The Deep Structure Model for Southern Kamchatka Based on 3D Density Modeling and Geological and Geophysical Data.

Comprehensive deep geophysical studies were conducted along the profile lines in the south of Kamchatka. 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 crust and upper mantle were constructed along the profiles. The results were obtained as part of two-dimensional modeling of the geophysical fields. However, the data analysis shows that the territory is characterized by a complex geological structure, which is shown by the three-dimensional distribution of gravitating masses. This article presents the results of volumetric density modeling carried out for the area of southern Kamchatka, including the Sea of Okhotsk and the Pacific water areas, for the first time. The model is based on the technique of three-dimensional imaging of 2D-modeling results obtained from the network of intersecting profiles. The 3D modeling has revealed the isodensity surfaces that border layers of high density (≥3.33 g/cm3). Thus, the surface revealed beneath the oceanic water area 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 slab. A subhorizontal high-gradient zone (3.0–3.3 g/cm3) is recognized on the density sections that intersect the 3D model, which is identified as the Moho boundary. A model of the subduction interaction between the oceanic and continental lithospheric plates is proposed. A two-dimensional model shows the formation of a transitional layer between the Moho boundary of the overhanging lithospheric plate and the top of the paleosubducting oceanic plate. A low-density zone is distinguished in the transitional layer, where separate maximally low-density areas are identified as melting chambers. The conditions are shown for the formation of the crustal block, with abundant basic–ultrabasic intrusions and the diorite–granodiorite intrusive massif. All ore occurrences and a gold deposit of the Karymshinsky Ore Cluster are located within the contours of the projection onto the surface of the deep high-gradient zone that borders a low-density zone. Ore occurrences are genetically related to the zones of crustal weakness where the epithermal deposits are formed in closed hydrothermal systems. By analogy, it is possible to forecast gold ore occurrences in other areas of the projection of the high-gradient zone. [ABSTRACT FROM AUTHOR]