大别山碧溪岭及南山岭两岩体中橄榄石的显微构造特征

大别山南山岭和碧溪岭石榴橄榄岩中的橄榄石具有不同的显微构造特征，前者基本不发育位错，而后者的位错比较普遍。碧溪岭橄榄石的微观晶形可分为球形颗粒和多面块体两类。球形颗粒内位错密度极低，是局部重结晶作用的结果，表明样品曾受到瞬间高温的作用；而多面块体内则分布着较高密度（～2×10^8／cm^2）的位错，其中有些微区的位错已显著扩展，形成层错，而另外一些区域中位错依然保持全位错的构形，表明各微区的层错能可能不同。层错能的差异最可能源于各微区成分的不同，实验结果显示Mg含量较高的微区，易形成层错。多面块体内的位错有明显运动迹象，表明样品曾受到长期、和缓的温度与差应力的联合作用。据此推测，碧溪岭地区板块间曾发生长期的相互挤压作用和不均匀的塑性变形，并最终发生瞬时激烈碰撞，由此产生的热量导致一些变形严重的微区发生重结晶形成球形颗粒，而未发生重结晶区域的位错则基本保持碰撞之前的组态。本文为碧溪岭地区板块俯冲和折返的超高压变质过程和演化历史及南山岭岩体形成于碰撞造山后的认识提供了流变学的证据。

Microstructure characteristics of olivines from Nanshanling peridotite and Bixiling peridotite, Dabieshan

The olivine in Nanshanling peridotite of Dabieshan exhibits obviously different microstructure characteristics from that in Bixiling peridotite of Dabieshan. Dislocations are rarely detected in the former, while they distribute widely in the latter. The microcosmic shapes of the olivine in Bixiling can be distinguished as two classes, i.e. global particles and polyhedral pieces. Dislocation density in the global particles is very low, which should results from local recrystallization, indicates that the specimens had suffered instantaneous high temperature. High density dislocations（ - 2× 10^8/cm^2 ） occur in the polyhedral pieces. Dislocations have extended and stacking faults have formed in some zones while dislocations have not extended in others zones. The phenomenon implies that stocking fault energy of different zones might be different. The distinction of stocking fault energy generally originates from different composition in different zones. The experimental result shows that stocking faults occur in the zones with higher Mg content. Dislocations in the polyhedral pieces present marked motion characters, which indicates that the specimens had been subjected to meek action of heat and differential stress in long term. It can be derived from these results that plates in Bixiling had jammed for long period, which led to nonhomogeneous plastic deformations. Finally, momentary violent collision occurred. The heat produced in the collision resulted in local recrystallization of largely deformed zones and formation of global particles, while dislocations in the unrecrystallized zones kept ultimately their configuration as that before collision. The present investigation provides theology evidences for the postulate that Bixiling came from deep-subduction and rapid exhumation of plates, while Nashanling formed after the collision process.