It is unclear what caused the Bangong Nujiang suture
zone in the
central Tibetan plateau to rise from less than 2 km in early Cenozoic
to more than 4 km at present. The zircon U–Pb ages and trace
elements of samples from the Niubao Formation in the Paleogene of
the Nima basin were analyzed and tested. Combined with the isostasy
theory, the surface uplift height of the Nima Basin during the Cenozoic
period was calculated. The zircon U–Pb age results of the Niubao
formation are consistent with the ages of the Lhasa terrane on the
south side of the basin, the Qiangtang terrane on the north side,
and the uplift in central. The zircon Eu/Eu* results show that the
crust in central part of Tibetan plateau thickened by ∼20 km
in Paleogene, resulting in ∼3 km surface uplift. Sediments
created a total of about 1 km of surface uplift throughout the Paleogene,
and the deposition rate began to slow down significantly at ∼40
Ma. Therefore, it is inferred that in the early Cenozoic, the uplift
of the valley was mainly caused by sedimentation. With the continuous
downward subduction of the Indian plate, at about 40 Ma, factors such
as crustal shortening dominated the uplift of the central valley,
and the uplift caused by deposition only accounted for a very small
part. In general, the uplift of the Central Valley in the Paleogene
was mainly affected by crustal shortening, but a quarter of the surface
uplift was caused by the accumulation of sediments.