| 摘 要： | In view of their distinct NWW trending and their decreasing geological age from north to south, intermediate-acid magmatic rocks in the southern part of Xizang can be divided into three petrographical belts in general: (1) the Kangdese belt (120--10 m.y.). The major part of the belt is mainly composed of diorite, granodiorite, etc.,more intermediate in chemical composition and ranges from 120---70 m. y. in age; (2)the Lhangoi Kangri belt (30 m. y.) ; and (8) the Himalaya belt (20--10 m. y.). From their intruding features, spatial-temporal consistency, intruding scale, petrological characters and chemical Composition, it is suggested that these three petrographical belts secm to be closely related to plate underthrust and collision. It may be concluded that the major part of the Kangdese belt is resulted from the underthrust of the Indian Ocean Plate towards the Eurasian Continental Plate while the Lhagoi Kangri belt and the Himalaya belt are the results:of collision of the Indian sub-Continental Plate overlying the .Indian Plate with the Eurasian Continental Plate.
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