二维重力正演在六盘山盆地西南缘构造样式分析中的应用

六盘山盆地南部处于旋扭构造的收敛端,地表和地下构造极其复杂,构造样式认识不清成为制约勘探的关键问题。盆地西南缘构造样式问题的焦点在于沙沟断阶带是否存在大规模的逆冲推覆体。针对这一问题,采用二维地震剖面重力正演的方法来分析构造样式。首先确定这一地区的密度分层方案;其次,根据两种可能的构造样式以X测线为基础分别建立地质模型,然后进行重力正演模拟;最后将得到的结果与实测数据进行比较。结果表明,与逆冲推覆样式相比,走滑斜冲样式的模拟结果与实测重力剖面更吻合。同时,综合最近的野外构造调查成果和最新地震剖面解释方案,认为六盘山盆地西南缘不存在大规模的逆冲推覆体,主要发育走滑构造。

The application of 2-D gravity forward modeling in analyzing the structural pattern of the southwestern margin in Liupanshan Basin

The north Liupanshan Basin is localized in the convergence tip of rotation-shearing tectonics, resulting in the complex of both surface and underground structures. The key problem of petroleum exploration lies in structure style, which focuses on whether gigantic thrust nappes in the southwestern margin exist or not.According to this problem, this paper analyses structural pattern mainly using 2-D gravity forward. First of all, the regional layer-divided scheme of formation density is determined. Second, based on the two possible structural patterns of seismic line X, geological model is set up which is then used for gravity forward modeling. Finally, we compare the result with measured data. Compared with thrust nappe structure, the modeling result of strike-slip and oblique thrust style is more consistent with measured gravity profile. Synthesizing the latest research result of field structures and the interpretation of the newest seismic profile, it can be concluded that the southwestern margin in Liupanshan Basin is not characterized by gigantic thrust nappes, but compresso-shear structures.