A new conceptual model of the Icelandic crust in the Hengill geothermal area based on the indirect electromagnetic geothermometry

Abstract

Application of the indirect electromagnetic geothermometer calibrated by available temperature well logs has enabled the construction of the three-dimensional temperature model of the Hengill geothermal area (Iceland) up to a depth of 20km. Its analysis showed that the background temperature of the Icelandic crust above 20km does not exceed 400°С. It is overlapped by a network of interconnected high-temperature low resistive channels, which braid through the crust mainly at a level of 10–15km and root to a depth greater than 20km. Accordingly, the probable heat sources feeding the geothermal system are supposed to be the intrusions of the hot partially molten magma upwelling from the mantle through faults and fractures. The comparison between the vertical temperature cross-sections and the projections of the earthquake hypocenters showed that they all are located in the areas where temperature does not exceed 400°С, which is a gabbro solidus in a silica-rich Icelandic crust. Joint analysis of the temperature model together with the resistivity and residual Bouguer gravity anomalies enabled us to explain the distribution of the earthquake hypocenters by different geothermal regimes in adjacent parts of the area and cooling of large massifs of the partially molten solidified magma beneath seismically active areas. Basing on the above inferences, we suggest a new self-consistent conceptual model of the Icelandic crust, which agrees with most of the previous geophysical results and provides an explanation for the facts that the previous models failed to explain.