Origin and structural position of the Kamchatka median massif according to deep geological and geophysical surveys

The article shows the results of deep research along the profile of the settlement of Nizhnyaya Oblukovina – the city of Andrianovka, crossing the northern part of the Kamchatka median massif. A geological and geophysical model of the structure of the earth’s crust and upper mantle has been constructed, where the structural position of the object under study is presented and an assumption is made about its origin. The model highlights a fragment of paleosubduction (slab), which was part of the most ancient convergent boundary in western Kamchatka. The final stage of subduction blocking and its displacement to the east at a distance of ~60 km in the Early Eocene is associated with the entry into the accretionary complex of a terrane in the form of an island-arc plate 6–9 km thick. At the site of the maximum inflection of the subsequent slab, an extension zone was formed – a rift zone, along which the rise of mantle material and high-temperature fluid occurred. Approximately 52 million years ago, the processes of metamorphism, focal melting and intrusion of granites into the upper layers of the crust took place. As a result, in the eastern part of the plate and its flanks, a granitoid massif was formed with a rock density of 2.58 g/cm3, which is significantly lower than the environmental density. Density deficiency led to a violation of isostatic equilibrium and, as a result, to a rise in this part of the structure. The most intense uplift occurred at the end of the Oligocene, as a result of which a ledge was formed, which the authors recommend giving the name: “Middle Kamchatka ledge” instead of the rooted “Kamchatsky median massif”. The genetic relationship of the Shanuch ore region with the features of the deep structure of the lithosphere has been revealed. The results of the research indicate a hidden (buried) distribution of the island-arc plate beyond the boundaries of the mapped outcrops of metamorphids. Intrusions of the main composition, promising for the opening of sulfide copper-nickel ores, are located in the marginal parts of the ledge.