Mio-pliocene growth of the Tibetan Plateau and evolution of East Asian climate

During the past 15 years, numerous studies have reported not only ecological and climatic changes at 6- 8 Ma, but also the roughly concurrent onsets of tectonic processes in regions surrounding the Tibetan Plateau. The ecological changes corroborate suggestions of a switch to a more arid climate on the northern margin of the Indian subcontinent, which were first made by vertebrate paleontologists working in Pakistan. Some of the more recent observations extend the region of increased aridity north and northeast of Tibet. Moreover, some evidence suggests that near 8 Ma, the wind fields over the Arabian and South China Seas simultaneously became more like those of the present day, which are dominated by the Indian and East Asian monsoons, respectively. The onsets of tectonic processes, which in nearly all cases are less precisely dated than the ecological and climatic changes, could have occurred as responses to a similar to 1000- 2000- m increase in the mean elevation of the Tibetan plateau; a greater mean elevation of this amount should raise deviatoric compressive stresses on the margins of the plateau sufficiently to initiate deformation of these regions. The link between deep- seated tectonic processes and regional, if not global, environmental change is too tantalizing to ignore, but inconsistencies in timing and in mutual implications of the various observations by no means require such a link, or that such a change in Tibet's mean elevation occurred. I review the various observations objectively both to show the potential correlations and to expose these various inconsistencies.