Helium isotopic textures in Earth's upper mantle
| Type | Article | ||||||||
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| Date | 2014-05 | ||||||||
| Language | English | ||||||||
| Author(s) | Graham David W.1, Hanan Barry B.2, Hemond Christophe3, Blichert-Toft Janne4, 5, Albarede Francis4, 5 | ||||||||
| Affiliation(s) | 1 : Oregon State Univ, Coll Earth Ocean & Atmospher Sci, Corvallis, OR 97331 USA. 2 : San Diego State Univ, Dept Geol Sci, San Diego, CA 92182 USA. 3 : Inst Univ Europeen Mer, Plouzane, France. 4 : Ecole Normale Super Lyon, Lab Geol Lyon, F-69364 Lyon, France. 5 : Univ Lyon 1, CNRS, UMR 5276, F-69365 Lyon, France. |
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| Source | Geochemistry Geophysics Geosystems (1525-2027) (Amer Geophysical Union), 2014-05 , Vol. 15 , N. 5 , P. 2048-2074 | ||||||||
| DOI | 10.1002/2014GC005264 | ||||||||
| WOS© Times Cited | 38 | ||||||||
| Abstract | We report He-3/He-4 for 150 mid-ocean ridge basalt (MORB) glasses from the Southeast Indian Ridge (SEIR). Between 81 degrees E and 101 degrees E He-3/He-4 varies from 7.5 to 10.2 R-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 similar to 10 km. Melting of lithologically heterogeneous mantle containing a few percent garnet pyroxenite or eclogite leads to lower He-3/He-4, while He-3/He-4 above similar to 9 R-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 similar to 100 and similar to 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 He-3/He-4 varies in-phase with axial depth along the SEIR at similar to 1000 km length scale, suggesting a coupling between melt production, He-3/He-4 and regional variations in mantle temperature. Collectively, our results show that the length scales of MORB He-3/He-4 variability are dominantly controlled by folding and stretching of heterogeneities during regional (similar to 1000 km) and mesoscale (similar to 100 km) mantle flow, and by sampling during the partial melting process (similar to 30 km). | ||||||||
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