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

1995; American Association for the Advancement of Science; Volume: 269; Issue: 5225 Linguagem: Inglês

10.1126/science.269.5225.822

1095-9203

Asish R. Basu, Robert J. Poreda, Paul R. Renne, Friedrich Teichmann, Yu. R. Vasiliev, N. V. Sobolev, B. D. Turrin,

High-pressure geophysics and materials

An olivine nephelinite from the lower part of a thick alkalic ultrabasic and mafic sequence of volcanic rocks of the northeastern part of the Siberian flood basalt province (SFBP) yielded a (40)Ar/(39)Ar plateau age of 253.3 +/- 2.6 million years, distinctly older than the main tholeiitic pulse of the SFBP at 250.0 million years. Olivine phenocrysts of this rock showed (3)He/(4)He ratios up to 12.7 times the atmospheric ratio; these values suggest a lower mantle plume origin. The neodymium and strontium isotopes, rare earth element concentration patterns, and cerium/lead ratios of the associated rocks were also consistent with their derivation from a near-chondritic, primitive plume. Geochemical data from the 250-million-year-old volcanic rocks higher up in the sequence indicate interaction of this high-(3)He SFBP plume with a suboceanic-type upper mantle beneath Siberia.