Geology and Geochemistry of the Sangamner Mafic Dike Swarm, Western Deccan Volcanic Province, India: Implications for Regional Stratigraphy

Numerous large, NE‐SW‐ to E‐W‐trending mafic dikes outcrop around Sangamner in the western Deccan Volcanic Province. This area is part of a broader region postulated to be a shieldlike feature and a major eruption center. A combination of field, geochemical, and isotopic (Sr and Nd) characteristics is used here to understand the relationship of this dike swarm with the associated lava flows and their position in the established Deccan stratigraphy. Many dikes are compositionally similar to the Khandala and Poladpur formations belonging to the Lonavala and Wai subgroups, respectively, while one dike is similar to the Ambenali Formation. One dike has a composition distinct from all other dikes in this area as well as from most stratigraphic units, although there are many similarities in composition with the Bushe Formation as well as the Boyhare Member of the Khandala Formation. While several dikes are geochemically similar to specific flows/members within certain formations, their isotopic composition is often different, sometimes significantly so. This implies either that there is a greater range in isotopic composition for those members than previously realized or that magmas with different isotopic compositions underwent broadly similar petrogenetic evolution leading to similarities in elemental composition. NE‐SW‐trending Poladpur‐ and/or Khandala‐like dikes are concentrated in the central part of the area; these dikes appear to represent a vent system that could have fed southern, western, or eastern exposures of these younger formations. It is also possible, however, that some or many of the dikes along this system were simply late‐stage intrusions of magmas representing the younger formations.