High northern geomagnetic field behavior and new constraints on the Gilsá event: Paleomagnetic and 40Ar/39Ar results of ∼0.5–3.1 Ma basalts from Jökuldalur, Iceland

• Published in: Earth and Planetary Science Letters
• Main Authors: MacNiocaill, C, Dossing, A, Muxworthy, A, Supakulopas, R, Riishuus, M
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2016
• Subjects: Jökuldalur; North Pole; Iceland
• Online Access: https://doi.org/10.1016/j.epsl.2016.09.022; https://ora.ox.ac.uk/objects/uuid:5008aa2e-fb66-4edb-9b3d-7cf1f5c537e7

Recent paleomagnetic results of extrusive rocks from high southern latitudes (> 60°S) and high northern latitudes (> 60°N) have been suggested to reflect a hemispheric asymmetry of the geomagnetic field on time-scales of 105 to 106 years, with higher and more stable fields in the north. This interpretation, however, is based on only a few modern-standard paleodirectional data sets and on high northern stable field paleointensity data of rocks that are mainly younger than 100 kyr. The sparsity of modern-standard data questions the validity (and age range) of this potential geomagnetic asymmetry. In 2013 and 2014, we sampled basaltic lava ows in Jokuldalur, north-eastern Iceland,to obtain high-standard paleodirectional and paleointensity data at relatively high-northern latitudes (65.2°N). On average, we sampled >15 cores per site at 51 sites of predominantly Matuyama age. Complete demagnetization was carried out on all samples using AF or thermal demagnetization. We present 45 distinct paleomagnetic directions based on overall N > 10 ChRMs per site and α95 < 3:5°. We obtain a mean direction of D =355.7°, I =76.3°,and α95 =3.2 for N =45 sites that is not significantly different from a GAD field. The resulting 45 VGPs distribute around the North Pole, and the global mean paleomagnetic pole (λ = 87:8°, Φ = 224:3°) is coincident with the North Pole within the α95 confidence limit. We calculate a VGP dispersion for our 38 Matuyama age sites of 20:523:3 17:8 , which is ~1-4° lower than estimates from published Iceland data (from surveys that sampled 2-5 cores per site) but still supports the interpretation of a dependence of VGP dispersion on latitude during the Matuyama. Based on relatively strict cut-off criteria we also present six new field strength estimates from the time interval ~1.2-1.83 Ma, thus filling a large data gap of the high-northern stable field behaviour. We obtain a median VADM of 57±3 ZAm2 (VDM of 60±5 Am2), which is higher than the median VADM of 16 intensity estimates from ...