New progress in the study of the Nyalam Group in the Gyirong area, southern Tibet

Abstract: The results of mapping by the structure-strata (rock)-event method indicate that the original Nyalam Group in the Gyirong area, southern Tibet, actually includes metamorphic strata and metamorphic plutonic rocks and should be integrated. The integrated metamorphic plutonic rocks are called the Sima gneiss, which was emplaced in the Jinningian Stage; whereas the metamorphic strata are called the Nyalam Group-complex, including the Quxam and Jiangdong Formation-complexes. They are in ductile fault contact with each other and were deposited in the Paleoproterozoic. Both underwent medium-pressure kyanite-staurolite subfacies regional dynamothermal metamorphism in the terminal Luliangian Stage and were subjected to amphibolite facies metamorphism in the terminal Jinningian Stage and greenstone facies retrograde metamorphism in the Himalayan Stage together with the Sima gneiss.