DISCOVERY OF CROSSITE AND PHENGITE ON THE NORTHERN MARGIN OF THE CENTRAL TIANSHAN MOUNTAINS AND ITS GEOLOGICAL SIGNIFICANCE

There exists an Early Paleozoic tectonic mélange zone on the northern margin of the Central Tianshan Mountains.The authors first found glaucophanic amphiboles and phengite in mélanges at Wusitegou and Gangou in the eastern sector of the zone.Electron microprobe analysis shows that the glaucophanic amphiboles are represented by crossite formed at a pressure of 6.7×10 5 kPa.The b0 value of the phengite is 9.041 and the ion number Si in its crystal structure averages 3.43.The discovery of theses high pressure minerals provides reliable evidence for the metamorphic facies of the tectonic mélange zone on the northern margin of the Central Tianshan Mountains,thus furnishing necessary information for the tectonic evolution and paleo plate motion of the Tianshan orogenic belt.