The magnetic susceptibility of granitic rocks as a proxy for geochemical composition: Example from the Saruhan granitoids, NE Turkey

Abstract

The magnetic susceptibility of rocks is determined by their bulk chemistry and magnetic mineralogy. In this case study of the Saruhan pluton in Turkey, a detailed survey based on 925 field measurements and 37 whole rock analyses, reveals a strong correlation between magnetic susceptibility and FeO t ( R 2 = 0.8). Petrographic observations and calculations based on whole-rock major element analyses indicate the presence of magnetite grains. Further calculations show that magnetite accounts for 88% of the magnetic susceptibility. The spatial correlation between FeO total and the magnetic susceptibility is particularly spectacular which suggests that K m is a proxy for geochemical differentiation. The zoning pattern of magnetic susceptibility across the pluton is concentric and reverse, with the highest values of magnetic susceptibility in the center. This type of zoning is consistent with a previously proposed petrogenetic model. The comparison of the Saruhan granites with a classic example of paramagnetic granites reveals two contrasted FeO t –K m trends. This suggests that these variations can be a useful tool to distinguish between leucocratic paramagnetic and leucocratic ferrimagnetic granites.