R.J. Poreda P.R. Renne F. Teichmann Y.R. Vasiliev N.V. Sobolev B. D. Turrin A. R. Basu 1995 <p><span>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&nbsp;</span>⁴⁰<span>Ar/</span>³⁹<span>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&nbsp;</span>³<span>He/</span>⁴<span>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-</span>³<span>He SFBP plume with a suboceanic-type upper mantle beneath Siberia.</span></p> application/pdf 10.1126/science.269.5225.822 en American Association for the Advancement of Science High-3He plume origin and temporal-spatial evolution of the Siberian flood basalts article