Abstract: This paper has studied the deformation features of the mylonitic mantle xenolith,including deformation-induced microstructures,dislocation substructures and fabric. It is confirmed that mylonitic mantle xenolith is representative of upper mantle shear zone. The physical conditions ofthe formation of upper mantle shear zone have been determined as T=729～828 ℃,P=1.10～1.38GPa,σ₁-σ₃=97～150MPa,ε=10^-14～10^-12s^-1,η=10～1000EPa·s,Z=37～45km.Based on these results,it is suggested that the shear zone is a small-scale gently dipping shearzone,which is related to the mantle diapir and is a zone of strain concentration, which causes theseismic anisotropy of upper mantle and is presumably related to the seismicity of the region.

Key words: Microstructure, Shear zone, Upper mantle, Mylonite, Mantle xenoliths, Yitong graben

摘要： 通过研究糜棱岩型幔源包体的变形显微构造、位错亚构造及组构特征,确定它是上地幔剪切带的代表物质。该带形成温度为729～828℃、压力为1.10～1.38GPa、差异应力为97～150MPa、应变速率为10¹⁴～10^-12s^-1、等效粘滞度为10～1000EPa·s和深度为37～45km.这是一种与地幔底辟作用有关的规模较小的缓倾斜剪切带,也是应变集中带,能导致上地幔地震波速各向异性,并与地震活动有关。

关键词: 显微构造, 剪切带, 上地幔, 糜棱岩, 幔源包体, 伊通地堑