The Indian ocean gravity low: Evidence for an isostatically uncompensated depression in the upper mantle

Ihnen, S. M.; Whitcomb, James H.

doi:10.1029/gl010i006p00421

Cited by 19 publications

(5 citation statements)

References 14 publications

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“…Most of the geoid lows have been linked to past subduction (Chase & Sprowl, 1983;Hager & Richards, 1989;Richards & Engebretson, 1992;Steinberger, 2000) as well as subduction coupled with mantle upwellings (Spasojevic et al, 2010). Several theories have been put forward to explain this negative anomaly, 10.1002/2017GL075392 such as depression of the core-mantle boundary (Negi et al, 1987), isostatically uncompensated crust (Ihnen & Whitcomb, 1983), and presence of paleo back-arc basins in the Neo-Tethys Ocean prior to India's collision with Eurasia (Nerlich et al, 2016). A recent study by Reiss et al (2017) found a hot midmantle anomaly beneath the Indian Ocean geoid low (IOGL) and concluded that this high-temperature anomaly along with cold material below 660 km farther south could be responsible for the geoid low.…”

Section: Introductionmentioning

confidence: 99%

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

Ghosh

Thyagarajulu

Steinberger

2017

Geophysical Research Letters

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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 ∼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.

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Section: Introductionmentioning

confidence: 99%

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

Ghosh

Thyagarajulu

Steinberger

2017

Geophysical Research Letters

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“…Probably, one of the locations of mass deficiency is at the core-mantle boundary (Hide and Malin, 1970;Negi et al, 1987;Padma Rao et al, 2017), and the other within the mantle (Kaula, 1972). According to Ihnen and Whitcomb (1983), the IOGL is caused by a sag in the crustal boundary whereas Marsh (1979), and Mishra et al (2004) opined as due to low-density rocks in the upper mantle (Mishra, 2014;. The IOGL is caused by a low-density anomaly stretching between the depth of 300 km and ~900 km in the northern Indian Ocean (Ghosh et al, 2017;Reiss et al, 2017) while Chase (1979) suggested approximately 1200 km.…”

Section: Geoid Anomalymentioning

confidence: 99%

Gravity Anomalies, Isostasy and Density Structure of the Indian Continental Lithosphere

2020

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Gravity anomalies across the Indian region depict most of the geological and tectonic domains of the Indian continental lithosphere, which evolved through Archean cratonic nucleation, Proterozoic accretion, Phanerozoic India-Eurasia plate convergence, and modification through many thermal perturbations and rifting. Integrated analysis of gravity and geoid anomalies together with topographic and heat flow data led to deciphering the mechanism of isostatic compensation of topographic and geological loads, lithospheric structure, and composition. This study discusses the nature of gravity (free-air, Bouguer and Isostatic) and geoid anomalies in relation to the topography, geology, and tectonics, and presents a lithospheric density model across the peninsular India and Himalaya. Southern peninsular Indian region shows relatively low Bouguer gravity anomalies compared to the northern region. The mobile belts are generally observed to have relatively higher Bouguer gravity anomalies, e.g., Eastern Ghats Mobile Belt compared to the shield regions. The gravity lows are observed over topographic features like the Western Ghats and Himalaya, while some of the topographic highs like Aravalli show positive gravity anomaly. The Indian Ocean Geoid Low varies from -82 m over Dharwar Craton to -98 m over the Southern Granulite Terrain and finally reaches a significant low of -106 m in the Indian Ocean. Flexural isostatic compensation with variable Effective Elastic Thickness (EET) ~10 km to 50 km prevails over the stable continental region. The lithospheric thickness varies from 80 km along the coastal region to 120-130 km beneath the Saurashtra Plateau, the Southern Granulite Terrain, and the Eastern Indian Shield, and reaches to more than 200 km under the Himalayan orogenic belt in the north. From Dharwar Craton to Bundelkhand Craton in central India, the lithospheric thickness varies between 160 and 180 km.

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“…Different theories were put forward to explain this negative geoid anomaly. Uncompensated crust (Ihnen & Whitcomb, 1983), CMB deflection (Negi et al., 1987), lower mantle slabs (Rao & Kumar, 2014), mantle upwelling due to dehydration of subducted Mesozoic slabs (Spasojevic et al., 2010), presence of hot low‐velocity anomaly in mid to upper mantle depths (Ghosh et al., 2017) and superposition of high and low‐velocity anomalies beneath the Indian Ocean (Paul & Kumar, 2022; Rao et al., 2020; Steinberger et al., 2021) were all suggested as possible mechanisms. All these studies looked at the present‐day anomaly and were not concerned with how this geoid low came into existence.…”

Section: Introductionmentioning

confidence: 99%

How the Indian Ocean Geoid Low Was Formed

Pal

Ghosh

2023

Geophysical Research Letters

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The origin of the Earth's lowest geoid, the Indian Ocean geoid low (IOGL) has been controversial. The geoid predicted from present‐day tomography models has shown that mid to upper mantle hot anomalies are integral in generating the IOGL. Here we assimilate plate reconstruction in global mantle convection models starting from 140 Ma and show that sinking Tethyan slabs perturbed the African Large Low Shear Velocity province and generated plumes beneath the Indian Ocean, which led to the formation of this negative geoid anomaly. We also show that this low can be reproduced by surrounding mantle density anomalies, without having them present directly beneath the geoid low. We tune the density and viscosity of thermochemical piles at core‐mantle boundary, Clapeyron slope and density jump at 660 km discontinuity, and the strength of slabs, to control the rise of plumes, which in turn determine the shape and amplitude of the geoid low.

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The Indian ocean gravity low: Evidence for an isostatically uncompensated depression in the upper mantle

Cited by 19 publications

References 14 publications

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

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

Gravity Anomalies, Isostasy and Density Structure of the Indian Continental Lithosphere

How the Indian Ocean Geoid Low Was Formed

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