Emplacement of amba dongar carbonatite-alkaline complex at Cretaceous/Tertiary boundary: Evidence from Ar-40-Ar-39 chronology

Ar-40-Ar-39 analyses of three fresh alkaline rock samples and a phlogopite separate from a carbonatite from Amba Dongar carbonatite-alkaline complex o f the Deccan Flood Basalt Province, India, yield indistinguishable precise plateau ages of 64.8+/-0.6, 64.7+/-0.5, 65.5+/-0.8 and 65.3+/-0.6 Ma, givin g a mean plateau age of 65.0+/-0.3 Ma, which is the age of emplacement of t his complex. This age implies contemporaneity of Amba Dongar with several o ther carbonatite-alkaline activities of Chhota Udaipur subprovince and is c onsistent with their Reunion-Deccan plume origin hypothesis. The emplacemen t of these complexes at 65 Ma makes them very significant in the ongoing de bate on the K/T extinctions owing to their capacity to rapidly inject a sub stantial amount of CO2 and SO2 into the atmosphere.