INVESTIGATING THE TECTONIC ELEMENTS OF THE BENGAL BASIN, BANGLADESH USING GRAVITY, AND MAGNETIC DATA

The Bengal Basin is considered as one of the largest deltas located within 20°34′ to 26°38′ N latitude and 88°01′ to 92°41′ E longitude. The formation of the Bengal Basin begun with the counter-clockwise convergence between the Indian and Eurasian plates during the Miocene. The Bengal basin comprises a crucial geotectonic element of the Assam-Himalayan region. Based on the tectonic activity, crustal structures and landscape features the basin has been classified into three distinct elements. These are - the Indian Platform flank to the west, a deeper basin in the middle, and the folded belt in the east.

We have studied the influence of the variation of crustal dynamics and structures to understand the formation of sedimentary and structural features within the three tectonic zones. The research analyzed Bouguer gravity anomalies from the World Gravity Model 2012 generated by the Bureau of Gravimetrique International (BGI). Additionally, total magnetic intensity maps were derived from the inversion of gravity data.

Analysis of gravity, and magnetic mathematical derivative maps reveal anomalous zone at the central part of the basin. It is located below ~22 kilometers of sediment cover. Other gravity and magnetic highs were observed on the northeastern side correspond to the topographic high of the Shillong Massif. Additionally, we observe a gravity and magnetic low trending SW-NE, demarcating the division between the basin and the stable platform. In the northwestern stable platform, we could observe half-graben structures characterized by normal faults that could indicate the continental rifting during the Pangaean break-up. On the other hand, it is crucial to comprehend the gravity and magnetic features in the central basin, which is characterized by thick sedimentary cover. These magnetic highs indicate a source depth ranging from approximately 3 to 20 kilometers, with the deepest source depth observed at the central part of the basin. Comparatively, the northeastern side of the map, corresponding to the Shillong Massif, exhibits shallower source depth, which may have been influenced by the presence of the Dauki fault. Other than that, the eastern fold belt shows alternating high and low gravity and magnetic structures and an overall low due to the presence of thick sedimentary cover and a low magnetic attribute.