鄂尔多斯盆地西部边界的确定及其地球动力学背景

Determination of the Borderline of the Western Ordos Basin and Its Geodynamics Background

鄂尔多斯盆地西部边界特别是不同时期原型盆地具体边界的确定,是目前该盆地西缘亟待解决的重大科学和生产实践问题之一。作者们着重从盆地西缘地区基本地质事实出发,充分汲取前人的有益成果,历史的分析西缘构造演化及地球动力学特点,紧密结合不同时期西缘盆-山转换的沉积响应,合理利用地震资料及其他第一手资料,认为鄂尔多斯盆地属华北板块的一部分,其形成和发展具体受四周的古祁连洋、古秦岭洋、不同时期的特提斯洋、占亚洲洋(古西拉木伦洋)及古太平洋(伊佐奈岐板块)控制。在此构造背景条件下,盆地西界不同时期范围和形态是不同的。早古生代盆地西缘为主动陆缘性质的弧后盆地;晚古生代盆地西部属被动陆缘构造背景上的滨浅海盆地;文中明确提出,晚三叠世鄂尔多斯原型盆地西界向西越过六盆山,连接六盆山盆地,直逼河西走廊靖远、景泰莫亦山附近,甚至在祁连山区也能找到其踪迹;不仅如此,笔者还认为“银川古隆起”及“西缘古脊梁”在印支期是不存在的,更不存在一个统一的南北走向的前陆盆地与沉降中心;燕山主期(J3)盆地西缘可能隆起,使得六盘山盆地和鄂尔多斯盆地具一定的分割性,但随后在早白垩世又被夷平,鄂尔多斯盆地又与包括六盘山盆地在内的西部白垩纪盆地连通,鄂尔多斯盆地现今西界最后形成的时间应在喜马拉雅晚期(8Ma以来),这也是盆地西缘桌子山-贺兰山-六盘山最后定型的大致时间,它们是印度板块和太平洋板块远距离应力作用的结果。

It is one of important question in science theory and production practice in Western Ordos basin to determinate the western borderline of the basin, especially, to determinate the proto-basin borderline in different geologic time now. Based on the basic geologic proof, the achievements that were acquired by former geologists, through analyzing geotectonic evolvement and geodynamics characteristics and linking with analysis of sedimentation, with the latest seismic and other data, thought that Ordos basin belongs to a part of Northchina palaeoplate and both the formed and developing of Ordos basin were controlled by palaeo-Qilian Ocean,palaeo-Qinling ocean, palaeo-north Asia Ocean（Xilamulun Ocean ） palaeo-Pacific Ocean and Tethys in different time. In above-mentioned geotectonic setting, the western borderline and shape of the basin were different, In early Paleozoic, the western borderline belt of the basin were back-arc basin located in Active triphibian margin. In late Paleozoic, the western borderline belt of the basin were coastal basin located in passive triphibian margin. This paper put forward that, in late Triassic, the western borderline of proto-basin of Ordos basin gots across Liupanshan mountains , linked with Liupanshan basin, and extended to Hexizoulang Corridor, ＂ Yinchuan ancient rise ＂and ＂Western ancient triphibian girder ＂were not found and the both the foreland basin and subside center which ever though were south-north in strike not found, either. The western borderline of the basin may rise in Main Yanshanian period（J3） and made Liupanshan basin separated from Ordos basin. In early Cretaceous, Liupanshan mountains were leveled to the ground and Ordos basin connect with western Cretaceous basin including Liupanshan basin late. The western borderline of the Ordos basin which can saw now were formed in late Himalayan period （following 8 Ma）. Zuozishan mountains-Helanshan mountains- Liupenshan mountains were formed in late Himalayan period （following 8 Ma）, too. These geological phenomenon were the resuh of the stress effect of far distance, which were caused by active of both India and Pacific Ocean plate.