| Title | 3D Temperature Model of the Hengill Geothermal Area (Iceland) Revealed from Electromagnetic Data |
|---|---|
| Authors | Viacheslav V. Spichak, Olga K. Zakharova and Alexandra G. Goidina |
| Year | 2011 |
| Conference | Stanford Geothermal Workshop |
| Keywords | geothermometer, Hengill, Iceland |
| Abstract | Application of the modified indirect EM geothermometer based on the joint using of the available MT and TEM data enabled constructing of the deep three-dimensional temperature model of the Hengill geothermal area. The temperature accuracy estimations indicate that at the lower boundary of the model, corresponding to the depths around 20km, the average relative errors are equal to 26.5%. The analysis of the temperature model has indicated that the lower boundary of the upper crust corresponding to the temperature of the brittle-to-ductile transition lies mainly at depths 15-20km. On the other hand, it is found that the solidus depth profile at the South Iceland Seismogenic Zone (SISZ) latitude agrees very well with the lower boundary of the EQ hypocenters, while the liquidus depth exceeds one determined from the linear extrapolation of the heat flow gradient measured in the boreholes. These findings mean that the crust in this area is more likely to be cool and thick than hot and thin. Basing on the temperature model it is possible to guess that the extremely high temperatures estimated in the studied area originate from the molten liquid magma (with temperatures higher than basalt liquidus) upwelling from the mantle and accumulating in the shallow reservoir (magma chamber) located at the western margin of the studied area. Its further leakage in the upper crust look like two magma flows with the diameter around 3-5km: the northern arm is extending towards the Nesjavellir and the southern one – to the Hellisheidu and Hveragerdi fields. The presence of a local heat source in the studied area explains the results of MT soundings, which have determined extremely well conducting layers at the depths corresponding to the locations of the high temperature intrusions. On the other hand, our results obtained for the Hengill geothermal area are in agreement with the hypothesis that shear wave attenuation in Icelandic crust is caused by local sources (in particular, by volcanoes) and is not diagnostic of the crust as a whole. |