We present a brief, but precise description of the geodynamic evolution, and tectono-structural framework of the Bengal Basin. The tectonic map (Main Map) at 1:12,50,000 scale should be considered as a first attempt to provide a more comprehensive and accurate geotectonic cartography of the entire region, with respect to the available maps in the published literatures, and in the light of scientific advances in geodynamics, tectonics and structures reached in the last decades plus new geological field works carried out in some key sectors of the Bengal Basin. The tectonic map of the Bengal Basin improves the knowledge of the geometry of the basin boundary, tectonic settings and relevant structures, and its relation to the collision of the Indian and the Burmese plates. Three schematic geological cross-sections illustrate the tectonic architecture of the basin in depth as well as surroundings. The latest understanding of the present-day geodynamics would help to develop advanced kinematic and dynamic modelling of the Bengal Basin in relation to the pre- and post-collisional stages of the Indian Plate.

A clear insight of the Indo-Burma amalgamation is required for an understanding of the complex processes of the Indo-Asian collision. Where and when the northeastern part of the Indian subcontinent amalgamated with the Burma plate has not yet been well defined. In order to better understand the tectonic affiliations and evolution of the Indo-Burma Ranges (IBR), we report new detrital zircon U-Pb and Hf isotope data of nine sandstone/siltstone samples (late Miocene−Pliocene) from the Chittagong-Tripura Fold Belt, Bangladesh, which is in the Neogene belt of the IBR. Our results show that the zircon ages of all nine samples have three peaks at <200 Ma, ca. 500 Ma, and 800−1000 Ma. The percentage of young (<200 Ma) zircons increase from the Boka Bil Formation (6.9% to 15.2%) to the Tipam Formation (20.3% to 27.6%). The ε_Hf(t) of most young zircons from the Boka Bil Formation suggest derivation from the Gangdese arc, whereas those from the Tipam Formation show an affinity with the Burma magmatic arc. Therefore, we suggest that the increase of young zircons in the Tipam Formation came from the Burma plate. Comparing provenances of the Paleogene and Neogene belts of the IBR, we suggest that they belong to the Burma plate and Indian subcontinent, respectively, and that the Kaladan Fault, separating these two belts, is the suture between the Indian and Burma terranes. The time of amalgamation is constrained by the ca. 2.5−3.9 Ma boundary between the Boka Bil and Tipam formations, and the eastern Indian promontory likely collided with the Burma plate ca. 11−12 Ma.

The tectonic deformation of the outer Indo-Burman Ranges (i.e., Chittagong Tripura Fold Belt, CTFB) is associated with the oblique convergence of Indo-Burmese plates since the latest Miocene. This article presents detailed field evidence of deformation structures and their kinematics in the exposed Tertiary successions in the CTFB. We combine observations made in this study with the published structural, geodetic, and seismic data sets to present an overview of the active tectonic framework of the region and its strain partitioning. To determine the kinematic evolution, décollement depth, and amount of strain, we combined geologic field mapping, structural analysis of fifteen anticlines, fracture/lineament analysis, and paleostress analysis of faults that define the ∼100 km wide CTFB. Structural data and kinematic analyses suggest subhorizontal plane strain with approximately 10% east-west shortening (oriented ~65°) that is perpendicular to the axial plane (oriented ~155°) of the CTFB anticlines. No evidence of significant transpression or strike-slip faulting has been observed in the CTFB and, therefore, suggests that full slip-partitioning is normal to the outer belt and parallel to the inner belt of the IBR. Paleostress analysis results are in good agreement with the present-day stress regime, and this implies that past and present deformation is dynamically related with the normal component of India-Burma oblique vector velocity motion.