稳定的鄂尔多斯地块在整体运动吗?

Is the stable Ordos block migrating as an entire block?

以华北地区三维流变结构和活动地块划分为基础,结合速度结构、热结构等其他地质地球物理资料,建立起一个与实际情况较为相符的三维黏弹性体模型,在GPS速度场约束下,本文实现了华北及其邻近地区岩石圈动力学三维数值模拟.通过与GPS速度场及计算的欧拉极参数的拟合对比分析,详细论证了鄂尔多斯地块数值模拟结果的可靠性,并印证了鄂尔多斯地块横向上的水平运动具有良好的整体性.在此基础上,计算了鄂尔多斯地块沿深度变化的欧拉极参数,发现以下地壳为过渡带,中、上地壳与岩石圈地幔间的欧拉极参数存在明显的差异.对块体内部4个点速度随深度的变化的进一步分析表明,鄂尔多斯地块壳幔间水平运动差异主要表现为岩石圈地幔相对于中上地壳的逆时针扭转变形.因此,稳定的鄂尔多斯地块横向上的水平运动具有良好的整体性,但纵向上在下地壳处存在明显的水平运动差异,推测下地壳可能存在较强的剪切变形带.

Under the constraint of GPS velocity field, a 3D viscoelastic modeling was realized for studying the lithosphere dynamics of North China and its adjacent area based on the comprehensive geological and geophysical data, such as 3D rheological structure, the active blocks of China, velocity structure, thermal structure, et al. The reliability of modeling results was proved high by means of a detailed comparison of the fitting of GPS velocity field and the Euler Poles. It is confirmed that in the horizontal direction the Ordos block is moving as a whole. Based on the results, the Euler Poles of Ordos block along the depth were calculated, which presents an obvious difference between the upper-middle crust and the lithosphere mantle. A gradient zone of the horizontal velocity is located in the lower crust. We can get the anti- clockwise twist of the lithosphere mantle relative to upper-middle crust through furtherinvestigation of the velocity variation along the depth at 4 sites. So by this study, although the horizontal movement of Ordos block is moving as a whole in lateral direction, a gradient velocity zone exists in the lower crust. Those results imply a ductile shear belt in the lower crust of the Ordos block.