贺西地区中-晚古生代盆地性质刍议

贺西地区处于北祁连加里东褶皱带、阿拉善地块与鄂尔多斯地块的交汇处,多期构造活动造就了本区复杂的构造和成盆历史。该区晚古生代早中期处于早古生代洋盆体制与中生代陆内盆地发育期的转换时期,对该时期盆地的性质及其成因争议颇多。本文通过贺西地区晚泥盆世和早中石炭世同沉积正断层及其相关地质现象的论述并结合前人的研究成果,对贺西地区晚古生代早期盆地的性质及其成因进行了讨论,认为该期盆地既非碰撞裂谷,也非前陆盆地,而是造山后伸展型上叠盆地,同时认为该伸展盆地的形成与古特提斯洋等的形成具有一定的同步性,具有一定的区域地质意义。该区石炭系烃源岩条件良好,东部地区是油气勘探的有利区。

COMPARATIVE STUDY ON THE CHARACTERISTICS OF THE MID-LATE PALEOZOIC BASINS IN HEXI AREA

The Hexi area is located at the tectonic convergence of the North China block and north Qilian Caledonian orogen and Alex block, and is characterized by multiple tectonism that resulted in very rich and complicated geological phenomena. In the area, the mid-late Paleozoic is the transitional period between the early Paleozoic oceanic stage and the Mesozoic continental basin developing stage, and many controversial explanations have been proposed regarding the formation mechanism of the mid-late Paleozoic basins. From field work, synsedimentary normal faults have been found in the upper Devonian and Carboniferous in many places of Hexi area. On the basis of the field work in combination with the former studies, the authors discussed the characters and formation mechanism of the Hexi mid-late Paleozoic basins. Here we propose that the basins are neither foreland basins nor impactogen, but are extensional superimposed basins resulted from detachment of the north Qilian Caledonian orogenic belt, and the basin formation is simultaneous with the opening of Mianlue ocean, Changning-Menlian ocean etc., and with the early evolution stage of the Paleo-Tethys, and all these suggest that the formation of the mid-late Paleozoic extensional superimposed basins in the Hexi area is significant to the regional geology.