西昆仑山库地变质橄榄岩的显微构造特征

MICROSTRUCTURAL FEATURES OF META. MORPHOSED PERIDOTITES IN KUDI,WESTERN KUNLUN, CHINA

西昆仑山库地变质橄榄岩块是肢解了的震旦纪一早古生代蛇绿岩碎片。变质橄榄岩以残斑结构为主，呈现粗粗结构向残班结构的过渡和残斑结构向板状等粒结构的过渡。此岩石有明显的变形结构，橄榄石变形时的滑移系为｛０ｋｌ｝［１００］。橄揽石发育有代表高温（８００℃以上）的位错构造，也有代表低温的位错构造。表明此变质橄榄岩经受了上地幔环境下发生的高温塑性流变和侵位过程中及侵位后所经受的低温高应变速率条件下的变形。上地幔环境下变形时的差异应力约为８０ＭＰａ，应变速率约为１．９６×１０－１２ｓ－１－７．０３×１０－１０ｓ－１。此变质橄榄岩代表由大陆裂谷发展起来的洋盆下的地幔，产出的构造环境为洋脊－裂谷带。

The metamorphosed peridotite blocks in Kudi area, Western Kunlun Mt., China arethe fragments of dismembered Sinian-Early Paleozoic ophiolites. The metamorphosedperidotites are characterized by porphyroclastic texture, which shows the transitioneither from protogranular to porphyroclastic textures, or from porphyroclastic totabular equigranular textures. The rocks show strong lattice preferred orientation ofolivines, the active slip system of which during the deformation was {0kl} [100].Olivines in the rocks possess both dislocation substructures representative of hightemperature and low temperature plastic deformations. It indicates that the metamorphosed peridotites have subjected to either high temperature flow in upper mantlecondition, or low temperature, high strain rate deformation during or after emplacemellt. The differential stress during the deformation under upper mantle conditionwas about 80 MPa, while the strain rate was about 1.96×10-12s-1-7.03×10-10s-1.These metamorphosed peridotites are representative of upper mantle beneath oceanicbasin, which evolved from continental rift. The tectonic environment at that timewas representative of oceanic ridge-rift zone.