EARLY SPREADING AND CONTINENTAL TO OCEANIC BASEMENT TRANSITION BENEATH THE INDUS DEEP-SEA FAN - NORTHEASTERN ARABIAN SEA

A seismic survey to study the Indus deep-sea fan penetrated into basem ent. This enabled the mapping of basement structures and a description of the geodynamical evolution of a part of the northeastern Arabian S ea. The main tectonic structure of the basement is an E-W graben (Gop rift) with a prominent central E-W horst, the Palitana horst. This rif t is cut obliquely by several NE-SW faults. Large E-W magnetic anomali es are not the continuation of the magnetic anomaly sequence of the oc eanic Arabian basin. However, these anomalies are linked to inverse ma gnetisation in the crust, suggesting that the rift is either underlain by stretched continental crust intruded by linear volcanic bodies, re lated to the Deccan Traps, or by oceanic crust older than chron 28 (64 Ma) as proposed in the Laxmi basin southeastwards. Accompanying these structures, NE-SW faults with a strike slip pattern may have played t he role of transform direction during the separation of the Laxmi ridg e from the Indian continent. We propose that rifting and oceanic sprea ding have occurred around a triple junction connecting the oceanic Lax mi basin, the Narmada Son lineament and the Gop rift. This phase prece ded oceanic spreading in the Arabian basin. This interpretation is in agreement with the previously proposed initial separation of India and the Seychelles before chron 28. The Laxmi ridge could be a part of th e Seychelles microplate subsequently left attached to India. (C) 1997 Elsevier Science B.V.