Study On Basalt Metamorphism And Deformation Characteristics In GangtangCuo Area Of Tibet Qiangtang

Study area is located in the hinterland of Qiangtang Basin in Tibetan Plateau and the structural position is in the juncture area of the Gondwana and Eurasia continent. Study area belongs to typical subduction- accretionary complex. Therefore, the study area is a key area to solve the Tethys evolution and the formation of early Tibetan Plateau.I investigated the structural deformation stage of the basal in the study area by in-depth analysis to the features of basalt metamorphism and deformation characteristics. So, on the basis we can further study suture zone metamorphic rocks (blueschist, eclogite, etc.), establish the model of suture zone formation and evolution, ascertain the relationship between the east-west structure and south-north structure, and provide some evidences for setting up structure framework of the study area.Basalt in the study area is divided into two generations: one is the middle Carboniferous-Early Permian basalt, which appears in small amounts in the Xueshuihe, Lanling and Bingshuihe formation complexes as some interlayer; the other is the middle Permian basalts which mainly appear in Jiaomuri area, are related to ophiolites and well preserved. Basalt metamorphism and deformation in the study area is uneven. Lots of pores and almonds, obviously flattened and lengthened, can be seen in basalts with metamorphism and deformation. By doing some stress analysis, strain measure and some relevant charts, we can get more information about tectonic stress situation of the study area.We find the mineral assemblage in basalt of study area, which includes albite, chlorite, actinolite and Epidote etc., and this assemblage belongs to typical green schist facies.Because of much glaucophane, it can be further affirmed to belong to high-pressure regional metamorphic facies series. It also accords with low-temperature and high-pressure features of the regional subduction environment.The first phase of basalt deformation in the study area is nearly north-south shear deformation which formed a number of melange rock blocks or slices, some with distinct shear sense indicators; the second phase of basalt deformation in the study area is that nearly east-west compression formed a series of buckling folds, some of which are often big basalt anticlines. In the second deformation phase, some non-root hook folds, vein folds and permutated foliations are commonly seen.