Variability in the crustal structure of the West Indian Continental Margin in the Northern Arabian Sea

Abstract

ABSTRACT In this case study of the West Indian Continental Margin we present an interpretation of a volcanic margin structure based on regional mapping of high quality 2D seismic data in conjunction with regional satellite derived gravity data and selected subsidence analyses. The area shows many classic characteristics of a volcanic-type margin. Volcanic facies identified and mapped along the margin include seaward-dipping reflectors (SDRs), sub-aerial seamounts, clinoform packages interpreted as lava and volcaniclastic delta systems and thick, seismically layered sequences interpreted as volcanically derived sediment deposited in both fluvial and marine environments. The results show major variation in the overall thickness and style of volcanism across the margin both in dip and strike directions which may be related to variability in influence of the Deccan Plume in addition to localization along structural features inherited from older tectonic events. Our interpretation of rapid lateral variation in the thickness of extrusive volcanism has important implications for the distribution, preservation and hydrocarbon potential of the pre-rift sequence across the margin. The interpreted crustal structure also has a major impact on predictions of the historical and present-day heat-flow into the post-rift section. Our interpretation of the timing and distribution of volcanism is consistent with the presence of a broad region of elevated mantle potential temperatures at the time of the final break-up event on the West Indian Continental Margin, commonly attributed to the Deccan/Reunion Plume. Pre-existing structural heterogeneities appear to have played an important part in controlling the distribution of volcanism. Interpreted tectonic subsidence, based on backstripping analysis of the post-break-up interval, is also shown to be consistent with post-break-up thermal subsidence in combination with dynamic support associated with the elevated mantle temperatures into the Early Eocene.