Electrical conductivity of basaltic and carbonatite melt-bearing peridotites at high pressures: Implications for melt distribution and melt fraction in the upper mantle
Electrical conductivity of basaltic and carbonatite melt-bearing peridotites at high pressures: Implications for melt distribution and melt fraction in the upper mantle
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DOI：
10.1016/j.epsl.2010.04.050
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发表时间：
2010-07
影响因子：
5.3
通讯作者：
T. Yoshino;M. Laumonier;E. Mcisaac;T. Katsura
中科院分区：
文献类型：
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作者：
T. Yoshino;M. Laumonier;E. Mcisaac;T. Katsura
为了研究高压下部分熔融地幔橄榄岩的熔体分数-电导率关系和熔体分布，在Kawai型多砧装置上对玄武岩和碳酸岩两种部分熔融样品进行了电阻抗测量。硅酸盐样品由San卡洛斯橄榄石和不同量的洋中脊玄武岩（MORB）组成，碳酸盐样品由San卡洛斯橄榄石和不同量的碳酸盐岩组成。对硅酸盐和碳酸盐体系进行了高压实验，分别在1.5GPa下达到1600 K和3GPa下达到至少1650 K。样品电导率随着熔体分数的增加而增加。含碳酸盐岩样品的电导率比含玄武岩样品的电导率高出一个数量级。电导率对数（σbulk）与熔体分数对数（σ melt）之间的线性关系可用阿尔奇定律（Archie，1942）（σbulk/σmelt= Cn）来描述，其参数C分别为0.68和0.97，n分别为0.87和1.13。熔体分布的理论预测的电导率数据的比较表明，该模型假设晶界完全润湿熔体是最优选的熔体几何形状。电导率随熔体分数的逐渐变化表明，在一定的熔体分数下，由于熔体渗流，没有渗透率跳跃。上地幔部分熔融区的玄武岩熔体和碳酸岩熔体的熔融分数分别为1-3%和1.00%。
Electrical impedance measurements were performed on two types of partial molten samples with basaltic and carbonatitic melts in a Kawai-type multi-anvil apparatus in order to investigate melt fraction–conductivity relationships and melt distribution of the partial molten mantle peridotite under high pressure. The silicate samples were composed of San Carlos olivine with various amounts of mid-ocean ridge basalt (MORB), and the carbonate samples were a mixture of San Carlos olivine with various amounts of carbonatite. High-pressure experiments on the silicate and carbonate systems were performed up to 1600K at 1.5GPa and up to at least 1650K at 3GPa, respectively. The sample conductivity increased with increasing melt fraction. Carbonatite-bearing samples show approximately one order of magnitude higher conductivity than basalt-bearing ones at the similar melt fraction. A linear relationship between log conductivity (σbulk) and log melt fraction (ϕ) can be expressed well by the Archie's law (Archie, 1942) (σbulk/σmelt=Cϕn) with parameters C=0.68 and 0.97, n=0.87 and 1.13 for silicate and carbonate systems, respectively. Comparison of the electrical conductivity data with theoretical predictions for melt distribution indicates that the model assuming that the grain boundary is completely wetted by melt is the most preferable melt geometry. The gradual change of conductivity with melt fraction suggests no permeability jump due to melt percolation at a certain melt fraction. The melt fraction of the partial molten region in the upper mantle can be estimated to be 1–3% and ∼0.3% for basaltic melt and carbonatite melt, respectively.