A comparative analysis of the magnetic anomalies associated with the geothermal systems on Reykjanes peninsula
Author: Jillian Mary Verbeurgt
Year: 2019
Supervisor: Haraldur Auðunsson
Abstract:
Extensive aeromagnetic surveying was initiated by Þorbjörn Sigurgeirsson in 1968 (Jónsson, Kristjansson, & Sverrisson, 1991). This aeromagnetic data reveals a normally polarized band on the Reykjanes peninsula, formed during the Brunhes chron, with reversely polarized bands on each side, formed during the Matuyama chron. The rocks from the Brunhes chron contain negative magnetic anomalies within positively magnetized fissured swarms. These anomalies have been speculated to be due to shallow structures like buried hyaloclastite formations or high temperature activity destroying magnetite (Kristjánsson & Jónsson, 2017).
Surface magnetic data was collected for four of the geothermal systems on the peninsula, including Reykjanes, Eldvörp, Svartsengi, and Brennisteinsfjöll. This data was filtered through upward continuation to remove the noise due to surface lavas. The surface profiles were then analyzed. A comparative analysis of surface magnetic data for the geothermal systems on the Reykjanes peninsula was completed to identify similarities of the systems. These were also compared to the existing geological, aeromagnetic, and resistivity data for the area.
The surface magnetic data was analyzed and two of the areas showed magnetic lows where geothermal activity is observed with intensities ranging from 670 to 1700 nT. Simple models were created for these two areas to determine the contrast in magnetization due to geothermal activity. These models were based off a simple sphere. Resistivity data was used to determine the depth to the top of the sources. The radii for the spherical models was determined by subtracting the top of the source from the depth to the center of the source. These were found to be just over 2000 m for Svartsengi and just over 1500 m for Brennisteinsfjöll. The models for Svartsengi and Brennisteinsfjöll showed a decreased magnetization between 2.5 and 8.5 A/m. The surface survey data for the Eldvörp area did not show a significant magnetic anomaly. Most of the surveying for Eldvörp and Reykjanes included shorth profiles that better show short wavelength anomalies. The anomalies observed in the surface magnetics were consistent with the resistivity and aeromagnetic data for each area.
There are limitations in surface magnetic surveying due to the noise incurred due to the surface lavas. Upward continuation was applied to reduce some of this noise; there is the possibility of losing meaningful data if too much noise reduction is applied. In future work, it would be useful to accommodate gridded data over the geothermal areas in interest. This way 3D analysis could be performed. This would allow for a map showing the entire lateral extent to the anomaly. A more complete picture could be gained from drill chip sampling and characterization of magnetic minerals would be useful in validating models.