Abstract:
Ocean bottom magnetometer (OBM) investigations were made across the Ninetyeast Ridge in the Bay of Bengal and geomagnetic field variations were recorded for a period of about one month. Analysis of data indicates that the thickness as well as resistivity of the oceanic crust/upper mantle reduces from 17 - 14 km and 439 - 308 Ohm-m respectively, as one moves from the Bay of Bengal to the Andaman are region. The highly conducting Andaman are region may have formed due to subduction related processes at the Andaman trench. Analysis of OEM data collected earlier across the Barren Island in the Andaman Sea indicates the presence of two conductivity zones, at 17 - 27 km and 80 - 100 km depth. The enhanced conductivity at a shallow depth may be due to the conducting material/magma that has been emplaced by upwelling of the mantle material at the tectonic zone. The thickness of this material increases from north to south of the Barren Island and seems to concentrate the induced currents within the island. The enhanced conductivity at greater depths may be due to the H2O and CO2 that may be released by metamorphic reactions of the subducting Indian plate beneath the Burmese plate.
