Open AccessA Palaeomagnetic Study of the Mull Regional Dyke Swarm
Author(s) -
AdeHall J. M.,
Dagley P.,
Wilson R. L.,
Evans A.,
Riding A.,
Smith P. J.,
Skelhorne R.,
Sloan T.
Publication year - 1972
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1972.tb06106.x
Subject(s) - geology , swarm behaviour , geochemistry , hydrothermal circulation , geophysics , earth science , seismology , mathematics , mathematical optimization
Summary A detailed palaeomagnetic investigation has been made of the Mull (Scotland) regional dyke swarm. 165 dykes were sampled in a 7‐km section across the swarm from Quinish to Ardmore in northern Mull. A major question arising from the results of the investigation is whether the cleaned NRM directions for the dykes are equivalent to the original cooling TRM directions. The question arises since evidence from several lines shows that the dykes have experienced considerable hydrothermal alteration, with reheating temperatures averaging 200°C and major changes in the iron titanium oxides responsible for the NRM. Surprisingly, the answer appears to be that original cooling TRM directions are probably still well represented by cleaned NRM directions. Notwithstanding the large number of palaeomagnetic directions obtained from the dykes, no simple picture of the Palaeogene geomagnetic field emerges. Thus, continental drift cannot be estimated from the data. The explanation for the distribution of directions appears to rest between either a short time of activity for the whole British Tertiary igneous province with non‐representative sampling by the activity in individual areas, or the existence of relatively long periods of non‐centred axial dipole behaviour for the geomagnetic field during the Palaeogene.