A Model of Keyboard-Like Nonuniform Exhumation as a Possible Cause Zoning of Metallogenic Belts in Folded Areas (Eastern Transbaikalia and Southern Primorye)

Abstract

Abstract —Zoning of metallogenic belts 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, petrometallogenic, 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 magmatites and the composition of related mineralization in folded areas. The change may be caused both by relationships between the densities of magmas and country rocks and by relationships between the solidus temperatures of different magmas and the thermal gradient pattern on the magma ascent path. More basic magmatites and related mineralization should be detained at the deeper levels of the lithosphere because of the higher density and higher solidus temperature of magmas. During orogeny, the vertical differential movements of several adjacent terranes located between deep-seated faults can create keyboard-like structures composed of parallel belts variously uplifted and subsided, similarly to white and black keys of a piano. In belts and blocks of such structures more uplifted and then more subjected to denudation, the ore-magmatic complexes earlier located at deeper levels can expose at the surface. As a result, zoning of metallogenic belts can form, which is totally or only partly related to the metallogenic specialization of structure-facies zones and terranes. The possibility of this origin of zoning of metallogenic belts is shown with the use of geophysical data for two important ore-producing regions of Russia — eastern Transbaikalia and southeastern Primorye. The above model is proposed as one of the possible ways of metallogenic-belt formation in some other folded areas. The author hopes that this work will stimulate a more profound analysis of the nature of metallogenic-belt zoning in the considered and other world regions with the use of modern geophysical methods. The use of the described regularities of the storied arrangement of magmatites of different basicity and oxidation states and genetically related hydrothermal ores may facilitate prospecting for ores of different metals and their 3D forecasting in keyboard-like structures of Phanerozoic orogens and ancient platforms.