[SEM18-P12] The time-averaged palaeomagnetic field during 3-7 Ma at high northern latitudes
Keywords:Iceland, Geocentric Axial Dipole (GAD) hypothesis, Palaeomagnetism
The demagnetisation measurements including alternating field (AF) and thermal were made to determine palaeomagnetic directions. In order to improve quality of high-latitude data, approximately 6-10 directional data per site were used to calculate mean directions. We found mean declination and inclination of 355.0° and 72.0° with 95% confidential limit of 2.2°. The modelling of the field was performed by adding 4% of quadrupole and 11% of octupole to the model; the model returns the inclination of 72.1° at 65°N. Our dataset passed the reversal test with Class A which is indicative of high accuracy. The directional data were converted to virtual geomagnetic pole (VGP) which is located at 81.3°N and 180.2°E.
The Curie temperature determination was performed using strong field thermomagnetic analysis prior to palaeointensity experiment. Evidence from strong field thermomagnetic curves indicates the presence of Ti-rich titanomagnetite, Fe-rich titanomagnetite and titanomaghemite in samples across the lava flows. Palaeointensity experiment was conducted in a helium atmosphere in order to prevent oxidation on the samples. We used the infield/zero-field and zero-field/infield protocol with partial thermoremanent magnetisation (pTRM) checks. Samples from 20 lava flows yield successful results. We found the mean intensity of 22.0±2.7µT, which is lower than the intensity of the GAD field (55.9 µT) at 65°N, and the virtual dipole moment (VDM) of 32 ZAm2. The investigation of palaeomagnetic data from Icelandic basalts reveals that the non-dipole field persists during 3-7 Ma at high-northern latitudes. However, the results of this study should be compared with the time-averaged field data at high-southern latitudes especially at 65°S to see the symmetry of the field during 3-7 Ma.