Open AccessA New Index of Palaeomagnetic Stability for Magnetite Bearing Igneous Rocks
Author(s) -
Giddings J. W.,
McElhinny M. W.
Publication year - 1976
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.1976.tb00284.x
Subject(s) - magnetite , remanence , coercivity , igneous rock , geology , demagnetizing field , stability (learning theory) , rock magnetism , magnetic field , geophysics , mineralogy , magnetization , condensed matter physics , physics , geochemistry , computer science , paleontology , quantum mechanics , machine learning
Summary Confusion has existed in the palaeomagnetic literature over the use of the term ‘magnetic stability’. Attempts have been made to derive ‘stability indexes’ which do not have the function of describing all the factors affecting the magnetic stability of a rock, but merely define when the process of magnetic cleaning has been optimized for the purpose of obtaining palaeodirections. Such indexes are better described as ‘optimum cleaning indexes’. The overall palaeomagnetic stability of a rock specimen can be derived from the complete alternating field demagnetization characteristics. In addition to a parameter that defines the point of optimum cleaning the characteristics of the coercivity spectrum need to be formulated. The important parameters are the proportion of the coercivity spectrum occupied by secondary components and the maximum alternating field the grains can withstand (related to the maximum time stability of the grains). For this purpose we define the Stable Range of alternating fields over which the cleaned remanence is directionally consistent. Using these parameters we define a new palaeomagnetic stability index (PSI) for magnetite bearing igneous rocks whose magnitude ranges from 1 (extremely stable) to 0 (unstable). The index is especially useful in comparing the overall behaviour of one suite of rocks with another and could be used as an indicator in studies concerned with the fundamental control of magnetic stability.