Magnetotelluric Imaging of the Upper Mantle Conductivity in Iceland: Investigating Signs of Partial Melt Due to Glacial Uplift

We present results from a magnetotelluric (MT) study conducted as a pilot project, investigating the electrical structure of the partial melt at the crust-mantle boundary beneath central Iceland. With an ongoing thinning of the Vatnajökull ice cap, located above the mantle plume head, the lithosphere experiences uplift and decompression. Due to the unloading, the promotion of partial melting in the upper mantle is expected, potentially increasing volcanic activity. This partial melt zone in the asthenosphere generates a conductive zone that long-period MT methods can detect. These results could provide new perspectives on partial melt at the crust-mantle boundary beneath Iceland, complementing existing seismic and gravity observations, and contributing to the discussion of plume-lithosphere interactions.

Long-period MT data were acquired during a field campaign in August-September 2025 along a ~200 km east-west profile, perpendicular to the plate boundary, with ~50 km station spacing. Time-series data from four stations were processed using single-station and remote-reference techniques following the Frankfurt MT (FFMT) software in MATLAB. The preliminary results show two conductive layers, one indicating the deep conductive layer at depths of 5-20 km, previously identified in Icelandic MT studies. A second, deeper low-resistivity zone is observed and interpreted as a possible signature of the crust-mantle transition or partial melt accumulation in the upper mantle. 3D forward models of the data will be conducted to display how the responses would change with anomalies at different depths. In addition, a literature study on the petrophysical properties of magma in porous rocks will be carried out to constrain our interpretations, linking resistivity and porosity under varying pressure and temperature conditions. Together, these results will evaluate whether a decompressional-induced partial melting beneath central Iceland is detectable using long-period MT methods, with implications for mantle plume dynamics.