Using methods of rock magnetism, the paper considers the possibility of understanding the physicochemical processes of rocks formation. The case study is the volcanic rocks drilled by the superdeep Saatly well. Within the interval of 3540-8126 m the composition of volcanic rocks varied with depth from basalts, andesite-basalts to dacites and rhyodacites. In rocks, magnetic minerals (iron and titanium oxides, iron sulfides, iron hydroxides and others) are sensitive to the conditions of their formation and consequent existence. This sensitivity to the physicochemical conditions of formation (as well as to the conditions of consequent existence) is reflected by the composition and degree of crystallization of magnetic grains. As a result of the study of the magnetic properties of volcanogenic rocks it was revealed that metamorphism (realized at depths of 3540-7000 m and mainly 5500-7000 m) leads to the crystallization of secondary fine magnetite grains carrying chemical remanent magnetization. Despite the intensive development of metamorphism, the system remains thermodynamically “conserved” at depths of 3540-7000 m. The processes of low-temperature metasomatism developing at depths of 7000-8126 m led to a decrease in the concentration of ferrimagnetic minerals in the rocks. Chemical residual magnetization becomes rarer and this occurs when oxidized magnetite is found. In some cases the generations of secondary hematite and pyrite were detected. Such change in the composition, concentration and characteristics of the natural magnetic state can occur in the thermodynamically “disclosed” system.

 

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