Tracing the Transhimalayan magmatic belt and the Lhasa block southward using zircon U-Pb, Lu-Hf isotopic and geochemical data: Cretaceous - Cenozoic granitoids in the Tengchong block, Yunnan, China

Lu-Hf-isotopic data of late Cretaceous - Paleocene granites are indistinguishable from those of granites of the Central Lhasa block. Thus, we tentatively correlate the late Cretaceous granites of the Tengchong block with those of the Central Lhasa block. The boundary between the South and Central Lhasa blocks in western Tengchong may be exposed in the NNE-striking, dextral Nabang shear zone along the Chinese-Myanmar border region, which hosts early Eocene granitoids with εHf(t) values >0. The Lu-Hf-data of the zircons from the gneissic Miocene granodiorite indicate a juvenile crustal substrate in the western Tengchong block as well. The synkinematic Miocene granodiorite provides an important age constraint for dextral shear at mid-crustal levels, which was active until at least c. 19-20 Ma in the Nabang shear zone. This Miocene intrusion may be a first indication that active margin tectonics lasted 20-25 Ma longer than in the Gangdese belt and possibly was associated with deformation partitioning in the hinterland produced by increasing obliquity of subduction during clockwise rotation of Sundaland during the India-Asia collision.