华北克拉通上地幔变形及其动力学意义

华北克拉通从稳定到破坏的演化过程对有关地球动力学的经典理论提出了挑战，研究其独特的演化历史是固体地球科学研究的一项重要内容。上地幔矿物晶体的各向异性记录了上地幔发生构造变形的信息，研究上地幔地震波各向异性能够揭示现今和构造历史时期所发生的构造运动。本文总结了近年来作者在华北克拉通地区所进行的高密度、覆盖广泛的地震波横波分裂观测研究结果。横波分裂的快轴方向与绝对板块运动方向的不一致，以及横波分裂参数快速的空间变化特征表明了华北克拉通的SKS横波分裂主要反映上地幔的变形。观测结果表明：鄂尔多斯块体保留了克拉通较弱的各向异性特征，其西端体现了元古代克拉通拼合的变形特征； 中新生代华北克拉通破坏事件以不同的机制主导了华北克拉通中部和东部的上地幔变形，在东部地区北西-南东向的拉张应力作用使得快轴方向平行于拉张方向，而在中部则因受到较厚岩石圈的阻挡使得地幔流动改变了方向，因此造成了北东和北北东向的岩石圈拉张。

Upper mantle deformation beneath the North China Craton and its implications for craton evolution

The unusual reactivation of the North China Craton(NCC)challenges the classical theories concerning the strength and stability of cratonic lithosphere and plays important roles for improving our understanding of the plate tectonics. The origin of seismic anisotropy is of fundamental importance to the understanding of the lattice?preferred orientation(LPO)of mantle minerals and mantle flow that produces it. The LPO of anisotropic olivine crystals in the upper mantle is believed to be the primary cause for SKS wave splitting，and the measurement of seismic anisotropy can provide key clues to distinguish deformation pattern of the upper mantle. In this paper, 493 shear wave splitting results in the North China Craton by using SKS phase，which are from 138 stations covering the NCC with dense spacing，are summarized. The strong anisotropy，rapid variation of splitting parameters imply that the shear wave splitting is mainly caused by the upper mantle anisotropy and reflects the effects of tectonic controls. We suggest that the Ordos block possibly remains the weak anisotropy of the Precambrian craton similar to that of the Kaapvaal Craton，south Africa，Proterozoic amalgamation generated the seismic anisotropy in the boundary zone between the Ordos Block and the Trans?North China Orogen，while the anisotropy in the eastern Trans?North China Orogen and eastern NCC were possibly associated with the lithospheric rejuvenation during the Late Mesozoic to Cenozoic.