Magnetic Investigation of the hydrothermal system of the Krafla geothermal area

february-july 2021

The Krafla geothermal area is located within a large caldera crossed by a fissure zone and is characterized by intense heat flow and hydrothermal alteration associated to the presence of magma at a 2 km depth as evidenced accidentally during geothermal drilling (e.g. Arnason et al., 2020). The area has been extensively studied with various geophysical imaging methods and drilling. In this study, we will use the aeromagnetic survey flown over the caldera that shows a large magnetic low over the geothermal area. This magnetic low suggests a decrease of magnetization at depth that could be associated either to a thinner magnetic layer due to a shallower Curie temperature, temperature above which rocks lose their magnetization, or to the presence of weakly-magnetic intensely-altered volcanic rocks (Olivia-Urcia et al., 2011). In order to distinguish the contribution of temperature and alteration in the magnetic signal, the data will be interpreted by constructing forward and inverse models and will incorporate information from magnetic properties measured on drill hole samples and other geophysical data such as a resistivity model deduced from magneto-telluric data and transitional electromagnetic soundings and temperature data measured in drill holes. The resistivity model will provide preliminary information on the distribution of alteration whereas temperature will be used to obtain a preliminary estimation of the depth to the Curie temperature isotherm. During the internship, the student will perform the analysis and interpretation of the magnetic data by writing and using existing matlab or python scripts as well as using a software specialized in the processing and modeling of magnetic surveys. The student might be involved at the end of the internship in a 10 day field work session in Krafla where new drone-borne magnetic surveys will be acquired to complement the current dataset with a much higher resolution dataset.

Arnason, K., New Conceptual Model for the Magma- Hydrothermal-Tectonic System of Krafla, NE Iceland, Geosciences 2020, 10, 34 ; doi:10.3390/geosciences10010034

Oliva-Urcia, B., Kontny, A., Vahle, C., & Schleicher, A. M. (2011). Modification of the magnetic mineralogy in basalts due to fluid–rock interactions in a high-temperature geothermal system (Krafla, Iceland). Geophysical Journal International, 186(1), 155-174.