Sr, Nd and Pb isotopic and chemical compositions of central Deccan Traps lavas and relation to southwestern Deccan stratigraphy

Abstract Sr, Nd and Pb isotopic compositions, and major and trace element abundances of lavas in five central Deccan Traps sections are generally very similar to those of lavas in the southwestern Deccan (Western Ghats escarpment). The combination of strong isotopic and chemical similarities between lavas of the two regions indicates that they shared a closely similar petrogenesis. Our results indicate that, unlike many lavas in the northeastern Deccan, most of the lavas studied in the central Deccan sections can be grouped into different stratigraphic members and chemical types (CTs) belonging to four formations (Thakurvadi, Bhimashankar, Khandala, and Poladpur) present in the type sections of the Western Ghats. Bhimashankar- and Thakurvadi-type lavas are found in a section near Outram, whereas only Khandala-type lavas make up the Mhaishmal, Ellora and Ajanta sections to the east, and only Poladpur-type lavas are present in the easternmost section at Lonar. This west-east sequence is the same as that seen going upward in the Western Ghats stratigraphy, except that Bushe-type lavas, which are located stratigraphically between the Khandala and Poladpur formations in the Western Ghats, have not been found in this study. Overall, our results indicate that the Khandala and Poladpur formations extend over west-east distances of more than 300 km, and some individual members (e.g., the Dhak Dongar) may extend over as much as 500 km. The regional dip from Igatpuri in the southwest to Lonar in the east-central Deccan is less than 0.5° to the east, which is similar to the southward regional dip in the southwestern Deccan. Near-horizontal flows in the central and southwestern Deccan areas suggest that post-Deccan tectonic activity has had limited effects on the studied area. Large volumes of basaltic lavas derived from eruptive centers in the western Deccan may have covered both the central and southwestern Deccan areas.