Integrated analysis of magnetic, gravity and multichannel seismic reflection data along a transect southeast of Sri Lanka, Bay of Bengal: New constraints

Abstract

Integrated analysis of high quality magnetic, gravity, bathymetry and multichannel seismic reflection data along a 1300 km long transect SK101 between the DSDP218/IODP1455 and ODP718 sites reveals the structure and evolutionary history of the underlying sedimentary load and basement. The smooth southward deepening bathymetry is pierced by several topographic highs of varying dimensions. Gravity does not mimic the bathymetry in general, and is as low as -75 mgal over a deep basement region. Magnetic anomalies depict significant variation along the transect, with chron A34 identified at its either end. Multichannel seismic reflection data reveal sediment thickness up to 3 s two-way travel time (TWT), but minimal (<0.1 s TWT) over protruding basement highs. Intense folding/faulting of sediment and basement producing low amplitude, long wavelength topographic highs is observed towards south along the transect. Flower structures seen within the sedimentary load suggest intermittent strike-slip faulting. The basement highs lying at the southern end of NW-SE trending fracture zones may have formed as the spreading center rotated clockwise during the Middle Cretaceous period. An arcuate gravity low is due to the presence of a deep and old basement, overlain by thick sediments. A prominent step in the basement coinciding with an abrupt change in magnetic anomaly pattern probably indicates the concurrent presence of oceanic crust of different ages, as a consequence of the Middle Cretaceous major plate reorganization.