Seperation of ferromagnetic and paramagnetic anisotropies of igneous rocks by using High-Field Analysis (HFA): case study of Malayer igneous rocks

The magnetic anisotropy of rocks results from the contributions of diamagnetic، paramagnetic، & ferromagnetic minerals. This bulk anisotropy of magnetic susceptibility، which can be rapidly measured with modern instruments، generally provides a better understanding of the rock deformation history. Different minerals in a rock can form at different times and also respond to deformation in different manners. Therefore it is useful to separate their respective contributions to the whole rock magnetic fabric. Various techniques available to achieve this separation among them measurement of the magnetic properties at high fields، above the saturation magnetization of ferromagnetic minerals، effectively separates the diamagnetic-paramagnetic magnetic anisotropy. In this paper، the anisotropies of ferromagnetic and paramagnetic components are separated using High-Field Analysis torque for 37 samples of natural rocks. These samples are igneous rocks of Malayer that are mainly composed of paramagnetic minerals (e. g. biotite and amphibole) and few portions of ferromagnetic minerals (e. g. titanomagnetite) which are located in the quratz-feldespathic (diamagnetic) context. Anisotropy of Magnetic Susceptibility (AMS) in low field analyses indicated that paramagnetic phases are the dominant control of the magnetic fabric. This is confirmed by High Field Analyses (HFA) which implied that magnetic characteristics are dominated by paramagnetic minerals، except for three samples.