Geoid low and highs of the Indian Ocean and Western Pacific: Implications to mantle convection

The geoid highs of the Western Pacific coincide with the subduction zones in this sector. Its spectral analysis provided average depths to the large wavelength sources as ∼2335, ∼845 and ∼523 km. They are attributed to sources above D″ layer, and the transition zones in the upper-middle mantle within the error limit of 10-15% depending on the wavelengths. Deeper level of sources for the geoid highs of Pacific Ocean may be attributed to high angle of subduction in this sector where cold subducting slab of high velocity and density can get easily detached and sink into the lower mantle. In this case due to high angle of subduction of oceanic lithosphere, the subducting slab would be at lower temperature compared to surroundings maintaining it brittle even in the transition zone that has given rise to deep focus earthquakes almost up to 700 km. The high angle subduction along the subduction zones in the Western Pacific causes faster subduction that drives the Pacific plate faster (∼4-10 cm/year). In this case, the dehydration of the subducting slab would set in whole mantle convection between the lower and the upper mantle in the back arc regions of the mantle wedge. It has plausibly given rise to extensional regime forming back arc basins on large scale such as Japan Sea, Philippine Sea, Lau basin and others.