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Russian Geology and Geophysics

2019 year, number 4

A MODEL OF NONUNIFORM EXHUMATION OF KEYBOARD-LIKE STRUCTURES AS A POSSIBLE CAUSE OF METALLOGENIC BELT ZONING IN FOLDED AREAS

I.N. Kigai
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, 119017, Moscow, Russia
Keywords: Metallogenic belts, terranes, folding, orogeny, tectonometallogenic cycles, ore-magmatic stages and levels, keyboard-like structures of folded areas, nonuniform exhumation, ore-magmatic assemblages, ore zoning

Abstract

A metallogenic belt zoning is observed in folded areas of all metallogenic epochs from Precambrian to Cenozoic. The changes observed across the strike of folded areas on geological mapping are usually treated as geodynamic, petrologic/metallogenic, or temporal specialization of corresponding belts (terranes) and zones. However, there are serious petrological reasons to expect a significant downward change in the basicity of igneous rocks and the composition of related mineralization in folded areas. The change may be caused both by the relationship between the densities of magmas and country rocks and by the relationship between the solidus temperatures of different magmas and the thermal gradient pattern on the path of magma ascent. More basic igneous rocks and related mineralization should be detained at deeper levels of the lithosphere because of the higher density and higher solidus temperature of magmas. During the orogeny, the vertical differential movements of several adjacent terranes located between deep-seated faults can create some keyboard-like structures composed of parallel belts variously uplifted and subsided, similarly to white and black keys of a piano. In more uplifted and then more denuded belts and blocks of such structures, the ore-magmatic complexes earlier located at deeper levels can be exposed at the surface. As a result, a metallogenic belt zoning can be generated, which can be absolutely of no (or only partial) relation to any prefolding primary sedimentary or other material or temporal specific features of terranes. The possibility of such nature of metallogenic belt zoning is shown here with the use of geophysical data for two important ore-producing regions of Russia: eastern Transbaikalia and southern Primorye. The model is proposed as one of the possible ways of formation of metallogenic belt zoning in some other folded areas. This research work will probably favor a more profound analysis of the nature of metallogenic belt zoning in the considered and other regions of the world with the application of modern geophysical methods. The use of the described regularities of the stage arrangement of igneous rocks of different basicity and oxidation state and genetically related hydrothermal ores can facilitate prospecting for ores of different metals and their 3D forecasting in keyboard-like structures of Phanerozoic orogens and ancient platforms.

DOI: 10.15372/RGG2019030