МОДЕЛЬ ГЛУБИННОГО СТРОЕНИЯ ЮЖНОЙ КАМЧАТКИ ПО РЕЗУЛЬТАТАМ ПЛОТНОСТНОГО 3D-МОДЕЛИРОВАНИЯ И КОМПЛЕКСУ ГЕОЛОГО-ГЕОФИЗИЧЕСКИХ ДАННЫХ

Abstract

In the south of Kamchatka, a number of deep geophysical studies have been conducted along the profile lines. The aim of the research was to study the lithosphere in the zone of present-day volcanism and active seismicity. Geological and geophysical models of the Earth's crust and upper mantle were constructed along the profiles. The results were obtained as part of two-dimensional modeling of geophysical fields. But the analysis of materials shows that the territory is characterized by a complex geological structure, which is reflected in three-dimensional distribution of gravitating masses. For the first time, the article presents the results of volumetric density modeling covering the territory of southern Kamchatka, including areas covered by the Sea of Okhotsk and the Pacific Ocean. The model is based on the technology of three-dimensional imaging of 2D modeling results obtained along the grid of intersecting profiles. The 3D modeling generated isodensity surfaces that enclose regions with layers of high density (≥ 3.33 g/cm3). Thus, the surface identified beneath the ocean is interpreted as a fragment of the top of the subducting plate and the surface under the peninsula is identified as the top of the paleosubduction zone. A subhorizontal high-gradient zone (3.0–3.3 g/cm3) is recognized in the density structures that intersect the 3D model, which is identified with the Moho boundary. A model of subduction interaction between oceanic and continental lithospheric plates is proposed. The two-dimensional model shows the formation of a transitional layer between the Moho boundary of the overhanging lithospheric plate and the top of the paleosubduction zone. In the transition layer, a low-density zone is distinguished, where individual areas of maximum low-density are associated with melting chambers. Conditions are shown for the formation of the crust block with abundant basic-ultrabasic intrusions and the diorite-granodiorite intrusive massif. All ore occurrences and gold deposits of the Karymshinsky ore cluster are located within the contours of projection onto the ground surface of the deep high-gradient zone that encloses the low-density zone. Ore occurrences are genetically related to the zones of crustal weakness where epithermal deposits are formed in closed hydrothermal systems. Based on the analogy, it is possible to prognosticate gold occurrences in other areas of the projection of the high-gradient zone.