'A'(a)over-bar lava flows in the Deccan Volcanic Province, India, and their significance for the nature of continental flood basalt eruptions

Newly identified 'A'(a) over bar lava flows outcrop intermittently over an area of similar to 110 km(2) in the western Deccan Volcanic Province (DVP), India. They occur in the upper Thakurvadi Formation in the region south of Sangamner. The flows, one of which is compound, are 15-25 m thick, and exhibit well-developed basal and flow-top breccias. The lavas have microcrystalline groundmasses and are porphyritic or glomerocrystic and contain phenocrysts of olivine, clinopyroxene or plagioclase feldspar. They are chemically similar to compound pAhoehoe flows at a similar stratigraphic horizon along the Western Ghats. Petrographic and geochemical differences between 'A'(a) over bar flows at widely spaced outcrops at the same stratigraphic horizon suggest that they are the product of several eruptions, potentially from different sources. Their presence in the DVP could suggest relative proximity to vents. This discovery is significant because 'A'(a) over bar lavas are generally scarce in large continental flood basalt provinces, which typically consist of numerous inflated compound pAhoehoe lobes and sheet lobes. Their scarcity is intriguing, and may relate to either their occurrence only in poorly preserved or exposed proximal areas or to the flat plateau-like topography of flood basalt provinces that may inhibit channelization and 'A'(a) over bar formation, or both. In this context, the 'A'(a) over bar flow fields described here are inferred to be the products of eruptions that produced unusually high-effusion-rate lavas compared to typical flood basalt eruptions. Whether these phases were transitional to lower intensity, sustained eruptions that fed extensive low effusion rate pAhoehoe flow fields remains unclear.