Experimental determination of melt interconnectivity and electrical conductivity in the upper mantle
Experimental determination of melt interconnectivity and electrical conductivity in the upper mantle
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DOI：
10.1016/j.epsl.2017.01.037
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发表时间：
2017-04-01
影响因子：
5.3
通讯作者：
Baumgartner, Lukas P.
中科院分区：
文献类型：
--
作者：
Laumonier, Mickael;Farla, Robert;Baumgartner, Lukas P.
一小部分玄武岩熔体的存在是对在海洋软流圈顶部附近检测到的地幔电导率异常的潜在解释。然而，根据熔体性质和比例对大地电磁剖面的解释依赖于尚未在实际低熔体分数（< 0.01）下进行实验测试的数学模型。为了解决这个问题，我们对部分熔融的橄榄石聚集体进行了原位电导率测量。获得的数据表明，在 1350 摄氏度下，体积电导率遵循传统的阿奇定律，熔体分数指数分别为 0.75 和 1.37，熔体分数大于和小于 0.5 vol.%。我们的结果表明，含熔体橄榄石聚集体中存在多个导电相，连通性阈值类似于熔体的 0.5 vol.%。该模型预测，导电的海洋上层软流圈含有 0.5 至 1 vol.% 的熔体，这与数百万年来，当海洋板块在大洋中脊处分开时，熔体在深处持续存在一致。在洋脊下方，最小渗透率可能允许大洋中脊玄武岩从地幔中升起，我们的模型表明，其中存在的熔体比例高达 4 vol.%。 (C) 2017 Elsevier B.V. 保留所有权利。
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.