Magnetostratigraphy and 40Ar–39Ar geochronology of the Malwa Plateau region (Northern Deccan Traps), central western India: Significance and correlation with the main Deccan Large Igneous Province sequences

Abstract

Basaltic lava flows of Malwa Plateau together with the Mandla area and the Toranmal section constitute the Northern Deccan Province in central western India. With the present outcrop area of 80,000km2 the Malwa flows form an extensive but relatively thin sequence.We sampled Deccan basalts along two 100km each N–S and E–W transects along the western and southern rims of the Malwa Plateau. The 67.12±0.44Ma 40Ar–39Ar age obtained in the present study clearly shows that the eruption of the Malwa flows started during the magnetochron C30n. By mapping the magnetic C30n/C29r transition on the western and southern edge of the plateau, the total volume and eruption rate can be calculated (42,000km3; 0.03km3/a). Furthermore the results point towards the Narmada-Tapi rift zone as the possible source area for the Malwa lava flows.The Malwa sequence is older and partly synchronous with the thick sequences of the Western Ghats. Since their eruption centers are spatially independent, they should not be correlated with younger, although geochemically similar, formations of the Western Ghats. Other Northern Deccan flows show clear similarities with the Malwa flows and can be magnetostratigraphically and geochemically correlated. We therefore suggest a new subgroup for the Northern Deccan Province, the “Narmada Subgroup”, defined on the geochemical and magnetic characteristics of the Malwa, Mandla and Toranmal flows. The introduction of this new subgroup clarifies the position of the Northern Deccan Province in the Deccan stratigraphy and is a step towards a better understanding of the Deccan eruption history.