Highest terrestrial 3He/4He credibly from the core.
F Horton1, P D Asimow2, K A Farley2
1Geology and Geophysics Department, Woods Hole Oceanographic Institution, Woods Hole, MA, USA. fhorton@whoi.edu.
Nature
|October 18, 2023
Summary
Scientists discovered exceptionally high helium-3 (³He) to helium-4 (⁴He) ratios in Baffin Island lavas, suggesting a potential core origin for this primordial gas. This finding challenges the long-held view of helium
Area of Science:
- Geochemistry
- Geophysics
- Earth Science
Background:
- Mantle plume lavas typically exhibit higher ³He/⁴He ratios than the upper mantle.
- High ³He/⁴He ratios are traditionally attributed to primordial material from the solar nebula incorporated during Earth's accretion.
- This component was thought to have remained isolated in the mantle, avoiding outgassing events.
Purpose of the Study:
- To investigate the origin of exceptionally high ³He/⁴He ratios in terrestrial igneous rocks.
- To test the hypothesis that Earth's core could be a source of primordial helium.
- To re-evaluate models of volatile element evolution in Earth's deep interior.
Main Methods:
- Analysis of helium isotope ratios (³He/⁴He) in olivine crystals from Baffin Island lavas.
- Geochemical and geophysical modeling to assess potential helium sources.
Main Results:
- The highest magmatic ³He/⁴He ratio ever recorded in terrestrial igneous rocks was measured (67.2 ± 1.8 times the atmospheric ratio).
- The observed ratios in Baffin Island lavas are consistent with a potential contribution from Earth's core.
- This finding challenges the established understanding of primordial helium's location and survival within the Earth.
Conclusions:
- The Earth's core may be a viable source for the high ³He/⁴He observed in some mantle plume lavas.
- The presence of such high ratios challenges the long-standing assumption that primordial volatiles have exclusively survived in the mantle.
- This discovery necessitates a revision of models concerning the deep Earth's volatile inventory and its evolution.
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