The relationship between rifting and magmatism in the northeastern Arabian Sea

摘要

The causal mechanisms linking continental flood basalts, lithospheric extension and mantle plumes, as well as the relative timing of extension and volcanism, are controversial(1-4). The eruption of the Deccan flood basalts was approximately contemporaneous with the separation of the Seychelles microcontinent from India. However, between these continental blocks lies the enigmatic Laxmi Ridge, and the sequence of extensional events that formed these various tectonic elements is poorly understood. Here we present wide-angle seismic data along a profile across Laxmi Ridge that permit delineation of offshore igneous bodies associated with the Deccan magmatism; these bodies are similar to those associated with flood-basalt volcanism and rifting in the Atlantic region and elsewhere(1). From the geometry of these bodies, we infer that there were two periods of extension. The first phase, which involved extension between Laxmi Ridge and the Indian subcontinent, was accompanied by significant Deccan-related magmatism. Full development of a continental margin was achieved during the second phase of weakly magmatic extension between Laxmi Ridge and the Seychelles. We suggest that between these rifting events the region passed beyond the reach of lateral flow from the source region of the Deccan flood basalts.