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India-Asia Collision: drips, drops but no upper-mantle slabs


IPGP - Îlot Cuvier


Séminaires thème Intérieurs de la Terre et des planètes

Salle 310

David Rowley

University de Chicago

The current dominant paradigm for the crust and lithospheric evolution of the India-Asia collision in the Himalaya and Tibet is that they are shortened and thickened together, hence that their thicknesses are correlated. This paradigm also argues that changes in mantle lithospheric thickness are correlated with significant (up to 2 km) of elevation change above regions of convectively removed thickened lithosphere. New high resolution images of lithospheric mantle structure across India, Himalaya, and Tibet demonstrate that neither of these are true. Plateau topography remains unchanged across a >10% change in dVs anomaly in northern Tibet. Subduction dynamics, including subduction of the putative Greater Indian basin have been inferred, and slab-like structures have been interpreted beneath this region. High resolution imaging reveals no slabs in the mantle above 1000 km, but do image large volumes of irregularly shaped, drips, drops and flake-like bodies of seismically fast (≥1%) material in this volume of the mantle. Conversion of this fast material to lithospheric volume is compatible with > 4000 km of India-Asia convergence, equivalent to the post-initial collision of India with Asia at ~<60 Ma, and with eclogitic lower crust contributing to generate negative buoyancy to destabilize converging lithosphere under Tibet. Also on Zoom: