Record Details
Helium isotopic textures in Earth’s upper mantle
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Helium isotopic textures in Earth’s upper mantle |
| Names |
Graham, David W.
(creator) Hanan, Barry B. (creator) Hémond, Christophe (creator) Blichert-Toft, Janne (creator) Albaréde, Francis (creator) |
| Date Issued | 2014-05-30 (iso8601) |
| Note | This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291525-2027. |
| Abstract | We report ³He/⁴He for 150 mid-ocean ridge basalt (MORB) glasses from the Southeast Indian Ridge (SEIR). Between 81°E and 101°E ³He/⁴He varies from 7.5 to 10.2 R[subscript A], encompassing more than half the MORB range away from ocean island hot spots. Abrupt transitions are present and in one case the full range occurs over ~10 km. Melting of lithologically heterogeneous mantle containing a few percent garnet pyroxenite or eclogite leads to lower ³He/⁴He, while ³He/⁴He above ~9 R[subscript A] likely indicates melting of pyroxenite-free or eclogite-free mantle. Patterns in the length scales of variability represent a description of helium isotopic texture. We utilize four complementary methods of spectral analysis to evaluate this texture, including periodogram, redfit, multitaper method, and continuous wavelet transform. Long-wavelength lobes with prominent power at 1000 and 500 km are present in all treatments, similar to hot spot-type spectra in Atlantic periodograms. The densely sampled region of the SEIR considered separately shows significant power at ~100 and ~30–40 km, the latter scale resembling heterogeneity in the bimodal distribution of Hf and Pb isotopes in the same sample suite. Wavelet transform coherence reveals that ³He/⁴He varies in-phase with axial depth along the SEIR at ~1000 km length scale, suggesting a coupling between melt production, ³He/⁴He and regional variations in mantle temperature. Collectively, our results show that the length scales of MORB ³He/⁴He variability are dominantly controlled by folding and stretching of heterogeneities during regional (~1000 km) and mesoscale (~100 km) mantle flow, and by sampling during the partial melting process (~30 km). |
| Genre | Article |
| Topic | Helium isotopes |
| Identifier | Graham, D. W., B. B. Hanan, C. Hémond, J. Blichert-Toft, and F. Albarède (2014), Helium isotopic textures in Earth's upper mantle. Geochemistry Geophysics Geosystems, 15, 2048–2074. doi:10.1002/2014GC005264 |
