New palaeomagnetic data from the Mahabaleshwar Plateau, Deccan Flood Basalt Province, India: implications for the volcanostratigraphic architecture of continental flood basalt provinces

Abstract

New magnetostratigraphic data from seven Western Ghats sections in the Deccan Volcanic Province are presented. These are combined with an established geochemically defined stratigraphy, and volcanological logs, to provide a correlated, chronological eruptive framework. We identify two magnetic polarities in five of the sections, and these are assigned to chrons 29r and 29n. Importantly, the reversal boundary represents an identifiable isochronous surface within the volcanic pile. This surface occurs at different elevations, as does the altitude of the geochemically defined formation boundary (i.e. Ambenali–Mahabaleshwar Fms), which defines a second isochronous surface. Inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces. This indicates that there was significant local topography ( c . 80 m) across Deccan Volcanic Province lava fields during their development; an interpretation consistent with topographies observed across modern and historical examples (e.g. Hawaii, Iceland). These data also indicate that the geochemical stratigraphies of continental flood basalt provinces can mask local and sub-regional detail in lava stacking patterns when applied at smaller spatial scales (<10 2 –10 4 m). Finally, transitional (R–N) directions preserved in some eruptive units place constraints upon the rates of eruption, and indicate c . 2 ka periods of volcanic repose.