Evidence for a new age constraint of the oceanic lithosphere of the Bay of Bengal

Abstract

Dating the age of oceanic crust in the Bay of Bengal presents a major challenge due to several geological complexities such as: i) most of the oceanic lithosphere was accreted during the Cretaceous Normal Superchron (120 - 83 Ma), ii) crust was affected by intense volcanic activity associated with the Kerguelen plume, and iii) the ocean floor is buried under copious amounts of Bengal Fan sediments (~ 4 – 18 km). A major plate reorganization that occurred during the mid-Cretaceous period disrupted tectonic patterns. As a result, the detachment history of micro-continents like Elan Bank from the East Coast of India has not been unambiguously revealed. In this study, we make use of variations in the Earth’s geomagnetic field strength that occurred during the Cretaceous Normal Superchron to identify internal magnetic markers, specifically Q1 (92 Ma) and Q2 (108 Ma), in the Bay of Bengal. Analysis of ship-borne magnetic profile data and magnetic regional model (EMAG2) of the Bay of Bengal and Western Enderby Basin, East Antarctica led us to recognize the internal time marker Q1, thereby 92 Ma age is assigned with greater confidence to the ocean floor of the Bay of Bengal located at around 12°N latitude between the 85°E and Ninetyeast ridges. Seismic reflection data indicate the presence of approximately 6 km thick, typical oceanic crust in this area, formed during the Q1 period between two buried volcanic ridges. The oceanic fracture zones termination in the vicinity of Q1 anomaly may possibly indicate the timing (92 Ma) of the plate reorganization in the Indian Ocean. This is the first time that, with more confidence, a 92 Ma age constraint has been provided for the Bay of Bengal region, and this finding enhances our understanding of the region's geological evolution and offers new insights into the tectonic history of the northeast Indian Ocean during the Late Cretaceous.