Has the Tibetan Plateau risen in the Early/Mid-Miocene? Constraints from plate-motion reconstructions and seismicity of the Indian Ocean lithosphere

Abstract

SUMMARYMagnetization records and seismic stratigraphy of the Indian Ocean lithosphere indicate that the Early/Mid-Miocene onset of diffuse contractional deformation coincided with slowdowns of the Indian and Capricorn plate motions. At present day, such deformation is evidenced by the seismicity of the Indian Ocean floor. Deformation onset and past plate-motion slowdowns have been interpreted as consequences of a sudden uplift of the Tibetan Plateau by 1–2 km, as this—following previous estimates—would generate a tectonically significant force between 4 × 1012 and 8 × 1012 N m−1. However, this view remains at odds with palaeoaltimetry estimates from geological and geochemical data, which indicate no increase in plateau altitude throughout the Miocene. Here, I use well-established models of viscous/brittle dynamics in inverse mode in order to constrain the amount of force that should be delivered by the Tibetan region to the Indian tectonic setting in order to explain the observations above. Results constrain such a force within the range from 4.3 × 1011 to 3.5 × 1012 N m−1. By comparison with previous estimates of the force associated with topography increase, these analyses suggest that the Early/Mid-Miocene onset of contractional deformation and plate-motion slowdowns within the Indian Ocean require minimal uplift of the Tibet Plateau of a few hundred metres. The seemingly contradicting inferences on Early/Mid-Miocene Tibetan uplift that come from geophysical and geological/geochemical observations can be reconciled by noting that the required uplift amount is less than what is resolvable by modern palaeoaltimetry techniques.