Preliminary Investigation of the Geometry and Kinematics of the Bangong-Nujiang Suture at the Basu Metamorphic Massif, SE Tibet

There are many uncertainties associated with the development and deformation of the Tibetan Plateau. The Basu Massif, located along the eastern Bangong-Nujiang Suture Zone, is an ideal locality to help provide constraints to resolve the geologic evolution of the Tibetan Plateau. The Basu Massif is characterized by high pressure-ultra high pressure (HP-UHP) metamorphic rocks, syn- and post-collisional granites, and a central Upper Paleozoic unit bounded by discontinuous belts of serpentinite. Field data suggests that the carbonates of the central Upper Paleozoic unit, serpentinites, granites and metasedimentary rocks are part of an isoclinally folded shear zone that may have been thrust from the Bangong-Nujiang Suture. New 40Ar/39Ar muscovite thermochronologic data from an augen gneiss, granite gneiss, and pegmatite are reported. The tight ages yielded (ca. 174 Ma) by the three samples are of significance and help resolve the timing of exhumation of the Basu Massif. Thermobarometric data from a retrogressed eclogite, amphibolite, granite, and mylonitic gneiss yield medium to high pressures and high temperatures. Exhumation of the metamorphic rocks would have likely been driven by slab breakoff due to the dominance of the Jurassic age granites in the area. There is no indication that, following the Cenozoic Indo-Asian collision, the Basu Massif behaved ductiley. Instead, our evidence suggests that the Basu Massif moved as a discrete crustal block