Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes
We report a palaeomagnetic 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 heati...
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Online Access: | http://hdl.handle.net/10044/1/78993 https://doi.org/10.1093/gji/ggaa148 |
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ftimperialcol:oai:spiral.imperial.ac.uk:10044/1/78993 2023-05-15T16:53:08+02:00 Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes Døssing, A Riishuus, MS Mac Niocaill, C Muxworthy, AR Maclennan, J 2020-03-17 http://hdl.handle.net/10044/1/78993 https://doi.org/10.1093/gji/ggaa148 en eng Oxford University Press (OUP) Geophysical Journal International 0956-540X http://hdl.handle.net/10044/1/78993 doi:10.1093/gji/ggaa148 © The Author(s) 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) 102 86 0403 Geology 0404 Geophysics 0909 Geomatic Engineering Geochemistry & Geophysics Journal Article 2020 ftimperialcol https://doi.org/10.1093/gji/ggaa148 2020-05-14T22:38:25Z We report a palaeomagnetic 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 per cent of the cores were oriented using both a Brunton compass and a sun compass. Comparison of the magnetic and sun azimuths reveals deviations of ±5°, ±10° and ±20°, respectively, for 42, 16 and 3 per cent of the data points, indicating that core sampling intended for palaeosecular 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 palaeodirectional 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 (Nmean = 9.5), we obtain a combined grand mean direction for 46 normal and 53 reverse (for VGPlat > ±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 palaeomagnetic pole position (VGPlat = 86.3°N, VGPlon = 21.2°E, dp/dm = 4.0°/4.3°) is coincident with the North Pole within the 95 per cent 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 palaeodirections are well-dispersed between 1 and 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 SB(1–7) is not fitted by TK03, even when considering the uncertainty of SB(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. Article in Journal/Newspaper Iceland Jan Mayen North Pole Imperial College London: Spiral Jan Mayen Jökuldalur ENVELOPE(-13.886,-13.886,65.510,65.510) North Pole Geophysical Journal International 222 1 86 102 |
institution |
Open Polar |
collection |
Imperial College London: Spiral |
op_collection_id |
ftimperialcol |
language |
English |
topic |
0403 Geology 0404 Geophysics 0909 Geomatic Engineering Geochemistry & Geophysics |
spellingShingle |
0403 Geology 0404 Geophysics 0909 Geomatic Engineering Geochemistry & Geophysics Døssing, A Riishuus, MS Mac Niocaill, C Muxworthy, AR Maclennan, J Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes |
topic_facet |
0403 Geology 0404 Geophysics 0909 Geomatic Engineering Geochemistry & Geophysics |
description |
We report a palaeomagnetic 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 per cent of the cores were oriented using both a Brunton compass and a sun compass. Comparison of the magnetic and sun azimuths reveals deviations of ±5°, ±10° and ±20°, respectively, for 42, 16 and 3 per cent of the data points, indicating that core sampling intended for palaeosecular 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 palaeodirectional 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 (Nmean = 9.5), we obtain a combined grand mean direction for 46 normal and 53 reverse (for VGPlat > ±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 palaeomagnetic pole position (VGPlat = 86.3°N, VGPlon = 21.2°E, dp/dm = 4.0°/4.3°) is coincident with the North Pole within the 95 per cent 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 palaeodirections are well-dispersed between 1 and 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 SB(1–7) is not fitted by TK03, even when considering the uncertainty of SB(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. |
format |
Article in Journal/Newspaper |
author |
Døssing, A Riishuus, MS Mac Niocaill, C Muxworthy, AR Maclennan, J |
author_facet |
Døssing, A Riishuus, MS Mac Niocaill, C Muxworthy, AR Maclennan, J |
author_sort |
Døssing, A |
title |
Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes |
title_short |
Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes |
title_full |
Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes |
title_fullStr |
Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes |
title_full_unstemmed |
Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes |
title_sort |
late miocene to late pleistocene geomagnetic secular variation at high northern latitudes |
publisher |
Oxford University Press (OUP) |
publishDate |
2020 |
url |
http://hdl.handle.net/10044/1/78993 https://doi.org/10.1093/gji/ggaa148 |
long_lat |
ENVELOPE(-13.886,-13.886,65.510,65.510) |
geographic |
Jan Mayen Jökuldalur North Pole |
geographic_facet |
Jan Mayen Jökuldalur North Pole |
genre |
Iceland Jan Mayen North Pole |
genre_facet |
Iceland Jan Mayen North Pole |
op_source |
102 86 |
op_relation |
Geophysical Journal International 0956-540X http://hdl.handle.net/10044/1/78993 doi:10.1093/gji/ggaa148 |
op_rights |
© The Author(s) 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) |
op_doi |
https://doi.org/10.1093/gji/ggaa148 |
container_title |
Geophysical Journal International |
container_volume |
222 |
container_issue |
1 |
container_start_page |
86 |
op_container_end_page |
102 |
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1766043643921039360 |