期刊
EARTH AND PLANETARY SCIENCE LETTERS
卷 463, 期 -, 页码 286-297出版社
ELSEVIER
DOI: 10.1016/j.epsl.2017.01.037
关键词
electrical conductivity; upper mantle; Low Velocity Zone; melt interconnectivity; olivine aggregate; basalt
资金
- Alexander von Humboldt Foundation
- free state of Bavaria
- German Research Foundation (DFG) [MA 6278/2-1, MA 6278/3-1]
The presence of a small fraction of basaltic melt is a potential explanation for mantle electrical conductivity anomalies detected near the top of the oceanic asthenosphere. The interpretation of magnetotelluric profiles in terms of the nature and proportion of melt, however, relies on mathematical models that have not been experimentally tested at realistically low melt fractions (< 0.01). In order to address this, we have performed in situelectrical conductivity measurements on partially molten olivine aggregates. The obtained data suggest that the bulk conductivity follows the conventional Archie's law with the melt fraction exponents of 0.75 and 1.37 at melt fractions greater and smaller than 0.5 vol.% respectively at 1350 degrees C. Our results imply multiple conducting phases in melt- bearing olivine aggregate and a connectedness threshold at similar to 0.5 vol.% of melt. The model predicts that the conductive oceanic upper asthenosphere contains 0.5 to 1 vol.% of melt, which is consistent with the durable presence of melt at depths over millions years while the oceanic plates spread apart at the mid- ocean ridge. Beneath ridges a minimum permeability may allow mid- ocean ridge basalts to rise out of the mantle, where our model indicates that melt is present in proportions of up to 4 vol.%. (C) 2017 Elsevier B. V. All rights reserved.
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