Australia: The Land Where Time Began

A biography of the Australian continent 

Deccan Flood Basalts - Early and Late Igneous Pulses and a High ³He Plume Origin

According to Basu et al. a number of alkalic complexes have been found, that have nephelinite-carbonatite affinities, in extensional zones around a region that has high heat flow and a positive gravity anomaly within the Continental Flood Basalt (CFB) province of Deccan, India. ⁴⁰Ar,³⁹Ar dates were found for samples of biotite from 2 of the complexes of 68.53 ± 0.16 Ma and 68.27 ± 0.08 Ma. Biotite samples from a third site, intruding into the flood basalt, had an ⁴⁰Ar/³⁹Ar date of 64.96 ± 0.11 Ma. Therefore the dates from the complexes indicate that the complexes represent early and late magmatism with respect to the main volcanism pulse of the CFB that occurred 65 Ma. A ³He/⁴He ratio of 14.0 times the ratio in the atmosphere was found in the older complexes, an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.70483, as well as other geochemical characteristics that are similar to those found in ocean island basalts, while the later alkalic pulse shows isotopic evidence of crustal contamination. It is documented by the data that primitive high-³He mantle plume was incubated for 3.5 Ma prior to the rapid eruption of the Deccan CFB.

Sources & Further reading

1. Basu, Asish R., Paul R. Renne, Deb K. DasGupta, Friedrich Teichmann, and Robert J. Poreda. "Early and Late Alkali Igneous Pulses and a High-3he Plume Origin for the Deccan Flood Basalts." Science 261, no. 5123 (August 13, 1993 1993): 902-06.