Validity of the Deccan Chemostratigraphy and Extent of Deccan Formations Beyond the Western Ghats (India)

The Deccan Traps are a continental Large Igneous Province covering large swaths of west-central India, with onshore erupted lava volumes that may have exceeded one million cubic kilometers. The thickest and best exposed sections are in the Western Ghats (WG), a mountainous escarpment that runs roughly parallel to the west coast of India. There, more than 3200 m of near-continuous lava stratigraphy is exposed. Seminal work done in the 1970s and '80s revealed the presence of several regionally traceable geochemical transitions in these sections. Beane et al. (1986, Bulletin of Volcanology v. 48, pp. 61-83), using cluster analysis on a compilation of over 1200 samples, identified stratigraphically and geochemically distinct lava packages in the WG. This chemostratigraphic scheme has served as the foundation for a wide range of Deccan studies, from mapping to understanding the province's architecture, temporal evolution, and feeder system as well as high resolution geochronology. Although the total duration of magmatism is a matter of debate, recent geochronological work done within this chemostratographic framework has demonstrated that the vast majority of volcanism occurred in a short (<1 Ma) interval straddling the Cretaceous-Paleogene boundary. However, the usefulness of the chemostratigraphy has been put into doubt when expanding it beyond the type sections of the WG, and the validity of interpreting units as true chronological markers is unclear. The original statistical analysis focused on elements readily available via X-ray fluorescence. However, issues caused by variable degrees of alteration, fractional crystallization, and crustal assimilation may limit the predictive power of the geochemical clusters as previously defined. Here, we apply machine learning algorithms to Deccan geochemical data to develop a more robust chemostratigraphic Deccan scheme. Such an analysis reveals that the WG lava stratigraphy can be identified over a vast spatial extent of the province, but may not extend to Saurashtra, the Malwa Plateau, or the Mandla Lobe.