Partial melt below Iceland: A combined interpretation of seismic and conductivity data

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Abstract
A combined interpretation of published seismic and electric data is carried out to impose constraints on the state of melting below Central Iceland. These data indicate high electrical conductivity and low vp velocity (regionally below 6 km/s) for the crust‐mantle transition region, while the mantle below shows lower conductivity but still anomalous low velocity. The velocity data are treated by utilizing gravity data to quantify the elastic modulus decrease due to partial melt. A comprehensive set of theoretical models on elasticity, anelasticity, and electrical conductivity of partially molten rock is applied to this data set. The geometry, the fraction, and the interconnection of the melt phase are varied systematically. The conductivity models are based on published laboratory data on conductivity of solid and melt phases of rocks. Anisotropy and possible unexplored conductivity mechanisms near the melting temperature are not considered here. By means of the melt models the data can be explained most easily as follows: in a depth range roughly between 20 and 50 km only a small percentage of melt (≦2%, at the most 5% if melt pockets are also present) occurs in thin films, possibly with a distribution of aspect ratios and a low degree of interconnection. If, in the crust‐mantle transition region, zones of low p wave velocity (≦6 km/s) are correlated with those of high conductivity (≧0.08 S/m), melt fractions between 10 and 20% are likely and the degree of interconnection should be high. Thin films can be excluded as a dominant melt geometry in that region. Apart from improved constraints on melt geometry the results are in good agreement with published models based only on conductivity data. However, they disagree with published models based entirely on seismic data. The discrepancy is now resolved by the combined interpretation.