What Rock Magnetism Reveals Of The Karoo Basin

A comparative study of the variation in magnetic properties in eight boreholes situated across the Karoo Basin was performed. Four of these boreholes incepted one or more dolerite sills. The aim of this study is to determine the thermal impact of the magma intrusions on the surrounding sediments by using several magnetic experiments. The methods that will be discussed include low field anisotropy of magnetization (LFAMS), magneto-stratigraphy using the classic baked contact test, as well as the magnetic alteration index (A40). Re-magnetization due to the heating effect of the dolerite intrusions are limited to short distances within the contact aureole. Those boreholes that intersect dolerite sills indicate that the heating effect occurred no wider than half of the sill thicknesses. These results also suggest a widespread elevation in the geomagnetic temperatures of the Karoo stratigraphic sequence to temperatures above 150 °C that gradually increases from southwest to northeast across the Karoo Basin.