藏南超基性岩的塑性流变

随着深部构造研究的不断深入,岩石流变作用日益受到人们重视,普遍认为塑性流变是地壳深部构造形成的主要机制。超基性岩的流变作用目前已成为研究上地幔流变、岩石圈板块动力学和热对流,甚至震源机制的重要内容。 本文拟通过对构成雅鲁藏布江蛇绿岩套底部的藏南超基性岩的研究,重点划分塑性流变的结构类型,探讨不同结构类型中橄榄石的组构特征及实际存在的滑动系,用不同方法计算超基性岩形成和侵位过程中的流动应力值,并认为由于橄榄石塑性流变而获得的晶格方位排列是造成地震波速度不连续性的主因,岩石的塑性流动有可能是深部能量释放和诱发

PLASTIC FLOW OF ULTRABASIC ROCK IN SOUTHERN TIBET

A study of plastic flow in some ultrabasic massifs located at the bottom of the Yarlung Zangbo ophiolite suite shows that these massifs have generally undergone plastic flow deformation. According to grain shape of mineral, main deformation phenomena, recrystallization degree and fabric charicteris-tics, the main plastic flow textures can be divided into the following three types: proto-texture-protogranular and protoplaty (mildly deformed facies), blastic texture-granular blastic and platy-blastic (moderately deformed facies), porphyroclastic mylonitic texture-porphyroclastic, mylonitic,and ultramylonitic (strong deformed facies). The first and the third are the main textural type of high temperatural plastic flpw, with the slip system being T (slip plane) = (001), t(slip direction) = 100] and T=(010), t = 100] respectively. The blastic texture is the main textural type of lower temperature plastic flow, with T=010], 100], and T=.001], 010].The flow stress value estimated based on dislocation density, subgrain and recrystallized grain size of olivine is 289× 105-5414 × 105Pa, increasing with intensifying strain.Compared with the slip system in olivine and flow stress value with the focal distribution of the Himalayan are vate seismic belt in the profile, it has been inferred that the bedded structure of the lithosphere formed by the crystal preferred orientation of olivine is one of the important reasons for discontinuous seismic wave velocity in the Himalayan area. Plastic flow in rocks is probably a major mode of releasing deep seismic energy and causing seismic activity.