285-3 Response of the Tibetan Plateau to the Underthrusting Indian Lithosphere: Implications for Crustal Deformation

Session: Rock Deformation and the Dynamics of Mountain Building: A Session Honoring the Scientific Contributions of John P. Platt, Part II

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We propose that the mantle lithospheric density and crustal thickness are correlated in such a way as to produce a flat Tibet plateau. We observe that the mantle lithosphere is relatively uniform beneath the Himalaya and southern and central Tibet, despite a near doubling of crustal thickness relative to India. Farther north, cratonic mantle lithosphere disappears over large regions of north-central Tibet giving rise to large lateral variations in uppermost mantle Vs anomalies (>12%) that are uncorrelated with changes in surface elevation but are closely related to changes in crustal thickness. This decoupling of surface topography from spatial variations in upper mantle seismic velocity, and assumed buoyancy, implies Tibetan topography is controlled by a crust-mantle interaction that is able to maintain its near constant elevation. This crust-mantle interaction is likely driven by gravitational potential energy with a very weak crust.  This is consistent with a variety of studies that have all pointed to an extremely weak Tibetan crust that is essentially able to flow over short term geologic time.  Magmatism, with ages of ~20 Ma to Present, spatially correlated with this region with no sub-Moho mantle lithosphere imply destabilization of mantle lithosphere in northern Tibet. Cratonic Indian underthrusting for the past 25 Ma has also not led to significant topography in the Plateau through time. The magmatism may have helped weaken the crust allowing the crust to respond to changes in uppermost mantle buoyancy resulting in a flat Plateau.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5319

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