Magnetic Characteristics, Eruption Frequency and Magnetostratigraphy for the Lava Sequence in Brunnardalur in Southeast Iceland

Sammanfattning

Magnetic remanence carried by basaltic lava sequences in Iceland is of significant interest when studying the emplacement of lava flows, frequency of eruptions, and for reconstructing historic geomagnetic variations. Previous research has focused on sequential lava flows on Eastern Iceland. However, similar basaltic formations are found in Southeast Iceland, currently posing a gap in existing literature with sparse geological and palaeomagnetic mapping of the area. Additional studies on the lava sequences of Iceland are of importance for better understanding the behaviours of volcanic systems that influence present-day volcanism. The aim of this project was to investigate whether indications of magnetic reversals are present within the sequential lava flows in Brunnardalur in Southeast Iceland, and to determine the frequency of eruptions. In addition to a magnetostratigraphic column, several stereographic projections were produced. For investigating the magnetic properties of the sample suite, a spinner magnetometer, a Kappabridge, thermomagnetic analysis and alternating field demagnetization were used. The natural remanent magnetization, mass-normalised bulk susceptibility and thermomagnetic properties were measured, enabling the construction of virtual geomagnetic poles. There were no indications of substantial magnetic reversals in the lava pile. However, the sample suite exhibits variations in magnetic properties, pointing to possible hydrothermal, viscous or chemical overprint. The eruption frequency was determined to be one eruption every 4000-4500 years, suggestinga relatively high frequency of flows compared to other areas of Eastern Iceland.