Pulsating dynamics of thermal plumes and its implications for multiple eruption events in the Deccan Traps, India

Abstract

In Earth's mantle gravity instabilities initiated by density inversion lead to upwelling of hot materials as plumes. This study focuses upon the problem of their ascent dynamics to provide an explanation of the periodic multiple eruption events in large igneous provinces and hotspots. We demonstrate from physical experiments that plumes can ascend in a continuous process to form a single large head trailing into a long slender tail, typically described in the literature only under specific physical conditions. Alternatively, they ascend in a pulsating fashion, and produce multiple in-axis heads of varying dimensions. Based on the Volume of Fluid (VOF) method, we performed computational fluid dynamics (CFD) simulations to constrain the thermo-mechanical conditions that decide the continuous versus pulsating dynamics. Our CFD simulations suggest the density ($\rho^*$) and the viscosity ($R$) ratios of the ambient to the plume materials and the influx rates ($Re$) are the prime factors in controlling the ascent dynamics. Conditions with large $R$ ($>$50) develop pulsating plumes, which are sustained preferentially under low $\rho^*$ and $Re$ conditions. Again, the increasing temperature difference between the plume and the ambient medium is found to promote pulsating behaviour. From these CFD simulations we show the thermal structures of a plume, and predict the peak thermal events near the surface that commence periodically as pulses with a time interval of 1.4-3 Ma. The pulsating plume model explains the multiple eruption events in the Deccan Traps in India, where the time scale of their intervals estimated from the available $^{40}Ar$/$^{39}Ar$ geochronological data shows an excellent match with our simulation results.