Late miocene to late pleistocene geomagnetic secular variation at high-northern latitudes

We report a paleomagnetic study of Icelandic lavas of late Miocene to late Pliocene age to test the Geocentric Axial Dipole hypothesis at high-northern latitudes. Cores were sampled from 125 sites in the Fljótsdalur valley in eastern Iceland, and hand samples were taken for 17 new incremental heating ⁴⁰Ar/³⁹Ar age determinations. 96% of the cores were oriented using both a Brunton compass and a sun compass. Comparison of the magnetic and sun azimuths reveal a deviation of ±5○, ±10○ and ±20○, respectively, for 42%, 16% and 3% of the data points, indicating that core sampling intended for paleosecular variation (PSV) studies at high-northern latitudes should be oriented by sun. A total of 1279 independent specimens were subjected to AF- and thermal demagnetization for paleodirectional analysis, and well-grouped site mean directions were obtained for 123 sites of which 113 were found to be independent sites. Applying a selection criteria of k > 50 and N ≥ 5 (N_mean = 9.5), we obtain a combined grand mean direction for 46 normal and 53 reverse (for VGP_lat > ±45○) polarity sites of declination = 5.6○ and inclination = 77.5○ that is not significantly different from that expected from a GAD field. The corresponding paleomagnetic pole position (VGP_lat = 86.3○N, VGP_lon = 21.2○E, dp/dm = 4.0○/4.3○) is coincident with the North Pole within the 95% confidence limits. An updated age model is constructed based on the ⁴⁰Ar/³⁹Ar ages, showing that the majority of the Fljótsdalur lavas fall within 2-7 Ma. We combine the Fljótsdalur data with existing data from the nearby Jökuldalur valley. The 154 paleodirections are well-dispersed between 1-7 Ma and constitute a high-quality data set for PSV analysis. Our results partly support previous conclusions of a generally higher dispersion during reverse polarity intervals. However, when comparing our Matutayma data with Brunhes age data from Jan Mayen, we find no evidence of a higher VGP scatter during the Matuyama as previously suggested. When comparing our VGP scatter to the two commonly used models for VGP dispersion: Model G and TK03, we find a good fit for all 1-7 Ma VGP scatter data SB(1 − 7) to Model G, whereas S_{B(1 − 7)} is not fitted by TK03, even when considering the uncertainty of S_{B(1 − 7)}. We also find that all VGP scatter estimates, except that for the Gilbert subset, are consistent with Model G, while the discrepancy with TK03 is generally larger.