Magnetic Granulometry of Killari Borehole Basalts

Laboratory investigations aimed at inferring the nature of magnetic grains (magnetic granulometry) are reported for nine basaltic flows with thicknesses between 15 and 75 meters encountered in a borehole drilled at the recent Latur earthquake site near Killari village in Latur district, Maharashtra. Five to eight samples were studied for saturation remanent hysteresis, low-field hysteresis, susceptibility variation with temperature and Lowrie-Fuller test, apart from the alternating field (AF) and thermal demagnetizations. Magnetite and titanomagnetite with coercive forces (Hc) in excess 15 mT in mixed domain states of single, multiple, cation-deficient and superparamagnetic grains are inferred to be responsible for remanence in these rocks. These rocks exhibit very stable behaviour during alternating field and thermal demagnetization studies with median destructive fields >20 mT and blocking temperatures between 400 and 580°C.