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Title: Unravelling magnetic mixtures in sediments, soils and rocks
Author: Peters, Clare
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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Measurements of initial susceptibility, remanent magnetisations and hysteresis loops have been carried out at room temperature on a range of characterised iron oxides and sulphides in order to attempt qualitative and quantitative identification of the individual minerals. The minerals studied were magnetite, titanomagnetite, haematite, pyrrhotite and greigite. It was found to be possible to qualitatively identify all the minerals (except titanomagnetites from magnetites) from each other using simple susceptibility and remanence ratios. Using discriminant analysis on both the remanence and hysteresis loop data, it was found to be possible to also distinguish the titanomagnetites from the magnetites purely on the basis of the room temperature measurements. The hysteresis loop data have been used in the development of least squares minimisation algorithms. Two minimisation methods have been devised. In the first method the end-members are the hysteresis loops of different minerals and different domain states (e.g. multi-domain magnetite and single-domain greigite). Each mineral used shows distinct hysteresis characteristics allowing a maximum of ten components to be identified. The algorithm, for the first time, is able to reliably quantify paramagnetic components in natural samples. It can also distinguish between superparamagnetic and multi-domain magnetite using only room temperature hysteresis loop data. Secondly sediment sources (e.g. topsoils and subsoils) have been used to unmix natural sediments. The newly developed qualitative and quantitative methods have been applied to a range of sites. Mineral unmixing of the Papa Westray soils and also soils from the archaeological site Kissonerga-Mosphilia, Cyprus, indicate that the dominant magnetic domain state in the samples is superparamagnetic. The use of three independent magnetic identification techniques (qualitative, quantitative and thermomagnetic) have confirmed the presence of both magnetite and pyrrhotite grains in deep crustal rocks from the German KTB pilot borehole core.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available