平南幔源包体中橄榄石的显微构造研究及其意义

平南玄武岩中的尖晶石二辉橄榄岩包体的平衡温度为930~980℃, 平衡深度为59~74km, 包体中橄榄石的扭折带滑移系多为(010) 100], 但也有(001) 100]的滑移系类型; 斜方辉石的滑移系为(100) 001], 它们均为高温低应变速率下的滑移系, 说明该区的上地幔主要是在高温低应变速率条件下经历了塑性变形作用.橄榄石位错组态多样, 有自由位错、位错壁、位错弓弯、缠结、{110}滑移带, 反映了上地幔的塑性变形特征.根据位错壁的大小估算, 上地幔差异流动应力为24.5~42.1MPa, 流动速率为2.93×10-17~8.36×10-16s-1, 有效粘度为1.72×1023~2.80×1024 Pa·s, 特征与中国东部新生代上地幔较为一致, 反映同处于拉张环境. 

OLIVINE MICROSTRUCTURES FROM MANTLE-DERIVED XENOLITH IN PINGNAN COUNTY, GUANGXI

The equilibrium temperature of the mantle-derived spinel lherzolite xenolith in the basalt in Pingnan County, Guangxi lies between 930 and 980 ℃, and its corresponding equilibrium depth between 59 and 74 km. The kink-band sliding system of the olivine in the mantle-derived xenolith is often (010) 100], but sometimes (001) 100]. However, the kink-band sliding system of orthopyroxene is (100) 001]. All these sliding systems occurred both at the high temperature and at the low strain rate, indicating that the upper mantle of the region experienced the plastic deformation both at the high temperature and at the low strain rate. Varieties of dislocations are present in the olivine, such as free dislocation, dislocation wall, dislocation bow, tangle, and (110) sliding system, indicating the plastic deformation features of the upper mantle. The size of the dislocation is used to estimate the following features of the upper mantle: the differential flow stress 24.5-42.1 MPa, the flow rate 2.93×10-17 -8.36×10-16s-1, the effective viscosity η 1.72×1023-2.80×1024 Pa·s. All these upper-mantle features are in agreement with those in the Cenozoic eastern China, showing that they both occurred in the same tensile environment.