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Appraisal of lineaments patterns and crustal architectures around the Owen fracture zone, Arabian Sea, using global gravity model data

Narayan Satya, Kumar Ujjawal, Sahoo Soumyashree Debasis, Pal Sanjit Kumar

Acta Geophysica

2024

Vol. 72, no. 1

29--48

This study evaluates the efficacy of GECO gravity data for geophysical studies, mapping structural and tectonic features and their impact on gravity signatures in the study area. Computed correlation coefficient (96-98%), root-mean-square error (5.1-5.3 mGal), and standard deviation (3.9-4.2 mGal) between the GECO model-derived and ship-borne free-air gravity reveal the efficacy of the GECO gravity data for the geophysical studies in the region. A total horizontal derivative approach was used in order to enhance the residual and regional responses of the Bouguer gravity anomaly. The shorter-wavelength lineaments originated from subsurface mass heterogeneities were found trending in the northwest direction, subsequently east, north-northeast and east-northeast directions. In contrast, the longer-wavelength lineaments originating from deep-seated mass heterogeneities dominated in the east-northeast direction, followed by north-northeast and northwest directions. Lineaments occurring at shallower depths are associated with sedimentary/basement columns and could be utilised in basin demarcation for hydrocarbon exploration. In contrast, deep-seated lineaments originated due to deformities at the crust-mantle boundary or in the mantle and could be used in the region’s seismicity analysis. Spectral analysis and 2D forward modelling results indicate sediment thickness of ~ 2.0-6.0 km, basement thickness of ~ 6-14 km, and Moho depth of ~ 10-18 km. Delineated lineaments and computed basement and Moho depths were further validated with existing data. Anomalously high and low gravity features were interpreted based on Moho depth, basement thickness, and sediment thickness. This study concludes that anomalous gravity anomalies are mainly controlled by Moho topography despite the relatively thicker crust in the northern region. The crustal thickness mainly controls the southern latitude’s gravity signatures.

New insights into the structural and tectonic settings of the Bay of Bengal using high resolution earth gravity model data

Narayan Satya, Kumar Ujjawal, Pal Sanjit Kumar, Sahoo Soumyashree Debasis

Acta Geophysica

2021

Vol. 69, no. 6

2011--2033

The residual anomaly of GECO model-derived gravity data has been enhanced using first vertical derivative, tilt derivative and balanced horizontal derivative for delineation of structural and tectonic features over the Bay of Bengal (BOB). Entire BOB basin is classified in eastern, central and western basins for analysis of the delineated lineaments to understand the tectonic setting. It is observed that major lineament trends in the western and central basins are N–S, NE–SW, and in the eastern basin N–S, NNE–SSW, while prominent lineament trend for the entire BOB basin is in N–S direction. The statistical analysis of the lineament attributes, viz. lineament density, circular standard deviation, circular variance for the lineaments, reveals that the crust under the central basin has experienced the maximum tectonic disturbances followed by the western and the eastern basins. Euler depth solutions for structural index (SI) zero estimate the possible source depths of the lineaments as (i) 3.0–9.0 km (possibly top sedimentary layer), (ii) 9.0–18.0 km (possibly intermediate sedimentary layer), (iii) 18.0–24.0 km (possibly upper crustal layer), (iv) 24.0–33.0 km (possibly lower crustal layer) and (v) 33.0–64.0 km (possibly associated with Lithosphere). Power spectral analysis and 2D forward modelling indicate that sediment thickness varies from 2.0 to 17.0 km; crustal thickness varies from 4.0 to 16.0 km, and Moho varies from 10 to 34 km depth over the BOB. The present study confirms that the origin of the 85°E ridge is due to the sagging of ridge crust into the mantle lithosphere, whereas the NER has a hotspot origin.