When It Rained Rocks, It Poured Lava

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Science  04 Aug 2000:
Vol. 289, Issue 5480, pp. 697
DOI: 10.1126/science.289.5480.697c

The Deccan flood basalts, one of Earth's largest volcanic provinces, erupted near the time of the Cretaceous-Tertiary boundary and its major extinction (which included the demise of the dinosaurs)—or perhaps was coincident with it. Resolving this question has been difficult because alteration of the Deccan's basalt flows has hindered accurate dating and led to a wide range of age estimates. Hofmann et al. collected samples from the main lava pile and analyzed separate minerals in an attempt to overcome this problem. Dating by 40Ar/39Ar of plagioclase separates from several flows indicates that most of this large pile of lava (2500 meters in thickness) erupted in a relatively short interval (less than 1 million years) about 65.5 million years ago. This age is coincident with dates for the Cretaceous-Tertiary boundary, and the rapid eruption rate is similar to that of most other flood basalt provinces. The authors suggest that previous older ages for these rocks were the result of disturbance of argon in the minerals. — BH

Earth Planet. Sci. Lett. 180, 13 (2000).

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