West Tianshan High-pressure Veins And Host Rocks Typical Mineral Electron Microprobe Analysis And Fluid Tracer Significance

Western Tianshan belt, which locates between the plate of Yili-Central Tianshan and plate of Tarim basin, is a part of the famous Central Asian Orogenic Belt. It can be originaed to late Paleozoic orogenic. Our study area is located in southen part of the West Tianshan, which is a high-pressure metamorphic belt representing by the development of eclogite and blueschist. This high-pressure metamorphic belt is characterized by the assemblages of high-pressure metamorphic minerals, comparing with other veins, it composed garnet, omphacite, phengite, zoisite and so on. High pressure veins in Orogenic belt are the direct records of the activities of deep fluids in ancient subduction zone, which can provide direct object in discussing deep fluid in the ancient subduction zone. However, there are still two kinds of recognization on the mechanism of the formation of high-pressure veins. One of the views is that the vein is the product of progressive metamorphism.The other view suggests that the vein is the result of retrograde, which turned out the retrograde mineral phase at the edge of single minerals. The differences between end-high-pressure metamorphic minerals are often good instructions to pressure and temperature, such as garnet, omphacite and phengite and so on. Non-destructive electron probe microanalysis is a good method to study the composition of high-pressure metamorphic minerals provide a very convenient methods to trace the formation of the veins, In this paper, inorder to explore characteristics of activity of deep fluids in ancient subduction zone in Western Tianshan, we take electron microprobe analysis as a main method in analyzing the Western Tianshan high-pressure veins and their host rocks.This article focuses on electron microprobe analysis of the typical high-pressure metamorphic minerals, such as garnet and omphacite. The results show that the composition of garnets did not changed by the formation of the vein. The results of electorn probe on profiles of single garnets show that the composition did not chang from the edge to the center in any of these single garnets, which indicating that the high-pressure vein is the product of metamorphism. The omphacite compositions in the vein are similar to those away from vein by different distances in host-rocks, which also indecates that the high pressure vein is the product of progressive metamorphism.