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Title: A palaeomagnetic study of Tertiary and Devonian igneous rocks from Britain
Author: McMurry, Earl William
ISNI:       0000 0004 2693 9323
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1968
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Theoretical angular dispersion curves were produced from a model of the geomagnetic field in which parameters such as dipole wobble, dipole moment, and secular variation could vary independently of each other. Comparison with palaeomagnetic data suggested that the average geomagnetic field could be characterised by moderate dipole wobble and secular variation effects somewhat reduced compared with that of today. Palaeomagnetic results from normally and reversely magnetized Tertiary igneous formations are presented. Baked contact studies indicate the reality of field reversal which occurred in Palaeocene times according to K-Ar dates from 3 normal dykes. The overall mean pole position differs marginally from the present rotation axis. Lavas which had been baked by dyke intrusion were studied. In general, samples from the baked zone were magnetically harder, more intense, mare stable and directionally better grouped than those from the dyke or unbaked lava. Lower Devonian lavas from two separate regions of Scotland were investigated. The reliability of the palaeomagnetic results was established using laboratory and Fold Test evidence. Normal and reversed groups were found whose directions indicate that the sampled region was about 30° south in Lower Devonian times. Comparison of these results with other Devonian studies from Britain, Europe and Asia shows that the British results are internally consistent and significantly different from those for Eurasian sediments, it has been suggested that this difference may be due to large scale regional remagnetization of the sediments in Permo-Carboniferous times. This suggestion is examined in detail. It is found that the suggestion offers a likely explanation for some of the results but not for most. Alternatively, it is suggested that the Middle Devonian was a time of rapid polar movement relative to the rotation axis. This is consistent with the palaeomagnetic results from Britain, Europe and Asia, and also with results which have been found for the Southern Hemisphere as well.
Supervisor: Blackett, P. M. S. Sponsor: Natural Environment Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available