Structure of the Earth's Crust and Tectonic Evolution of the Central Bengal Basin

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Abstract

A comprehensive analysis of geological and geophysical data characterizing the structure of the Central Bengal Basin (CBB) and its framing structures was carried out. For the first time, a submeridional section of the deep seismic sounding crossing the CBB was presented. It is found that the consolidated crust in the CBB has a complex block structure. The velocity characteristics of the basement and the gradient two-layer structure of the upper mantle unambiguously indicate that the basin was formed on continental rather than oceanic crust. The mechanism of the CBB basement sinking, the amplitude of which reaches 11 km, may be the compaction of the basic rocks of the lower part of the continental crust at its contact with the heated upper mantle and the transition of gabbroid rocks into eclogites with density of (3.6 g/cm3) which is higher than that of mantle peridotites (3.3 g/cm3). We conclude that the CBB, the 85° E Ridge, and the Bengal sector of the East Indian Ridge are relict fragments of the differentially submerged eastern part of the Indian paleocontinent.

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About the authors

V. K. Illarionov

Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences

Author for correspondence.
Email: vkillar@mail.ru
Russian Federation, Moscow

O. Yu. Ganzha

Shirshov Institute of Oceanology of the Russian Academy of Sciences

Email: vkillar@mail.ru
Russian Federation, Moscow

D. A. Ilyinsky

Shirshov Institute of Oceanology of the Russian Academy of Sciences

Email: vkillar@mail.ru
Russian Federation, Moscow

K. A. Roginsky

Shirshov Institute of Oceanology of the Russian Academy of Sciences

Email: vkillar@mail.ru
Russian Federation, Moscow

L. D. Fleifel

Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences

Email: vkillar@mail.ru
Russian Federation, Moscow

A. Yu. Borisova

Institute of Geological and Environmental Sciences

Email: vkillar@mail.ru
France, Toulouse

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Supplementary files

Supplementary Files
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2. Fig. 1. Depth map of the acoustic basement of the BR, isohypses, km ([4] with ext.). The map shows the main structural-tectonic taxa of the basement of the BR and the scheme of geological and geophysical study of its central part. I - structural-tectonic taxa of the first order: 1 - Central Bengal Basin, 2 - 85° E. Ridge, 3 - East Indian Ridge, 4 - Jessor Depression, 5 - Western Basin, 6 - East Indian Plateau, 7 - "structural shaft", 8 - South Sri Lankan Basin; II - seismoacoustic beacons, in the numerator is the velocity of seismic waves in the basement, in the denominator - the depth of occurrence of its roof [29]; III - CDP profiles: MAN1, MAN3 (MV Sagar Sandhani, [30]), SK 107-07 (ORV Sagar Kanya, [27]), MCS-I (IS Haiyandichi-9, R.V. Haiyangdizhi-9, 2019 [35]), GSZ profiles M3, M4 (NIS Mezen, 2003); IV - GSZ profiles 2, 5, 11 [36]; V - deep-water drilling wells of the DSDP project; VI - well of the IODP-1444 project; VII - industrial drilling wells; VIII - epicentres of modern earthquakes [23].

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3. Fig. 2. Regional latitudinal DOM-OGT transects (a-c) characterising the seafloor structure of the Bay of Bengal. The vertical scale gives the double travelling time of the reflected wave. See Fig. 1 for the position of the profiles. Notation: WB - Western Basin; 85°E - 85°E Ridge; CBB - Central Bengal Basin; EIH - East Indian Ridge; jagged line - oceanic basement, according to [32].

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4. Fig. 3. Gravimetric map of the BR in the Bouguer reduction [by 33 (c supplementary)]. Numbers in circles: 1 - Central Bengal Basin, 2 - East India Ridge, 3 - 85°E ridge. Dotted lines indicate CDP profiles; solid lines are GSS profiles: M-1, M-2, M-3, M-4, M-5 (NIS ‘Mezen’); GSZ profiles: Pr-2, Pr-5, Pr-11 [36].

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5. Fig. 4. Buried carbonate bank at the top of the Ridge 85°E [20].

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6. Fig. 5. Denuded surface of one of the hill blocks of the 85°E ridge, on which fragments of carbonate sediments are preserved [20].

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7. Fig. 6. a - Graph of the gravity anomaly with reduction in free air [34]. The alternation of maxima and minima of the curve are well correlated with the block structure of the consolidated crust; b - depth velocity model of the Central Bengal Basin based on the GSZ M-3 profile. The profile position see Fig. 1. Solid lines - boundaries plotted along the refractive sites 1-D of the velocity columns. Black figures - velocity at the roof of the layer. Red figures - velocity at the bottom of the layer. Vertical dashed lines - block boundaries plotted by the change of velocities at the roof and bottom of the layer. Dashed line - assumed continuation of M2 boundary. LCL - lower crustal layer with anomalously high velocity.

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8. Fig. 7. Latitudinal geological-geophysical section constructed taking into account GSZ data migrated to the time domain and DOM-OGT. The section along profile SK 107-07 is taken as a reference section: 1 - water layer; 2 - sedimentary layer; 3 - volcanogenic-sedimentary layer; 4 - basement composed of continental crust; 5 - Moho M1; 6 - Moho M2.

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