Affordable Access

Publisher Website

Gravity field and deep structure of the Bengal Fan and its surrounding continental margins, northeast Indian Ocean

Publication Date
DOI: 10.1016/0040-1951(91)90370-8
  • Geography


Abstract A revised gravity anomaly map for the northeast Indian Ocean shows that the shelf edge underlying the eastern continental margin of India is a rather narrow but extensively linear gravity low (minimum free-air = −149 mGal). The Bengal Fan seaward of the shelf has a depressed gravity field (average free-air = −20 to −30 mGal) in spite of the enormous thickness of sediments of as much as 10–15 km. The two buried ridges below the Bengal Fan—the 85° East and 90° East Ridges—have a large negative (−75 mgal) and a substantial positive (40 mGal) free-air anomaly, respectively. The Andaman and Burmese arcs lying along the east margin of the Bengal Fan are active subduction areas which have typical bipolar gravity signatures with a maximum amplitude of 300 mGal. Gravity interpretation for three regional traverses across the central and northern parts of the Bengal Fan and their surrounding continental margins suggests that a thickened oceanic crustal wedge juxtaposes the transitional crust under the eastern continental slope of India; the 85° East Ridge, that was created when the Indian Ocean lithosphere was very juvenile, appears to underlie a nearly 10 km thick and 120 km wide oceanic crustal block consisting of the ridge material embedded in the upper lithosphere; while the 90° East Ridge submarine topography/buried load below the Bengal Fan is probably isostatically compensated by a low-density mass acting as a cushion at the base of the crust. The Bengal Fan crust, with its thick sediment layer, is carried down the Andaman subduction zone to a depth of about 27 km where, possibly, phase transition takes place under higher pressure. The maximum sediment thickness at the Andaman-Burmese subduction zone is of the order of 10–12 km. The gravity model predicts a low density zone about 60 km wide below the Andaman-Burmese volcanic arc, penetrating from crustal to subcrustal depths in the overriding Burma plate. A more complex density distribution is however, envisaged for the Andaman volcanic arc that is split by the Neogene back arc spreading ridge. The ocean-continent crustal transition possibly occurs farther east of the volcanic arc; below the Shan plateau margin in Burma or below the Mergui terrace at the Malayan continental margin east of the Andaman Sea.

There are no comments yet on this publication. Be the first to share your thoughts.