Deccan Traps

Abstract

The Indian subcontinent is blanketed with the remnants of at least five continental flood basalt provinces ranging in age from the Middle Proterozoic to the Late Cretaceous-Early Tertiary. Not surprisingly, the youngest of these, the Deccan plateau (derived from a Sanskrit word meaning “south” or “southern”) is by far the best-preserved and most extensive, presently occupying some half a million square kilometers of western and central India and southernmost Pakistan (Fig. 1). Until quite recently comparatively little was known about the geology of the body of this vast province, save that it was comprised of thick successsions of nearly flat-lying, subaerially erupted, predominantly tholeiitic lava flows, at least some of which were traceable for distances of more than 100 km. Neither the gross features nor the details of flow stratigraphy, eruptive source locations, regional structure, or chemical and isotopic variations were understood; ages and age distributions were imperfectly known, and ideas on mantle sources and petrogenesis remained largely in the realm of speculation. Up to and throughout the 1970’s it was not unusual to see arguments in the literature that relied heavily on pioneering studies done in the 1800’s or early years of this century. A voluminous amount of work did exist on the scattered, small alkalic and acidic intrusive suites dotting the western and northern areas of the Deccan. Although lithologically distinctive in a sea of tholeiitic lava, they are volumetrically insignificant and for the most part appear to post-date the main phase of eruptive activity. Studies of these restricted occurrences therefore were unable to shed much light on the fundamental nature of the plateau itself. Only in the last several years have detailed, systematic investigations been conducted on a regional scale, utilizing a combination of modern methods.