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A " high 4 He/ 3 He " mantle material detected under the East Pacific Rise (15°4′N)

Abstract : We investigate in details helium isotope data reported in Mougel et al. (2014) for 14 basaltic samples collected on the East Pacific Rise by submersible (15°4′N) where the ridge interacts with the Mathematician seamounts. Samples locations are separated by only few hundred meters across a 15 km along-axis profile. The data reveal a strong geochemical variability that has never been observed at such high spatial resolution for helium isotope compositions. Moreover, they reveal an unusually high 4 He/ 3 He mantle component also characterized by unradiogenic lead, atypical in oceanic basalts. He-Pb systematics suggests a mixture between a nonradiogenic lead and radiogenic helium pyroxenitic component, recycled from the deep continental lithosphere and the ambient peridotitic mantle. The He isotope difference between these two end-members can be interpreted as a time evolution of two distinct mantle sources after a slight (U + Th)/ 3 He fractionation, likely due to some ancient degassing during the formation of deep continental pyroxenites.
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Berengere Mougel, Manuel Moreira, Arnaud Agranier. A " high 4 He/ 3 He " mantle material detected under the East Pacific Rise (15°4′N). Geophysical Research Letters, American Geophysical Union, 2015, 42 (5), pp.1375-1383. ⟨10.1002/2014GL062921⟩. ⟨insu-01141460⟩



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