GEODYNAMICS

Abstract

The purpose of the study. It needs to substantiate that sources of magnetic anomalies with wavelengths of the first thousand kilometers detected at the present time might have a magneto-mineralogical origin due to the existence of magnetic minerals at the mantle depths, in particular magnetite, hematite, native iron, as well as iron alloys. It should be also shown that present temporal changes of long-wave magnetic anomalies should be induced by changes of the magnetic properties of these minerals due to thermodynamic and fluid modes. According to numerous authors, the transformations of magnetic minerals occur in special tectonic zones of the upper mantle of the Earth, in particular at junction zones of lithospheric plates of different types, rifts, plumes, tectonic-thermal activation, etc. Areas of the upper mantle with temperatures below the Curie temperature of magnetite can be magnetic, such as subduction zones, cratons, and regions with the old oceanic lithosphere. Iron oxides might be a potential source of magnetic anomalies of the upper mantle besides magnetite and native iron, in particular hematite (α-Fe2O3), which is the dominant oxide in subduction zones at depths of 300 to 600 km. It was proved experimentally by foreign researchers that in cold subduction slabs, hematite remains its magnetic properties up to the mantle transition zone (approximately 410-600 km). Conclusions. A review of previous studies of native and foreign authors has made it possible to substantiate the possibility of the existence of magnetized rocks at the mantle depths, including native iron at the magneto-mineralogical level, and their possible changes due to thermodynamic factors and fluid regime. It has been experimentally proven by foreign researchers that in subduction zones of the lithospheric slabs their magnetization might be preserved for a long time at the mantle depths, as well as increase of magnetic susceptibility may observed due to the Hopkinson effect near the Curie temperature of magnetic minerals. Practical value. Information about the ability of the mantle to contain magnetic minerals and to have a residual magnetization up to the depths of the transition zone was obtained. It should be used in the interpretation of both modern magnetic anomalies and paleomagnetic data.