Predicting the origin of the Indian Ocean Geoid Low from global mantle convection models since the Cretaceous.

The origin of Earth's lowest geoid anomaly, the Indian Ocean geoid low, remains controversial. Previous studies attributed this geoid low to subducted fast velocity anomalies in the lower mantle. However, recent studies using seismic models suggest that high-density anomalies in the lower mantle alone fail to reproduce an isolated geoid low in the Indian Ocean, and low-density anomalies are required at mid to upper mantle depths. This study explores the origin of this elusive geoid low by employing plate reconstruction in global mantle convection models since the Cretaceous. Using a wide model parameter space, we control the rate of plume generation due to perturbation of the African LLSVP by lower mantle slabs. For example, we tested different values of Clapeyron slopes at 660 km, the effect of lateral viscosity variations, and the density of thermochemical piles, which eventually control the deformation of the LLSVPs. Our results demonstrate that the fit to the Indian Ocean geoid is poor, with only lower mantle slabs. However, when hot anomalies are also present at mid to upper mantle depths, the isolated geoid low is well reproduced. We also show that within the last 20Ma, as plumes ascend to mid to upper mantle depths beneath the Indian Ocean, the geoid low becomes more pronounced, though the slab structures remain the same, suggesting that hot anomalies play the dominant role in generating this isolated geoid low.