Cretaceous - Tertiary Geology of Central Tibet and Implications for Plateau Formation: A Synthesis

Here, we summarize recent geologic data pertaining to the geologic and uplift history of the central Tibetan Plateau since the Early Cretaceous. The Bangong suture between the Qiangtang (north) and Lhasa (south) terranes marks the closure of the Mesotethyan ocean and was the site of deep-marine sedimentation until ~125 Ma. The presence of ~118 Ma non-marine clastic rocks unconformably overlying these marine rocks show that the Bangong suture had closed and underwent sufficient deformation and uplift by this time to raise the region above sea level. Paleocurrent measurements indicate that drainage was to the south, off of the Qiangtang terrane and toward a developing epeiric seaway in the Lhasa terrane. By ~100 Ma this pattern was reversed, with strata deposited in the former seaway providing sediment to basins in the Bangong suture. This reversal was in response to the developing northern Lhasa terrane thrust belt. This thin-skinned thrust belt accommodated >50% shortening and was active between ~100 Ma and 50 Ma; it could have resulted in substantial elevation gain prior to the Indo-Asian collision. The central part of the Bangong suture underwent structural reactivation during the mid-Tertiary and achieved high elevation (~4.5 km) by 26 Ma based on oxygen isotope paleoaltimetry. The latter requires that any subsequent flow of mid-crust eastward from beneath central Tibet must have been balanced by a northward influx of Indian crust. Low-temperature thermochronologic studies show that most of central Tibet experienced <3 km of denudation since ~50 Ma, and intriguingly, show little signal of the Indo-Asian collision. Collectively, these results suggest that 1) central Tibet may have been characterized by significant elevation and low regional relief by 50 Ma, and 2) that plateau development may have initiated centrally and propagated outward.