Abstract
Abstract Magnetotelluric studies over the Middle Andaman islands have delineated a NNE-SSW trending suture, along which the Andaman flysch and the underlying Igneous crust subduct eastwards along a high angle thrust with a dip angle of about 60°. The Andaman flysch, which have thickness varying between 4 and 10 km are delineated up to depth of about 17 km along the observed thrust. The crust to the west of the suture has a high resistivity of more than 10000 Ω-m, as against a moderate resistivity of about 1000 Ω-m observed in the eastern part. The complex variations in its thickness and resistivity are indicative of the intense tectonic activity that this juvenile crust has experienced since the Cretaceous. The crust is underlain by a low resistivity, which could be due to the presence of fluids generated by the metamorphosis of the subducting crust and also expelled from the rocks at deeper levels. However the earthquake focal depths, extending up to about 150 km suggest that the lithosphere may be sufficiently solidified to permit strain accumulation at this depth. Thus the extent of the partial melt may be limited to about 1%.
Highlights
The Andaman Nicobar ridge (ANR) which hosts the Andaman and Nicobar group of islands as well as several sea mounts, is a part of the regional tectonics in the adjoining Bay of Bengal and Andaman sea, resulting from the northward drifting of the Indian plate and its anticlockwise rotation subsequent to the collision with the Eurasian Plate (Curray et al, 1982)
The irregular shape of the crustal block in this region is indicative of the intense tectonic compression that this juvenile crust may have experienced since its formation during the Cretaceous, which has resulted in the eastward thrusting of this crust and the overlying Andaman Flysch at Rangat
The low resistivity feature traced up to depth of about 17 km and beyond beneath this site may be due to the subducting Andaman Flysch
Summary
The Andaman Nicobar ridge (ANR) which hosts the Andaman and Nicobar group of islands as well as several sea mounts, is a part of the regional tectonics in the adjoining Bay of Bengal and Andaman sea, resulting from the northward drifting of the Indian plate and its anticlockwise rotation subsequent to the collision with the Eurasian Plate (Curray et al, 1982). Peter et al (1966) observe from the marine gravity, magnetic and seismic studies that most of the tectonic elements in the Andaman region extend in to the Burmese as well as the Indonesian arcs.
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