Giant Plagioclase Basalts, eruption rate versus time

Abstract

I welcome Sheth’s comments on a more intrigu-ing aspect of my paper, namely, the calculation ofage of the Deccan lava pile in the Western Ghats(type section) using sizes of the “giant” plagioclasecrystals in “Giant Plagioclase Basalt (GPB)” lavaflows. I found the GPB lavas to be very interest-ing because in some cases they clearly mark theboundary between Formations (Hooper et al 1988;Subbarao et al 1988; Khadri et al 1988). They alsoseem to have erupted over bole beds, each of whichpossiblyrepresentsahiatusbetweeneruptiveactiv-ities (Sen 2001). In my view, the latter aspect stillneeds to be proven with solid field work.Sheth correctly points out that typically erup-tion rate is expressed in terms of some sort ofunit volume as a function of time. I did not dothis because I am not sure that we know thevolumes of individual lava flows all that well. Itis clearly something that we need to know bymapping out individual flows in the field. Thatis why I chose to estimate a “one dimensionaleruption rate,” a practice that is not uncommonin experimental and modeling studies. I was ini-tially encouraged by Sheth’s new (and correct)eruption rate calculations based on my approach,suggesting that the Western Ghats section spana time of 4.4m.y. He notes that this range coin-cides very well with the