40Ar/39Ar ages and Sr-Nd-Pb isotopic compositions of alkaline and tholeiitic rocks from the northern Deccan Traps

Abstract:

The Deccan large igneous province in India was emplaced close to the Cretaceous-Paleogene boundary (K-Pg; 66.0 Ma) and is formed by tholeiitic and alkaline rocks. Definition of the origin of Deccan magmatism and of its environmental impact relies on precise and accurate geochronological analyses. We present new ⁴⁰Ar/³⁹Ar ages from the northern sector of the province. In this area, tholeiitic and alkaline rocks were contemporaneously emplaced at 66.60±0.35 to 65.25±0.29 Ma in the Phenai Mata area, while rocks from Rajpipla and Mt. Pavagadh yielded ages ranging from 66.40±2.80 to 64.90±0.80 Ma. Indistinguishable ages for alkaline and tholeiitic magmatism, coupled with distinct major and trace element and Sr-Nd-Pb isotopic compositions suggest that distinct mantle sources, necessary for the two magmatic series were synchronously active.

The new ages are compared with previous ages, which were carefully screened and filtered and then recalculated in order to be comparable. The entire data set of geochronological data does not support a time-related migration of the magmatism related to the northward Indian Plate movement relative to the Reunion mantle plume. The main phase of magmatism, including the newly dated rocks from the Northern Deccan occurred across the K-Pg boundary, confirming a causal link between the emplacement of the province and the K-Pg mass extinction.