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IGT Seminar- Using couple plate-mantle models to investigate subduction in the Neotethys Ocean
February 26, 2016 @ 4:00 pm - 5:00 pmFree
The geology of Tibet suggests that, prior to the collision of India with Asia, the Neotethys Ocean between the two continents was subducting via two, roughly parallel, northward-dipping subduction zones. Greater India may have initially collided with a volcanic arc above an inter-oceanic subduction zone before docking with the Eurasian Plate. This hypothesis is supported by seismic tomography studies, which image seismically fast structures at mid-mantle depths; these structures are commonly interpreted as cold, dense subducted slabs. Increased resolution and more data input into seismic tomography reveals distinct fast anomalies in the mantle beneath India, which are interpreted as originating at more than one subduction zone.
We use a global plate motion model, provided by the University of Lausanne, as the surface boundary condition of a 3D, spherical geometry mantle convection model to investigate the mantle structure produced by sub-parallel, simultaneous subduction prior to the collision of India and Asia. After 300 million years of convection driven by surface tectonics, we find a reasonable match between the modelled mantle structure and the structure imaged by seismic tomography, including distinct cold/fast anomalies associated with each of the subduction zones. We suggest that the mismatch between the modelled and imaged mantle structure may be used to refine plate motion models and locate now extinct plate boundaries with better precision. Such models could also be used to test plate reconstructions in tectonically complex areas, such as the cordilleran orogen in western North America or the Caribbean.
Our relatively simple coupled plate-mantle model can also be used to draw conclusions on the nature of subduction, such as why two northward-dipping parallel subduction zones are imaged in mantle tomography as appearing to have oppositely-dipping slabs down to mid-mantle depths.