The timing of crustal extension and the eruption of continental flood basalts

Abstract

THE association between mantle plumes, continental flood basalt eruption and the extension and rifting of the crust is well recognized1–3, but there has always been controversy as to whether the plume or the rifting was the initiating factor4,5. Was rifting triggered by doming above the thermal plume2,3,6, or was rifting the driving force, preceding the associated volcanicity7,8? Here I show that recent flow-by-flow mapping of two continental flood basalt provinces, the Columbia River Basalt Group and the Deccan Basalt Group, allows one to infer the relative timing of volcanicity and crustal extension. In both provinces, eruption of the main tholeiitic phase preceded significant extension and crustal thinning. This suggests that the primary event in the formation of these provinces was the upwelling of a mantle plume, and that the subsequent crustal extension, rifting and decompression was in part a consequence of the initiation of that plume.