Deep low velocity layer in the sublithospheric mantle beneath India

Summary Globally, there is now a growing evidence for a low velocity layer in the deeper parts of the upper mantle, above the 410 km discontinuity (hereafter called LVL-410). The origin of this layer is primarily attributed to interaction of slabs or plumes with a hydrous mantle transition zone (MTZ) that results in dehydration melting induced by water transport upward out of the MTZ. However, the ubiquitous nature of this layer and its causative remain contentious. In this study, we use high quality receiver functions (RFs) sampling diverse tectonic units of the Indian sub-continent to identify Ps conversions from the LVL-410. Bootstrap and differential slowness stacking of RFs migrated to depth using a 3D velocity model reveal unequivocal presence of a deep low velocity layer at depths varying from 290 to 400 km. This layer appears more pervasive and deeper beneath the Himalaya, where detached subducted slabs in the MTZ have been previously reported. Interestingly, the layer is shallower in plume affected regions like the Deccan Volcanic Province and Southern Granulite Terrane. Even though a common explanation does not appear currently feasible, our observations reaffirm deep low velocity layers in the bottom part of the upper mantle and add to the list of regions that show strong presence of such layers above the 410 km discontinuity.