GEOPHYSICAL CHARACTERIZATION OF CRUSTAL STRUCTURES AND TECTONIC FRAMEWORK OF THE BENGAL BASIN, BANGLADESH USING GRAVITY, AND MAGNETIC DATA

The Bengal Basin stands as one of the largest depositional systems serving as a remnant ocean basin of the Himalayas. Its inception is traced back to the collision between the Indian and Eurasian plates. Since the formation, the basin has characterized as a significant geotectonic element of the Assam-Himalayan region, encompassing three distinct tectonic elements: (1) the Indian Platform flank to the west, (2) a deeper basin in the middle, and (3) the folded belt in the east, each characterized by its unique sedimentary scheme.

One must consider the influence of crustal dynamics and deep crustal structures during both syn- and post-collisional periods to comprehend the formation of sedimentary and structural features within the deeper basin and active fold belt. This study investigates these deep crustal structures using gravity and magnetic data to gain insights into their impact on the various tectonic elements.

The research analyzed Bouguer gravity anomalies from the World Gravity Model 2012 provided by the Bureau of Gravimetrique International. Additionally, total magnetic intensity maps were examined, derived from the inversion of gravity data. The study area was confined within the geographical boundaries of 20° to 27° N latitude and 84° to 94° E longitude.

The analysis of gravity, magnetic, and mathematical derivative maps reveal a deep-seated anomalous zone with higher values at the central part of the basin. This zone is concealed beneath ~22 kilometers of sediment. Furthermore, gravity and magnetic highs observed on the northeastern side correspond to the topographic high of the Shillong Plateau. Additionally, we observe a gravity and magnetic low trending SW-NE, demarcating the division between the basin and the stable platform. These gravity and magnetic highs and lows provide insights into the local structural distribution. However, the focus of the study revolves around comprehending the gravity and magnetic highs in the central basin, 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 basin, corresponding to the Shillong Plateau, exhibits shallower source, likely influenced by the presence of the deep-seated structures and the presence crystalline rocks.