The Importance of Upper Mantle Heterogeneity in Generating the Indian Ocean Geoid Low

One of the most pronounced geoid lows on Earth lies in the Indian Ocean just south of the Indian peninsula. Several theories have been proposed to explain this geoid low, most of which invoke past subduction. Some recent studies have also argued that high-velocity anomalies in the lower mantle coupled with low-velocity anomalies in the upper mantle are responsible for these negative geoid anomalies. However, there is no general consensus regarding the source of this particular anomaly. We investigate the source of this geoid low by using models of density-driven mantle convection. Our study is the first to successfully explain the occurrence of this anomaly using a global convection model driven by present-day density anomalies derived from tomography. We test various tomography models in our flow calculations with different radial and lateral viscosity variations. Some of them produce a fairly high correlation to the global geoid, but only a few (SMEAN2, GyPSuM, SEMUCB, and LLNL-JPS) could match the precise location and pattern of the geoid low in the Indian Ocean. The source of this low stems from a low-density anomaly stretching from a depth of 300 km down to similar to 900 km in the northern Indian Ocean region. This density anomaly potentially originates from material rising along the edge of the African Large Low Shear Velocity Province and moving toward the northeast, facilitated by the movement of the Indian plate in the same direction. Plain Language Summary One of the lowest geoid anomalies on Earth lies in the Indian Ocean just south of the Indian peninsula. Several theories have been proposed to explain this gravity low. Most of these theories try to explain the existence of this anomaly with the help of cold, dense oceanic plate that sank into the mantle in the past and which could potentially be present below the Indian Ocean at depths greater than 1,000 km. However, there is no general consensus regarding the source of this particular negative geoid anomaly. We investigate the source of this low by using models of density-driven mantle convection. Our study finds that the source of this low stems from a low-density anomaly stretching from a depth of 300 km down to similar to 900 km in the northern Indian Ocean region. This density anomaly potentially originates from hot buoyant material rising from deep mantle beneath Africa and moving toward the northeast, facilitated by the movement of the Indian plate in the same direction. Our study is the first to successfully explain the occurrence of this geoid low using present-day density anomalies.

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