The deep crustal accretion beneath the Laxmi Ridge in the northeastern Arabian Sea: the plume model again

The Laxmi Ridge is the most intriguing structural feature of the northeaste rn Arabian Sea. It is characterized by unusual crustal structure and anomal ous gravity signature. Though the earlier geophysical examinations provide some vital information about its crustal configuration, its origin and evol ution have remained unsolved. Using the available seismic information, the present 2-D together with 3-D gravity modelings of the Laxmi Ridge crust/ma ntle system brought out a transitional layer between the depth of 11-22 km. This anomalous layer is not confined beneath the ridge axis but found to b e present in the entire eastern basin and interpreted as a massive mafic in trusion beneath the region. Thickness of this layer at the base of the crus t beneath the Laxmi Ridge decreases gradually towards the north-west. Howev er, its extension towards the southeast and ultimate connection with the Ch agos-Laccadive Ridge makes the western boundary of the magmatic crustal acc retion along the west coast of India. It is suggested that the Deccan plume head mushrooming beneath the region has modified the crust with a huge mag matic intrusion. The then spreading centre coupled with the Deccan volcanic eruption is held responsible for the present day configuration of the Laxm i Ridge. (C) 1999 Elsevier Science Ltd. All rights reserved.