Australia: The Land Where Time Began

A biography of the Australian continent 

Siberian Flood Basalts - High ³He Plume Origin and Temporal Spatial Evolution

In this study the authors¹ obtained an ⁴⁰Ar/³⁹Ar plateau age of 253.3 ± 2.6 Ma from an olivine nephelinite that had been obtained from the lower part of a thick alkalic ultrabasic and mafic sequence of volcanic rocks from the northeastern section of the Siberian Flood Basalt Province (SFBP), that is older than the 250 Ma date of the main tholeiitic pulse of the SFBP. The authors¹ found ³He/⁴He ratios of up to 12.7 times the ratio present in the atmosphere when they analysed olivine phenocrysts of these rocks, which suggested a lower mantle plume origin. Other features of the associated rocks that were consistent with the rocks being derived from a primitive plume that was near-chondritic were the neodymium and strontium isotopes, concentration patterns of rare earth elements, and cerium/lead ratios. Interaction of this high ³He SFBP plume with a sub-oceanic type upper mantle beneath Siberia is indicated by geochemical data from volcanic rocks, that date to 250 Ma, that were higher up in the sequence.

Sources & Further reading

1. Basu, Asish R., Robert J. Poreda, Paul R. Renne, Friedrich Teichmann, Yurii R. Vasiliev, Nikolai V. Sobolev, and Brent D. Turrin. "High-3he Plume Origin and Temporal-Spatial Evolution of the Siberian Flood Basalts." Science 269, no. 5225 (August 11, 1995 1995): 822-25.