ИСТИНА

Paleomagnetic studies are based on an analysis of the primary, or thermo-resistant, magnetization of rocks. The problem of separating the thermic and chemical components of magnetization has not been solved yet. An erroneous interpretation of the nature of magnetization can significantly affect the results of determining the paleointensity. In this work, samples of basalts from the rift zone of the Red Sea, with an average content of ulvospinel of 52 % and a Curie temperature of 260 °C, were annealed during 4.5–110 hours, at a temperature of 350 °C. Then SEM, TEM and XRD studies were conducted on the obtained states to determine the structure and changes in the elemental composition in grains of titanomagnetite. It has been established that with an increase in the annealing time up to 110 hours, the lattice parameter decreases from 8.455 Å to 8.417 Å. At the same time, the Curie temperature rises from 260 °C to 490 °C. This behavior is typical for single-phase oxidation. Deviations from the cubic structure were found in the sample with the maximum annealing time. The sample with the longest annealing time was then held in an atmosphere of pure argon (99.99%) for 40 minutes at 610 °C. After this exposure, TEM showed an increase in the lattice parameter to the initial value and a return to the cubic structure. At the same time the Curie temperature fell from 490 °C to 265 °C. On the investigated grains of titanomagnetite less than 10 micrometers in size, TEM and STEM showed no structural or elemental inhomogeneities, which also indicates a single-phase oxidation process. The results of the work show that annealing basalts in air at a temperature of 350 °C leads to a singlephase oxidation of titanomagnetite. Subsequent heating to 610 °C in argon atmosphere promotes its reduction. This work was supported by the RFBR (project № 16-05-00144).