Metallogeny of subduction zones

The paper deals with the multistage mechanism of the Earth's crust enrichment in ore elements in underthrust zones. The processes of metamorphism and the formation of hydrothermal solutions at pulling of the watered oceanic lithospheric plate into the subduction zone have been described. Some physical and chemical transformation regularities of structural-material complexes in these areas and mechanisms of the formation of ore deposits have been discussed. Spatio-temporal patterns of the localization of a number of endogenetic and exogenetic deposits have been described using metallogeny of the Ural and the Verkhoyansk-Kolyma Fold Belts as an example. It has been shown that in nature there are several effective mechanisms of the enrichment of the crust in ore minerals. One of them is the process of pulling into subduction zone of metalliferous sediments and ferromanganese crusts as well as seabed nodules, their metamorphic transformation, partial melting and transition of ore components into magmatic melts and mineralized fluids. In the future this leads to the release of ore material by magmas and hydrothermal solutions into the folded formations of island-arc and Andean types and the formation of igneous, metasomatic and hydrothermal deposits. Another, yet no less powerful natural mechanism of a conveyor enrichment of the crust in ore elements is the process of destruction and sedimentation of mineral deposits formed in the folded areas as well as the formation of placers and their transfer to the marginal parts of the continent. Later, during the collision of active and passive margins of two lithospheric plates, such as the collision of the Kolyma Massif with the eastern part of the Siberian craton in the middle of the Mesozoic there was a thrusting of a younger lithospheric plate over a more ancient one. As a result, the sedimentary sequences of the passive margin of the Siberian plate were submerged and partially melted by the basic magmas intruded in the bottom of the cut. This led to the transition of a part of ore elements from placers to igneous rocks of granitoid composition and fluid solutions, thereby forming magmatic, metasomatic and hydrothermal mineral deposits. Cyclic enrichment of the Earth's crust in this way can repeatedly manifest itself in the history of the Earth and lead to the enrichment of ore deposits from the ancient complexes to the young ones. Studying processes of geodynamic evolution of the structural-material complexes of continental and oceanic lithosphere is important to understand the processes of ore genesis in the Earth's crust. Most endogenetic deposits are closely connected with the processes of metamorphism, magmatism and hydrothermal activity and are usually formed at the margins of lithospheric plates. A part of exogenetic deposits is also genetically connected with endogenetic and is formed due to their destruction. The regularities of ore genesis in underthrust zones described in the paper cover only a part of the natural processes of the Earth's crust enrichment in ore minerals. The paper has also focused on polycyclic and conveying mechanisms of the formation and transformation of ore elements in subduction zones, as well as on the mechanism of remobilization of ore-bearing deposits and their joint transfer to the upper structural layers of the folded system and the formation of ore-bearing volcano-plutonic associations.