Carbonate stable and clumped isotopic evidence for late Eocene moderate to high elevation of the east-central Tibetan Plateau and its geodynamic implications

Abstract : The topographic history of mountain belts reflects changes in lithospheric structure and rheology and exerts an influence on climate. Although substantial progress has been made to constrain the growth history of the southern Tibetan Plateau, the timing and geodynamic drivers for surface uplift of the central plateau remain poorly constrained. Here, we used both carbonate clumped isotope geothermometry and modified stable isotope-based paleoaltimetry that considers proportional mixing of two major moisture sources to infer late Eocene paleoelevations of the Nangqian Basin in the east-central Tibetan Plateau. The mean clumped isotope temperature, T(Delta(47)), of minimally altered late Eocene lacustrine carbonates is 30.0 degrees C, and the reconstructed least-evaporated paleowater delta O-18(mw) value is -9.8 parts per thousand. These two independent approaches indicate that during late Eocene time, the Nangqian Basin floor was 2.7 (+0.6/-0.4) km above sea level, and the hypsometric mean elevation of surrounding mountains was 3.0 +/- 1.1 km above sea level. These estimates are 1.1-1.2 km lower than their modern counterparts. The moderate to high late Eocene paleoelevation of the Nangqian Basin suggests that Eocene upper-crustal shortening and thickening can explain most, but not all, of the surface uplift of the east-central Tibetan Plateau. The additional 1.1-1.2 km (at most) of post-late Eocene elevation increase to the present height may have been a result of either lower-crustal flow or slab detachment.