dorsal/arxiv
View SchemaMono Lake or Laschamp geomagnetic event recorded from lava flows in Amsterdam Island (southeastern Indian Ocean)
| Authors | Claire Carvallo, Pierre Camps, Gilles Ruffet, Bernard Henry, Thierry Poidras |
|---|---|
| Categories | |
| ArXiv ID | physics/0304061 |
| URL | https://arxiv.org/abs/physics/0304061 |
| DOI | 10.1046/j.1365-246X.2003.01993.x |
| Journal | Geophysical Journal International 154 (2003) 767-782 |
Abstract
We report a survey carried out on basalt flows from Amsterdam Island in order to check the presence of intermediate directions interpreted to belong to a geomagnetic field excursion within the Brunhes epoch, completing this paleomagnetic record with paleointensity determinations and radiometric dating. The directional results corroborate the findings by Watkins and Nougier (1973) : normal polarity is found for two units and an intermediate direction, with associated VGPs close to the equator, for the other two units. A notable result is that these volcanic rocks are well suited for absolute paleointensity determinations. Fifty percent of the samples yields reliable intensity values with high quality factors. An original element of this study is that we made use of the PTRM-tail test of Shcherbakova et al. (2000) to help in the interpretation of the paleointensity measurements. Doing thus, only the high temperature intervals, beyond 400 degres C, were retained to obtain the most reliable estimate of the strength of the ancient magnetic field. The normal units yield Virtual Dipole Moments (VDM) of 6.2 and 7.7 10e22 Am2 and the excursional units yield values of 3.7 and 3.4 10e22 Am2. These results are quite consistent with the other Thellier determinations from Brunhes excursion records, all characterized by a decrease of the VDM as VGP latitude decreases. 40Ar/39Ar isotopic age determinations provide an estimate of 26+-15 Kyr and 18+-9 Kyr for the transitional lava flows, which could correspond to the Mono Lake excursion. However, the large error bars associated with these ages do not exclude the hypothesis that this event is the Laschamp.
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"abstract": "We report a survey carried out on basalt flows from Amsterdam Island in order\nto check the presence of intermediate directions interpreted to belong to a\ngeomagnetic field excursion within the Brunhes epoch, completing this\npaleomagnetic record with paleointensity determinations and radiometric dating.\nThe directional results corroborate the findings by Watkins and Nougier (1973)\n: normal polarity is found for two units and an intermediate direction, with\nassociated VGPs close to the equator, for the other two units. A notable result\nis that these volcanic rocks are well suited for absolute paleointensity\ndeterminations. Fifty percent of the samples yields reliable intensity values\nwith high quality factors. An original element of this study is that we made\nuse of the PTRM-tail test of Shcherbakova et al. (2000) to help in the\ninterpretation of the paleointensity measurements. Doing thus, only the high\ntemperature intervals, beyond 400 degres C, were retained to obtain the most\nreliable estimate of the strength of the ancient magnetic field. The normal\nunits yield Virtual Dipole Moments (VDM) of 6.2 and 7.7 10e22 Am2 and the\nexcursional units yield values of 3.7 and 3.4 10e22 Am2. These results are\nquite consistent with the other Thellier determinations from Brunhes excursion\nrecords, all characterized by a decrease of the VDM as VGP latitude decreases.\n40Ar/39Ar isotopic age determinations provide an estimate of 26+-15 Kyr and\n18+-9 Kyr for the transitional lava flows, which could correspond to the Mono\nLake excursion. However, the large error bars associated with these ages do not\nexclude the hypothesis that this event is the Laschamp.",
"arxiv_id": "physics/0304061",
"authors": [
"Claire Carvallo",
"Pierre Camps",
"Gilles Ruffet",
"Bernard Henry",
"Thierry Poidras"
],
"categories": [
"physics.geo-ph"
],
"doi": "10.1046/j.1365-246X.2003.01993.x",
"journal_ref": "Geophysical Journal International 154 (2003) 767-782",
"title": "Mono Lake or Laschamp geomagnetic event recorded from lava flows in Amsterdam Island (southeastern Indian Ocean)",
"url": "https://arxiv.org/abs/physics/0304061"
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