Morphotectonic characteristics of the Andaman volcanic arc and its adjoining regions, Andaman Sea

Abstract

The oblique subduction of the Indian Plate beneath the Sunda Plate has resulted in the formation of diverse morphotectonic structures and major changes to the seafloor topography in the Andaman Sea, northeastern Indian Ocean. Inner volcanic arc, sliver fault system, narrow oceanic basins and backarc basins are the principal morphotectonic elements that influenced the tectonic setting and geodynamics of the Andaman backarc region. The volcanoes and fault systems in Myanmar and Sumatra are well studied, but we know relatively less about the morphotectonics of the submarine volcanoes and sliver fault networks in the Andaman Sea, that connect the volcanoes and fault systems in Myanmar and Sumatra. In the present study, we compiled the all-available high resolution bathymetry data which covers an area of approximately 140,000 km² in the Andaman backarc region and provided a detailed morphotectonic analysis of each of the tectonic elements. The data show 33 submarine volcanoes of varying dimension in the Andaman Sea, that stretches from the dormant Narcondam volcano to the north of Sumatra Island. In addition, the major fault systems such as Great Sumatra Fault, West Andaman Fault and Andaman Nicobar Fault that starts from northern Sumatra and ends with Andaman Backarc Spreading Centre delineated from the high-resolution bathymetry data are analysed. Northward extension of the Great Sumatra Fault furcates into several branches, which produce narrow oceanic basins. The existence of submarine volcanoes situated in the middle of these basins indicate that the Andaman-Nicobar-Sumatra volcanic arc traverses through this narrow basinal area. The occurrence of well-developed cratered volcanoes, frequent earthquake swarms and gas emanations through the flanks of the cratered seamount suggest that the off Nicobar region between 6ºN to 8ºN is the most active part of the volcanic arc during the recent past.