Palaeogene growth of the northeastern Tibetan Plateau: Detrital fission track and sedimentary analysis of the Lanzhou basin, NW China

The Palaeogene evolution of the northeastern Tibetan Plateau remains elusive, because of the paucity of well-dated long-lasting and continuous sedimentary records. In this work, we present a detailed detrital apatite fission track thermochronology and stratigraphic study in the Lanzhou basin, located on the eastern-most margin of northeastern Tibet, where Eocene to middle Miocene sediments are well preserved. Combining the analysis of sedimentology records and synsedimentary tectonic structures, four regional tectonic phases are deciphered (52-47 Ma, 40-32 Ma, 23-20 Ma and < 16 Ma, respectively). These episodes were spaced out by three periods of tectonic stability or quiescence linked to regional relief-reduction. Our apatite fission-track data suggest that far-field stress due to the India-Asia collision had been propagated to this region since early Eocene, and the modern northeastern portion of the Tibetan Plateau has been buildup since then. Thereafter, the growth of the northeastern Tibetan Plateau was dominated by a tectonic activity/inactivity cycle until late Miocene. Thus, the regional growth history appears to have been episodic in nature during the Cenozoic.