THE AGE OF FORMATON OF THE HOULONGMENSHAN INTERMEDIATE-PRESSURE METAMORPHIC TERRANE IN SICHUAN

The metamorphic terrane in qustion occurs in a Paleozoic to Triassic geosynclinal formation.The metamorphism belongs to regional dynamothermal metamorphism of intermediate-pressure facies series.It was formed in the late Indosinian period,accompanied by strong folding,migmatization and granitization. It originated from collision of the Bayan Har block and the Yangtze block. The ascent of the thermal flow might be related to intracontinental subduction and intracrustal partial melting.This intermediate-pressure metamorphic belt is associated with low-pressure transitional regional dynamothermal metamorphic belt and regional dynamic metamorphic belt in Triassic flysch to its west.