Structure of the Earth’s Crust and Tectonic Evolution of the Central Bengal Basin

A comprehensive analysis of geological and geophysical data characterizing the structure of the Central Bengal Depression (CBD) and its frame structures was carried out. For the first time, a submeridional deep seismic sounding (DSS) section crossing the CBD is presented. It is found that the consolidated crust in the CBD has a complex block structure. The velocity characteristics of the basement and gradient two-layer structure of the upper mantle unambiguously indicate that the basin formed on continental rather than oceanic crust. The CBD basement subsidence mechanism, the amplitude of which reaches 11 km, may be compaction of mafic rocks of the lower continental crust at its contact with the heated upper mantle and the transition of gabbroid rocks into eclogites with a density of 3.6 g/cm3, which is higher than that of mantle peridotites (3.3 g/cm3). We conclude that the CBD, the 85° E Ridge, and the Bengal sector of the Ninetyeast Ridge are relict fragments of the differentially submerged eastern part of the Indian paleocontinent.