title: Early and Late Alkali Igneous Pulses and a High-3He Plume Origin for the Deccan Flood Basalts.
abstract: Several alkalic igneous complexes of nephelinite-carbonatite affinities occur in extensional zones around a region of high heat flow and positive gravity anomaly within the continental flood basalt (CFB) province of Deccan, India. Biotites from two of the complexes yield (40)Ar/(39)Ar dates of 68.53 +/- 0.16 and 68.57 +/- 0.08 million years. Biotite from a third complex, which intrudes the flood basalts, yields an (40)Ar/(39)Ar date of 64.96 +/- 0.1 1 million years. The complexes thus represent early and late magmatism with respect to the main pulse of CFB volcanism 65 million years ago. Rocks from the older complexes show a (3)He/(4)He ratio of 14.0 times the air ratio, an initial (87)Sr/(86)Sr ratio of 0.70483, and other geochemical characteristics similar to ocean island basalts; the later alkalic pulse shows isotopic evidence of crustal contamination. The data document 3.5 million years of incubation of a primitive, high-(3)He mantle plume before the rapid eruption of the Deccan CFB.
authors.forename: A R
authors.initials: AR
authors.lastname: Basu
authors.forename: P R
authors.initials: PR
authors.lastname: Renne
authors.forename: D K
authors.initials: DK
authors.lastname: Dasgupta
authors.forename: F
authors.initials: F
authors.lastname: Teichmann
authors.forename: R J
authors.initials: RJ
authors.lastname: Poreda