Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature
Abstract Absolute paleointensity (API) of the geomagnetic field can be estimated from volcanic rocks by comparing the natural remanent magnetization (NRM) to a laboratory‐induced thermoremanent magnetization (Lab‐TRM). Plots of NRM unblocking versus Lab‐TRM blocking from API experiments often exhibi...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Wiley
2022-04-01
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| Series: | Geochemistry, Geophysics, Geosystems |
| Online Access: | https://doi.org/10.1029/2022GC010391 |
| _version_ | 1827771679996116992 |
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| author | Y. Yamamoto L. Tauxe H. Ahn C. Santos |
| author_facet | Y. Yamamoto L. Tauxe H. Ahn C. Santos |
| author_sort | Y. Yamamoto |
| collection | DOAJ |
| description | Abstract Absolute paleointensity (API) of the geomagnetic field can be estimated from volcanic rocks by comparing the natural remanent magnetization (NRM) to a laboratory‐induced thermoremanent magnetization (Lab‐TRM). Plots of NRM unblocking versus Lab‐TRM blocking from API experiments often exhibit nonideal curvature, which can result in biased estimates. Previous work showed that curvature can increase with age; however, selection criteria designed to eliminate such behavior yielded accurate estimates for two‐year‐aged specimens (70.3 ± 3.8 μT; N = 96 specimens out of 120 experiments). API can also be estimated in coercivity space. Here, we use the Tsunakawa‐Shaw (TS) method applied to 20 specimens aged in the laboratory field of 70.0 μT for 4 years, after acquisition of zero‐age (fresh) Lab‐TRM in the same field. Selection criteria for the TS experiment also yielded accurate results (68.5 ± 4.5 μT; N = 17 specimens). In thermal API experiments, curvature is related to internal structure with more single domain‐like behavior having the least curvature. Here we show that the fraction of anhysteretic remanent magnetization demagnetized by low‐temperature treatment was larger for samples with larger thermal curvatures suggesting a magnetocrystalline anisotropy source. We also tested experimental remedies that have been proposed to improve the accuracy of paleointensity estimates. In particular, we test the efficacy of the multi‐specimen approach and a strategy pretreating specimens with low field alternating field demagnetization prior to the paleointensity experiment. Neither yielded accurate results. |
| first_indexed | 2024-03-11T12:57:38Z |
| format | Article |
| id | doaj.art-87ead1a1f06643aaa733923669e2f9d7 |
| institution | Directory Open Access Journal |
| issn | 1525-2027 |
| language | English |
| last_indexed | 2024-03-11T12:57:38Z |
| publishDate | 2022-04-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj.art-87ead1a1f06643aaa733923669e2f9d72023-11-03T16:56:16ZengWileyGeochemistry, Geophysics, Geosystems1525-20272022-04-01234n/an/a10.1029/2022GC010391Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” CurvatureY. Yamamoto0L. Tauxe1H. Ahn2C. Santos3Kochi University Kochi JapanScripps Institution of Oceanography La Jolla CA USAKorea Institute of Geoscience and Mineral Resources Daejeon Republic of KoreaScripps Institution of Oceanography La Jolla CA USAAbstract Absolute paleointensity (API) of the geomagnetic field can be estimated from volcanic rocks by comparing the natural remanent magnetization (NRM) to a laboratory‐induced thermoremanent magnetization (Lab‐TRM). Plots of NRM unblocking versus Lab‐TRM blocking from API experiments often exhibit nonideal curvature, which can result in biased estimates. Previous work showed that curvature can increase with age; however, selection criteria designed to eliminate such behavior yielded accurate estimates for two‐year‐aged specimens (70.3 ± 3.8 μT; N = 96 specimens out of 120 experiments). API can also be estimated in coercivity space. Here, we use the Tsunakawa‐Shaw (TS) method applied to 20 specimens aged in the laboratory field of 70.0 μT for 4 years, after acquisition of zero‐age (fresh) Lab‐TRM in the same field. Selection criteria for the TS experiment also yielded accurate results (68.5 ± 4.5 μT; N = 17 specimens). In thermal API experiments, curvature is related to internal structure with more single domain‐like behavior having the least curvature. Here we show that the fraction of anhysteretic remanent magnetization demagnetized by low‐temperature treatment was larger for samples with larger thermal curvatures suggesting a magnetocrystalline anisotropy source. We also tested experimental remedies that have been proposed to improve the accuracy of paleointensity estimates. In particular, we test the efficacy of the multi‐specimen approach and a strategy pretreating specimens with low field alternating field demagnetization prior to the paleointensity experiment. Neither yielded accurate results.https://doi.org/10.1029/2022GC010391 |
| spellingShingle | Y. Yamamoto L. Tauxe H. Ahn C. Santos Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature Geochemistry, Geophysics, Geosystems |
| title | Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature |
| title_full | Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature |
| title_fullStr | Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature |
| title_full_unstemmed | Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature |
| title_short | Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature |
| title_sort | absolute paleointensity experiments on aged thermoremanent magnetization assessment of reliability of the tsunakawa shaw and other methods with implications for fragile curvature |
| url | https://doi.org/10.1029/2022GC010391 |
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