Abstract:

The structural deformation and muscovite and amphibole 40Ar39Ar dating of muscovite quartz schist, eclogite and retrograde eclogite indicate that an Indosinian orogenesis occurred in 220240 Ma in the Lhasa Terrane, which caused the closure of PaleoTethys ocean basin and the collision between the northern Lhasa Terrane and southern Gondwana. The accordance of muscovite and amphibole 40Ar39Ar dating among eclogite, retrograde eclogite and muscovite quartz schist shows that the eclogite exhumation and Indosinian collisional orogenesis occurred simultaneously, which suggests that the regional ductile extrusion should be the main mechanism for the exhumation of Sumdo eclogite. The existence of large scale granite belt of late Indochina EPoch in the Lhasa Terrane, with the high precision single zircon UPb ages of 210190 Ma, confirms the syncollisional exhumation of eclogite from the another side, indicating that the eclogite exhumation had no relation to the postorogenic extension and granite activities.

Key words:  Lhasa Terrane, eclogite, syncollisional exhumation, structural deformation, 40Ar39Ar chronology