Open AccessSelf‐Reversal and Field Reversal in Palaeomagnetism
Author(s) -
Wright J. B.
Publication year - 1967
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.1967.tb03131.x
Subject(s) - paleomagnetism , geology , lava , igneous rock , geomagnetic reversal , natural remanent magnetization , volcanic rock , volcano , mineral , geochemistry , geophysics , polarity (international relations) , mineralogy , weathering , magnetic field , remanence , magnetization , materials science , chemistry , biochemistry , physics , quantum mechanics , cell , metallurgy
Summary This work arose out of investigations into the magnetic minerals of a Dunedin (New Zealand) lava suite, part of which is reversely magnetized. Results of those investigations are published elsewhere. Because of possible oxidation, whole rock Curie points are an unreliable guide to the identification of magnetic minerals, especially titanomagnetites in volcanic rocks, although this is often the only diagnostic criterion used. Oxidized titanomagnetite is common in igneous rocks and where it occurs the possibility of self‐reversal should be more seriously considered, especially as oxidation commonly takes place only after a considerable post‐eruption interval. Some normally magnetized rocks containing strongly oxidized titanomagnetites could have undergone self‐reversal after originally cooling in a reversed ambient field. Oxidation could also lead to self‐reversals in sediments containing detrital titanomagnetite. Self‐reversal is unlikely to have occurred in the Dunedin lavas, because their magnetic minerals are only weakly oxidized. The reversely magnetized part of the sequence was probably erupted during a reversed polarity episode between about 13 and 11 million years ago. The frequency of Cainozoic field reversals is briefly discussed.