HIGH PRESSURE ECLOGITE METAMORPHIC ZONES AND PROTEROZOIC COLLISION IN THE QINLING OROGEN

Recently two high-pressure metamorphic zones have been found in the Qinling Group inthe North Qinling orogen. They are exposed along the inner sides of the northern and southernboundaries of the Qinling Group respectively. The northern zone consists mainly of eclogiteswith garnet amphibolite, garnet-bearing amphibolites, garnet-and phengite-bearing felsicschists. The southern zone is composed of garnet clinopyroxenite and garnet amphibolite.Metamorphism involved three stages : the eclogite or garnet clinopyroxenite stage, garnet am-phibolite stage and amphibolitite stage. The first two stages are related to the intense crustalthickening caused by the collision between the North China plate and South China plate in theProterozoic. The last stage resulted from the decompression following the crustal uplift in thelate stage. In the early and middle（eclogite） stages of the plate collision the pressure was 1-1. 2 GPa and the temperature was in the range of 600-700℃. In the late （amphibolite） stage,the pressure dropped to 0.4-0. 5 tJPa and the temperature was 550-600℃.