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Science. 2019 Aug 16;365(6454):692-694. doi: 10.1126/science.aax5293.

Primordial and recycled helium isotope signatures in the mantle transition zone.

Author information

1
Research School of Earth Sciences, Australian National University, 142 Mills Road, Acton, ACT 2601, Australia. suzette.timmerman@anu.edu.au.
2
Research School of Earth Sciences, Australian National University, 142 Mills Road, Acton, ACT 2601, Australia.
3
Earth and Atmospheric Sciences, University of Alberta, 116 Street and 85 Avenue, Edmonton, Alberta T6G 2R3, Canada.
4
School of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1QU, UK.
5
School of Geographical and Earth Sciences, Gregory Building, University of Glasgow, Glasgow G12 8QQ, UK.
6
University of Sao Paolo, Sao Paolo, Brazil.

Abstract

Isotope compositions of basalts provide information about the chemical reservoirs in Earth's interior and play a critical role in defining models of Earth's structure. However, the helium isotope signature of the mantle below depths of a few hundred kilometers has been difficult to measure directly. This information is a vital baseline for understanding helium isotopes in erupted basalts. We measured He-Sr-Pb isotope ratios in superdeep diamond fluid inclusions from the transition zone (depth of 410 to 660 kilometers) unaffected by degassing and shallow crustal contamination. We found extreme He-C-Pb-Sr isotope variability, with high 3He/4He ratios related to higher helium concentrations. This indicates that a less degassed, high-3He/4He deep mantle source infiltrates the transition zone, where it interacts with recycled material, creating the diverse compositions recorded in ocean island basalts.

PMID:
31416962
DOI:
10.1126/science.aax5293

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