show that the provenanc es of stratigraphy are a set of meta lastics andmeta}olcanics which are Chenjiahe Formation(O3ch)and Huluhe Formation(Z- O2hl)〔ontributed inteh eastern Qilian fold-thrust belt. The provenance of the Upper Jurassic conglomerate in the south-western margin is Longshan Formation(Pt2ln)·The dispersal style of the Upper Triassic is the blended clast composition, and thedispersal style of the both of the Upper Triassic and the Upper Jurassic is theinverted dust composition which is the sedimentary response to two times of large thrusting. The analy-sis on the QmFLt triangular diagram representing the sandstone components of the Upper Triassic in theAnkou region shows that the Late Triassic basin in the southwestern margin of Ordos is a foreland basinlocated in the foreland of a collision orogen and the provenance is the fold-thrust massif of the recycledo rogen which is the eastern Qilian orogen.
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Key words:
- foreland basin /
- dispersal style /
- the Qm FLt triangular diagram
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