ИСТИНА

The magnetic properties and mineralogy of titanomagnetite in the pillow basalt of the Red Sea of Holocene age at different distances (0-7 cm) from the contact surface with water were studied. It was revealed that the composition of titanomagnetite in the pillow basalt changes from the crust deep into the pillow: the titanium content in titanomagnetite increases, while the magnesium and aluminum content decreases. Titanomagnetite in the surface layer of pillow basalt (0-2 cm) is single-phase oxidized, with a maximum oxidation degree of 0.13, and at a distance of more than 3 cm from the crust has a stoichiometric composition. Electron and magnetic force microscopy observations show that the concentration of titanomagnetite in basalt and the size of titanomagnetite crystals increase with distance from the crust, and the domain state changes from single-domain to pseudo-single-domain. These changes lead to an increase in magnetic susceptibility (0.2 to 1.8 10-2 SI), saturation magnetization from (0.026 to 0.895 A·m2/kg) and residual saturation magnetization (0.014 to 0.296 A·m2/kg), and a decrease in coercivity (Hc from 90 to 15 mT, Hcr from 153 to 20 mT). It was found that the coercivity of titanomagnetite grains correlates with the maximum cooling rate of basalt. The NRM of basalt varies non-monotonically with distance from the surface of contact with water: up to a depth of about 3 cm its growth caused by the growth of titanomagnetite concentration is revealed, further reduction caused by the increase in the size of titanomagnetite crystals. Despite the variation in the structure, composition of titanomagnetite, and magnetic properties of pillow basalt at different distances from the quenched crust, experiments by the Tellier-Coe method in argon showed close values of the geomagnetic field paleointensities (62.5-66.0 μT). This work was supported by the Russian Foundation for Basic Research, grant 20-05-00573.