Early Cretaceous fracture zones in the Bay of Bengal and their tectonic implications: Constraints from multi-channel seismic reflection and potential field data

摘要

Due to the lack of clearly discernible magnetic anomaly identifications and fracture zones in the Bay of Bengal (BOB), the early Cretaceous plate reconstruction history of eastern Gondwanaland remains an unresolved issue with regard to the separation of the East Coast of India from the conjugate Enderby Basin of Antarctica. Based on the correlation of oceanic basement information obtained from a vast amount of deep reflection seismic data, we identified 16 NW-SE-trending fracture zones (FZ1-FZ16) in the BOB region. The trends of these fracture zones at the ECMI indicate two distinctly different sets, one set in the direction ~N25°W to N35°W in the southern part (FZ1-FZ7) and the other set in ~N50°W (FZ8-FZ15) direction along the northern part. These two sets of fracture zones further support the earlier inferences about the segmented nature of the ECMI into southern sheared/oblique rifted margin and the northern normal rifted margin. While, the southern part of the ECMI had formed under slow/asymmetric spreading and mixed transform setting with its conjugate western Enderby Basin, the northern part of the ECMI formed after the breakup of the Elan Bank from India at M2. Considering this scenario, we infer the presence of Late Mesozoic (younger to M4) anomalies along the ECMI and the subdued nature of magnetic anomalies in the western BOB can be explained by the obliquity of fracture zones with respect to the coast, as observed in many marginal smooth zones of the world oceans. The disposition of the 85°E ridge with respect to the pre-evolved BOB crust and early Cretaceous volcanic episodes in the region together indicate an emplacement of the ridge from ~105. Ma onwards as a result of a hotspot source related to the Kerguelen super plume during its intense eruption activity.