Submicroscopic texture in titanomagnetite grains in basalt studied using the torque magnetometer and electron microscope

Abstract

Samples of basalt containing homogeneous titanomagnetite have been subjected to heat treatment in air, in the laboratory, under conditions which produce multiphase oxidation products. The evolution of the microstructure in the titanomagnetite was monitored using the electron microscope and by measuring the rotational-hysteresis characteristics of the samples. This latter technique proves to be very sensitive to small changes which are undetectable by the optical or electron microscopes. Rotational-hysteresis curves and coercivity spectra, derived from acquisition of IRM and AF demagnetization of IRM, all indicate an appreciable fraction of coercivities in excess of 1 kOe in optically homogeneous (Class I) titanomagnetitie with submicroscopic microstructure. It is possible to divide Class I of the petrological scale into three or four subclasses. Class-I basalts may be assigned to the subclasses on the basis of the effect of slight laboratory heating on the rotational-hysteresis characteristic.