PALAEOMAGNETIC AND ROCK MAGNETIC STUDIES ON SOME PRECAMBRIAN ROCKS, EASTERN DESERT, EGYPT

Abstract

When a magnetic field is applied to any substance it induces a magnetization (M) which is directly related to the strength of the applied field (H), with a constant of proportionality being known the magnetic susceptibility (K). The magnetization (M) is thus defmed as: M=KH

The magnetization of a mineral consists of two types: remanent and induced magnetization. The latter is only present when the mineral is under the influence of an applied field (which includes the earth's magnetic field). Diamagnetic minerals produce an induced magnetization opposite to the applied field i.e., (-ve) susceptibility. Paramagnetic minerals produce an induced magnetization in the same direction as the applied field i.e., (+ve) susceptibility. Certain few minerals have much stronger positive susceptibilities than the paramagnetic minerals and may also carry a strong remanent magnetization (ferromagnetic minerals). Such a spontaneous magnetization only arises if the ambient temperature is below the Curie temperature. The direction of the remanence will be . parallel (or occasionally anti-parallel) to the ambient field, it can therefore

be used to infer the direction of the earth's field at the time of acquisition.