鄂尔多斯盆地奥陶纪“L”状边缘隆起演化过程及其构造背景

将鄂尔多斯盆地简化为近似直角梯形的等厚各向同性弹性薄板模型进行应力—应变场数值模拟,力图揭示鄂尔多斯地区奥陶纪发育的“L”状边缘隆起的形成背景及演化过程。模拟中Z轴方向应变(zε)正值区对应于盆地内部的隆起区,故zε正等值线形态对应于隆起形态。设定的多种不同的边界条件中,只有在南、西边界分别施以大小相同的边界应力时,εz正等值线形态才出现与实际地质情况相类似的“L”状,该边界条件下的模拟再现了盆地奥陶纪“L”状隆起的形成过程:在盆地南、西边界首先产生两个月牙状隆起,随着应力传递,南、西边界处的两个隆起扩展而连接,形成一个“L”状隆起,随后该隆起不断向盆地内部延伸。模拟结果证实由于奥陶纪鄂尔多斯盆地南缘秦岭海槽的向北俯冲及西缘贺兰海槽和秦祁海槽的东西向扩张,鄂尔多斯盆地南、西边界同时受到挤压作用,正是因为两边界所受挤压力大小相似,“L”状隆起才于盆地南西边界发育。

The Tectonical Background and Evolution Process of Ordovician Marginal L-Shaped Paleouplift in Ordos Basin

To find out the tectonic background and confirm the evolution process of the Ordovician marginal L-shaped(paleouplift) in Ordos Basin,a series of stress-strain simulations under various mechanic conditions were carried out,in which the basin was simplified into an isopachic,isotropic and elastic shell model.The positive strain along Z axis(ε_(z)) corresponded to the uplift,so the shape of positive ε_(z) isoline represented that of uplift.Only in the mechanic condition that the stresses imposed on the south and the west boundaries were equal did the ε_(z) isoline show the shape which was similar to the geological situation qualitatively.The simulation under this condition(recurred) the developing process of the L-shaped paleouplift.Two crescent uplifts appeared at the south and west edges of the basin followed by these two uplifts expanded and connected forming one larger L-shaped uplift,which extended toward the basin interior later.These numerical simulations proved that L-shaped(paleouplift) formed nearby the southwest edge of Ordos Basin because the intensity of the compression was similar which resulted from the subduction of the Qinling Trough in the south edge and the subduction of the Helan Trough and Qingqi Trough in the west edge respectively.