Seismic Evidence for a Hot Mantle Transition Zone Beneath the Indian Ocean Geoid Low

Abstract

The Indian Ocean Geoid Low (IOGL) is the most prominent geoid anomaly (−106 m) on the globe, whose origin remains elusive. In the present study, we investigate the mantle transition zone (MTZ) structure beneath the region using P receiver functions (PRFs), to examine its role in the genesis of this feature. Results from 3‐D time to depth migration of PRFs reveal a thin MTZ primarily due to an elevation of the 660 km discontinuity. This is suggestive of anomalously hot temperatures in the mid mantle beneath the IOGL region, possibly sourced from the African Large Low Shear Velocity Province (LLSVP). The combined effect of the hot (low‐density) material in the MTZ proposed in this study and the (high‐density) cold slab graves atop the core‐mantle boundary inferred from previous studies can possibly explain this geoid low.

The Indian Ocean Geoid Low at a plume-slab overpass

“…The narrower geoid high (Figure 4) appears, relatively, most prominently for a comparatively thin streak and in cases where the anomaly is restricted to shallow depth. The fact that the actual geoid low does not feature a central high could indicate that the density anomaly is more prominent near the transition zone, as suggested in previous work (Reiss et al, 2017;Rao et al, 2020). The exothermic phase transition at around a depth of 410 km may further strengthen the effect of any temperature and density anomalies around that depth.…”

“…To date, various sources which could give rise to the IOGL have been proposed in the literature, including a low-density anomaly in the upper mantle (Reiss et al, 2017;Rao et al, 2020) and high-density anomaly in the lower mantle (Rao and Kumar, 2014), as both can cause a geoid low. Recently, Ghosh et al (2017) have shown that the IOGL can be explained well by mantle density anomalies inferred from seismic tomography, but the cause of these density anomalies was not thoroughly investigated.…”

“…Evidence for a hot midmantle anomaly in the area of the IOGL has also been reported by Reiss et al (2017) who used the differential travel times of PP, SS waves and their precursors. Additionally, Rao et al (2020) map a thin mantle transition zone from 3-D time to depth migration of P receiver functions.…”

INSA National Report on Seismological Research in India: 2019 – 2022

“…Tomography images also report subduction of Indian plate beneath the Burmese arc with signatures of a medium of high shear wave velocity below ∼ 50 km to ∼ 75 km depth. 2.4 Indian Ocean and Bay of Bengal Rao et al (2020) investigated the mantle transition zone (MTZ) structure beneath the Indian Ocean Geoid Low (IOGL) region using P-RFs. 3-D time-to-depth migration of P-RFs reveals a thin MTZ primarily due to an elevation of the 660 km discontinuity.…”

INSA National Report on Seismological Research in India: 2019 – 2022

“…Tomography images also report subduction of Indian plate beneath the Burmese arc with signatures of a medium of high shear wave velocity below ∼ 50 km to ∼ 75 km depth. Rao et al (2020) investigated the mantle transition zone (MTZ) structure beneath the Indian Ocean Geoid Low (IOGL) region using P-RFs. 3-D time-to-depth migration of P-RFs reveals a thin MTZ primarily due to an elevation of the 660 km discontinuity.…”