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Lithosphere Structure and upper mantle characteristics below the Bay of Bengal

Lithosphere Structure and upper mantle characteristics below the Bay of Bengal
Lithosphere Structure and upper mantle characteristics below the Bay of Bengal
The oceanic lithosphere in the Bay of Bengal (BOB) formed 80–120 Ma following the breakup of eastern Gondwanaland. Since its formation, it has been affected by the emplacement of two long N-S trending linear aseismic ridges (85oE and Ninetyeast) and by the loading of ca. 20-km of sediments of the Bengal Fan. Here, we present the results of a combined spatial and spectral domain analysis of residual geoid, bathymetry and gravity data constrained by seismic reflection and refraction data. Self-consistent geoid and gravity modeling defined by temperature-dependent mantle densities along a N-S transect in the BOB region revealed that the depth to the Lithosphere-Asthenosphere boundary (LAB) deepens steeply from 77 km in the south to 127 km in north, with the greater thickness being anomalously thick compared to the lithosphere of similar-age beneath the Pacific Ocean. The Geoid-Topography Ratio (GTR) analysis of the 85°E and Ninetyeast ridges indicate that they are compensated at shallow depths. Effective elastic thickness (Te) estimates obtained through admittance/ coherence analysis as well as the flexural modeling along these ridges led to the conclusions: i) 85°E Ridge was emplaced in off-ridge environment (Te = 10–15 km); ii) the higher Te values of ?25 km over the Afanasy Nikitin Seamount (ANS) reflect the secondary emplacement of the seamount peaks in off-ridge environment, iii) that the emplacement of the Ninetyeast Ridge north of 2°N occurred in an off-ridge environment as indicated by higher Te values (25-30 km). Furthermore, the admittance analysis of geoid and bathymetry revealed that the admittance signatures at wavelengths >800 km are compensated by processes related to upper mantle convection.
Lithospheric structure, Admittance, Geoid-Topography Ratio, Flexural modelling, Aseismic ridges, Upper mantle, Bay of Bengal
0956-540X
675-695
Srinivasa Rao, G.
631aab41-9b9f-4d1f-b8ba-de17dbf8dc77
Radhakrishna, M.
cde7116d-3c28-45dc-9706-b7f78a57e5ce
Sreejith, K.M.
77034a81-6b56-4940-81ee-50af66b3dd5c
Krishna, K.S.
fa339710-534a-4d69-9392-d83eddea9a76
Bull, J.M.
974037fd-544b-458f-98cc-ce8eca89e3c8
Srinivasa Rao, G.
631aab41-9b9f-4d1f-b8ba-de17dbf8dc77
Radhakrishna, M.
cde7116d-3c28-45dc-9706-b7f78a57e5ce
Sreejith, K.M.
77034a81-6b56-4940-81ee-50af66b3dd5c
Krishna, K.S.
fa339710-534a-4d69-9392-d83eddea9a76
Bull, J.M.
974037fd-544b-458f-98cc-ce8eca89e3c8

Srinivasa Rao, G., Radhakrishna, M., Sreejith, K.M., Krishna, K.S. and Bull, J.M. (2016) Lithosphere Structure and upper mantle characteristics below the Bay of Bengal. Geophysical Journal International, 206 (1), 675-695. (doi:10.1093/gji/ggw162).

Record type: Article

Abstract

The oceanic lithosphere in the Bay of Bengal (BOB) formed 80–120 Ma following the breakup of eastern Gondwanaland. Since its formation, it has been affected by the emplacement of two long N-S trending linear aseismic ridges (85oE and Ninetyeast) and by the loading of ca. 20-km of sediments of the Bengal Fan. Here, we present the results of a combined spatial and spectral domain analysis of residual geoid, bathymetry and gravity data constrained by seismic reflection and refraction data. Self-consistent geoid and gravity modeling defined by temperature-dependent mantle densities along a N-S transect in the BOB region revealed that the depth to the Lithosphere-Asthenosphere boundary (LAB) deepens steeply from 77 km in the south to 127 km in north, with the greater thickness being anomalously thick compared to the lithosphere of similar-age beneath the Pacific Ocean. The Geoid-Topography Ratio (GTR) analysis of the 85°E and Ninetyeast ridges indicate that they are compensated at shallow depths. Effective elastic thickness (Te) estimates obtained through admittance/ coherence analysis as well as the flexural modeling along these ridges led to the conclusions: i) 85°E Ridge was emplaced in off-ridge environment (Te = 10–15 km); ii) the higher Te values of ?25 km over the Afanasy Nikitin Seamount (ANS) reflect the secondary emplacement of the seamount peaks in off-ridge environment, iii) that the emplacement of the Ninetyeast Ridge north of 2°N occurred in an off-ridge environment as indicated by higher Te values (25-30 km). Furthermore, the admittance analysis of geoid and bathymetry revealed that the admittance signatures at wavelengths >800 km are compensated by processes related to upper mantle convection.

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More information

Submitted date: 4 August 2014
Accepted/In Press date: 20 April 2016
e-pub ahead of print date: 25 April 2016
Published date: July 2016
Keywords: Lithospheric structure, Admittance, Geoid-Topography Ratio, Flexural modelling, Aseismic ridges, Upper mantle, Bay of Bengal
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 393465
URI: http://eprints.soton.ac.uk/id/eprint/393465
ISSN: 0956-540X
PURE UUID: 7bc9224c-ae11-43a5-9d63-be89ee55db12
ORCID for J.M. Bull: ORCID iD orcid.org/0000-0003-3373-5807

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Date deposited: 27 Apr 2016 14:12
Last modified: 15 Mar 2024 02:44

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Contributors

Author: G. Srinivasa Rao
Author: M. Radhakrishna
Author: K.M. Sreejith
Author: K.S. Krishna
Author: J.M. Bull ORCID iD

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