Paleoelevation of the Tibetan Plateau Relative to Plate Convergence, Crustal Shortening and Conservation of Crustal Mass

Abstract:

Topographic evolution can be used to infer geodynamic processes involved in orogensis. But, for a long time, the topographic history of the Tibetan orogen has remained controversial because of competing ideas of how the proxy record for elevation is interpreted and how exactly topography change can be related to geodynamic processes. Mounting evidence in the structural record across northern and eastern Tibet calls for the onset of crustal shortening to either precede or closely follow the ~ 50 Ma continental collision. Surficial records of climate proxies for paleoelevation also have been interpreted as the development of modern elevation of the Tibetan Plateau at an early stage in orogenesis. However, if the attainment of early high-elevation is reflective of achieving modern crustal thicknesses, then much of the continental convergence in the last 30-40 Myr did not contribute to thickening the Asian crust and as such, produces a paradox of missing crustal mass within the orogen. So, if modern elevations were reached in early Cenozoic time, we should be concerned with the mechanisms by which crust can be removed from the convergent system in large quantities. Alternatively, early deformation could produce local topography and proxy records could record these local elevation changes rather than the attainment of regional high topography.