40Ar-39Ar age of a lava flow from the Bhimashankar Formation, Giravali Ghat, Deccan Traps

Abstract

We report here a 40 Ar-39 Ar age of 66.0 ± 0.9 Ma (2σ) for a reversely magnetised tholeiitic lava flow from the Bhimashankar Formation (Fm.), Giravali Ghat, western Deccan province, India. This age is consistent with the view that the 1.8-2 km thick bottom part of the exposed basalt flow sequence in the Western Ghats was extruded very close to 67.4 Ma.

Triggering of the largest Deccan eruptions by the Chicxulub impact

“…Ar plateau ages for lavas in the Western Ghats that are assigned to specifi c formations, published since the year 1990, along with 2σ error bars (Venkatesan et al, 1993;Hofmann et al, 2000;Knight et al, 2003;Pande et al, 2004;Hooper et al, 2010). All ages have been recalculated per the calibration of Renne et al (2011).…”

The emplacement of pahoehoe lavas on Kilauea and in the Deccan Traps

“…eruptive duration for the thick Western Ghats sequence (e.g., Hofmann et al 2000) and others for a 4-5 m.y. duration (e.g., Venkatesan et al 1993;Pande 2002;Pande et al 2004), with Sheth et al (2001a, b) reporting that the total duration of the volcanism, including late-stage basalts and felsic volcanics, was at least 8-9 m.y. Until this issue gets resolved it is not possible to directly calculate a bulk volumetric eruption rate for the Western Ghats lava pile, much less the entire province.…”

“…Fresh glass is hard to find in the Deccan basalts, owing to widespread alteration through 65 m.y., but measurements on melt inclusions in any unaltered phenocrysts will help to unambiguously establish the pre-degassing magmatic volatile contents of the Deccan magmas, and how much may have been released into the atmosphere by them. Venkatesan et al (1993) and more recently Pande (2002) and Pande et al (2004) have been arguing that the lower part (notably dominated by the compound pahoehoe flows) of the 3-km-thick Western Ghats lava pile significantly preceded the K-T extinctions. If so, this would be consistent with the morphology and emplacement mechanisms of the lavas.…”

Untitled

“…These lavas reach a maximum thickness of 2.7 kilometers at the Western Ghats of India. Argon ( 40 Ar/ 39 Ar) studies from different laboratories reach different conclusions about the timing of this eruption: 65 ± 0.9 million years ago (Ma) [e.g., Hofmann et al, 2000] versus 66-67.4 ± 0.9 Ma [Pande et al, 2004].…”