The Lhasa and Qiangtang terranes of Tibet collided following Late Jurassic–Early Cretaceous consumption of oceanic lithosphere along the intervening Bangong suture zone. This continental collision led to the development of the south-directed, northern Lhasa thrust belt that is exposed ~1200 km along strike in central Tibet. We conducted geologic mapping and stratigraphic and geothermochronologic studies in the Duba region of the northern Lhasa terrane, located ~250 km northwest of the city of Lhasa. In the Duba region, granites were emplaced into the mid-crust between 139 and 121 Ma and subsequently exhumed and juxtaposed against Cretaceous strata between 105 and 90 Ma in the footwall of an interpreted passive roof thrust system. We suggest that this structural style dominates the Cretaceous–early Cenozoic evolution of the northern Lhasa thrust belt and provides an explanation for the scarcity of basement rock exposures in the Lhasa terrane despite >50% upper crustal shortening. Furthermore, we highlight similarities between the collision-related northern Lhasa and Tethyan Himalayan thrust belts, both of which are bound by sutures and associated with underthrusting of lower plate lithosphere.

Abstract Anisotropy of magnetic susceptibility (AMS) combined with structural analysis are used in this work with the aim to characterize the tectonic evolution of the Triassic flysch within the eastern Tethyan Himalaya Thrust Belt in SE Tibet. The attitude of the magnetic foliation and lineation are concordant with the planar and linear structures of tectonic origin defined by the preferred orientation of the iron-bearing silicates. Two different tectonic domains can be defined: (a) the southern domain is controlled by the Eohimalayan tectonic foliation (S1) recorded in the magnetic foliation which trends east–west and dips to the north; (b) the northern domain is dominated by the Neohimalayan magnetic foliation with WNW–ESE strike and dips to the south opposite to the vergence of the main structures. A slightly prolate magnetic ellipsoid has been found in between the two domains recording the intersection of S1 and the subtle development of the S2 tectonic foliation. Hinterland propagation of the deformation lead to the Great Counter backthrust generation, pointed out by the SSW steeply plunging magnetic lineation. Furthermore different orientations of magnetic foliation may indicate an Early Miocene c. 20° clockwise vertical-axis rotation.

Abstract The Selin Co basin in the northern Lhasa terrane includes more than 3000 m of upward coarsening Lower Cretaceous strata, and the sedimentary sequence from the flysch to the molasse indicates the evolution of a foreland basin. Petrographic analysis shows that sandstones are rich in volcanic and sedimentary lithics and most of them fall into recycled orogen and magmatic arc. Uranium–lead (U–Pb) ages were determined for 435 detrital zircons from the Lower Cretaceous strata in the Selin Co basin. Relative probability of detrital zircon ages shows the Eshaerbu Formation was rich in zircon grains with the age of 125–140 and 160–180 Ma, and the Duoni Formation was dominated by one main age cluster of 125–150 Ma. Analysis of the potential provenances suggests the Early Cretaceous zircon grains were primarily derived from the Gangdese magmatic arc to the south. The youngest zircon ages in the lowermost exposure of the Eshaerbru Formation are c . 130 Ma, providing a maximum depositional age of sediments in the Selin Co basin. Collectively, our studies, together with previously documented Cretaceous thrusting in the Lhasa terrane, suggest the Lower Cretaceous Selin Co basin was deposited in a retroarc foreland basin. From 145–90 Ma, a retroarc foreland basin was presumed to develop in the Lhasa terrane, migrating from the south to the north. Crustal thickening, likely associated with the evolution of the retroarc foreland basin, was speculated to start in the Early Cretaceous in the Lhasa terrane.