鄂尔多斯盆地南缘晚古生代沉积物源及其对秦岭造山带北部演化的指示

摘要

The formation,evolution and sedimentary characteristics in the south margin of Ordos Basin are closely related to the activities of the Qinling Orogenic Belt in the south of North China Cratonic Basin.Provenance characteristics of late Paleozoic sediments in the area are studied so as to extract information on the evolution of the Qinling Orogenic Belt.Based on petrological characteristics from two field sections of Benxi-Shiqianfeng Formation in Chengcheng and Hancheng,provenance information of the late Paleozoic sediments in southern Ordos Basin and evolution process of the north Qinling Orogenic Belt in late Paleozoic is obtained through analysis of rock compositions,grain compositions,heavy mineral compositions and tectonic setting discrimination by Dickinson triangular diagrams.It reveals that the provenance of Benxi-Taiyuan Formation is originated from the southern margin of the Qinling Orogenic Belt of North China Plate,and the provenance of Shanxi-Shiqianfeng Formation is originated from the north Qinling tectonic belt.Initial point collision of Shangdan belt during late Devonian and late Carboniferous period resulted in the uplift of the southern margin of the North China Plate.From early Permian,Qinling Orogenic Belt entered into surface collision stage and resulted in uplift of the north Qinling back-arc basin and island arc belt successively,which became the main provenance of the south margin of Ordos Basin.The east-west collision like scissors between the Yangtze plate and the North China Plate resulted in the change of paleocurrent direction from northwest in the Shanxi Formation to northeast in the Lower Shihezi Formation.%鄂尔多斯盆地南缘位于华北克拉通盆地的西南部,其形成演化和沉积过程与华北克拉通南侧秦岭造山带的活动有紧密的联系.晚古生代沉积的物源特征能够帮助提取关于秦岭造山带的演化信息.基于对鄂尔多斯盆地南缘澄城和韩城2条出露本溪组－石千峰组的剖面岩石学特征的详细研究,从岩石性质、碎屑特征、重矿物组合和碎屑组分的Dickinson三角图解等方面进行分析讨论,获得了鄂尔多斯盆地南缘晚古生代物源的详细信息,并揭示了秦岭造山带北部晚古生代的演化过程.研究表明,本溪组－太原组的物源为秦岭造山带中的华北板块南缘带;山西组－石千峰组的物源来自于北秦岭构造带,物源区有向南迁移的特征.晚泥盆－晚石炭世商丹带的点接触初始碰撞造成华北板块南缘发生抬升,早二叠世秦岭造山带进入面接触碰撞阶段,造成北秦岭弧后盆地和岛弧带依次发生隆升,成为鄂尔多斯南缘沉积区的主要物源供给区.扬子板块与华北板块自东向西剪刀状的碰撞,造成鄂尔多斯南缘沉积的山西组－下石盒子组的古流向由南东－北西方向朝南西－北东方向的转变.