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  • 1
    facet.materialart.
    Unknown
    In:  Earth Planets and Space
    Publication Date: 2020-02-12
    Description: The thermal fluctuation field (H-f) is central to thermoremanent acquisition models, which are key to our understanding of the reliability of palaeomagnetic data, however, Hf is poorly quantified for natural systems. We report H-f determinations for a range of basalts, made by measuring rate-dependent hysteresis. The results for the basalts were found to be generally consistent within the space of Hf versus the coercive force H-C, i.e., the "Barbier plot", which is characterized by the empirically derived relationship; log H-f proportional to 1.3 log H-C obtained from measurements on a wide range of different magnetic materials. Although the basalts appear to occupy the correct position within the space of the Barbier plot, the relationship within the sample set, log H-f proportional to 0.54 log H-C, is different to the Barbier relationship. This difference is attributed to the original Barbier relationship being derived from a wide range of different synthetic magnetic materials, and not for variations within one material type, as well as differences in methodology in determining H-f. We consider the relationship between H-C and the activation volume, nu(act) which was found to be H-C proportional to nu(-0.68)(act) for our mineralogically homogeneous samples. This compares favourably with theoretical predictions, and with previous empirical estimates based oil the Barbier plot, which defined the relationship as H-C proportional to nu(-0.73)(act).
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 2
    Publication Date: 2020-02-12
    Description: This paper reports an empirical test of a new nonheating Preisach-based protocol for determining the absolute ancient magnetic field intensity (paleointensity) using a selection of synthetic samples and a large suite of modern lavas and pyroclastic lithic samples. Generally, the Preisach paleointensity estimates compare favorably with the expected field intensities: (1) for the synthetic samples displaying single-domain-like behavior, the method returned the correct result for the known field, while multidomain samples yielded an underestimate, and (2) averaging 168 post-1850 A.D. lavas yielded a value 〈6% within the expected field value. These Preisach paleointensity estimates are also compared with paleointensity determinations made on the same suite of samples using standard Thellier-type heating protocols and the nonheating remanence (REM) method. The Preisach paleointensity estimates compare favorably for samples that yielded correct Thellier-type determinations, including the synthetic single-domain-like samples. In addition, the Preisach method produced estimates for cases where the Thellier-type estimates failed. A possible selection criterion was identified (median destructive field), which was found to improve the paleointensity estimates in some sample suites. For the investigated sample set the Preisach method was found to be much more accurate than the REM method. The importance of cooling rate on the Preisach paleointensity estimate is also examined.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 3
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    Unknown
    In:  EOS, Transactions, American Geophysical Union, Suppl. ; 88 (52)
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/conferenceObject
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