THE MESO-CENOZOIC ACIDIC-INTERMEDIATE MAGMATISM AND TECTONIC EVOLUTION OF GANDISE MASSIF, TIBET

The Meso-Cenozoic acidic-intermediate magmatism in the Gandise massif would be divided into three belts. The magmatic rocks in the north belt were formed in Yanshanian epoch as Ⅰ-type in early, transitional type in middle and S-type in late stages, respectively under the tectonic background of plate subduction, suture and collision, reflecting the evolution of Bangonghu-Nujiang Tethys in the north. The middle and south magmatic rock belts express the whole evolving course of the Yarlung Zangbo Tethys in the south. The rock bodies in the south belt were formed mainly in Yanshanian, followed by Himalayan epoch. Their origin was closely related to the northward subduction of Tethys oceanic crust in late Yanshanian epoch. The Himalayan magmatism of syn-collision after subduction is evidently recorded in this rock belt. The middle belt contains mainly early Himalayan rock bodies, with minor Yanshanian ones, of which most were the products of syn-collision magmatism. So the magmatites in this rock belt were formed under the condition of syn-collision during the late stage of subduction and after the suturing. Patches of porphyries of late Himalayan epoch broadly occur in the whole Gandise massif, showing the intracontinental extension after the collision and orogeny in the region.