Discovery of ≥ 105 Ma continental redbeds in the Qiangtang Block: Implications for the early uplift of central Tibet

The Abushan Formation represents the oldest continental redbed deposit overlying Triassic-Jurassic marine strata in the Qiangtang Block. Knowledge of the exact depositional age of the Abushan Formation is important to reconstruct early history of surface uplift in central Tibet. Pollen and magneto-stratigraphy studies from central Qiangtang suggest that the Abushan Formation was deposited during the mid-Cretaceous; however, confirmation through isotopic geochronological data is still required. Here we describe the newly studied Madeng section exposing fluvial Abushan Formation redbeds at the base and felsic volcanic rocks at the top. SIMS U-Pb dating of zircons from one sample of these volcanic rocks yield a weighted mean ²⁰⁶Pb/²³⁸U age of 105.1 ± 0.9 Ma, indicating latest Early Cretaceous (late Albian) deposition of the Abushan Formation. Our data support the Abushan Formation redbeds were deposited in intermontane basins in an intra-plate tectonic setting following the collision, suturing, and amalgamation of the Qiangtang and Lhasa blocks.