Abstract:

A new eclogite belt, more than 100 km long and 2—3 km wide, was discovered in Sumdo in Lhasa terrain of Tibet. The studies show that the metamorphism of Sumdo eclogites has undergone three stages,i.e., the prograde episodeeclogite facies, peak eclogite facies and retrograde amphibolite facies. According to geothermobarometry of garnetomphacitephengiterutile, the pT estimations of peak metamorphic stage are 760—800 ℃，33—39 GPa, which implies that the Sumdo eclogites may have undergone UHP metamorphism. The pT paths are characterized by the clockwise hairpinlike shape, which indicates that the Sumdo eclogites have undergone fast subduction and exhumation. The discovery of Sumdo eclogites suggests that there may be a new suture zone in the Lhasa terrain, which would be very important for understanding the tectonic evolution of the Lhasa terrain and the PaleoTethys.

Key words: UHP eclogite, metamorphic evolution, Sumdo, Tibet