Origin and metamorphic evolution of the Nyingchi Complex, eastern Lhasa terrane, southern Tibet: Constraint from the zircon U-Pb geochronology

A petrological and geochronological study was produced on the Nyingchi Complex rock from the southeastern part of the Lhasa terrane, Tibet. The results show that the meta-sedimentary rocks of the Nyingchi Complex consist mainly of gneiss and schist, and metamorphosed under the medium-pressure amphibolite-facies. The zircons from these rocks contain an inherited detrital core and an overgrowth metamorphic rim. The detrital zircon core yielded variable ages ranging from Neo-Archean to Late Paleozoic, with main populations at ca. 1560Ma, ca. 1190 Ma, ca. 620 Ma and ca. 340Ma, respectively. The zircon rims of two samples yielded metamorphic ages of 53Ma and 27Ma, respectively. These indicate that the sedimentary rocks of the Nyingchi Complex deposited during Paleozoic time, and their material provenance recorded mainly the tectono-thermal events related to the Grenville and Pan-Africa orogenies, and that the Lhasa terrane derived from the north margin of the Gondwana continent. The Nyingchi Complex, representing the hinging wall of the subduction zone, experienced the Eocene and Oligocene metamorphism during the collision/subduction between the India and Eurasia continents.