THE EVOLUTION OF THE CHEMICAL AND MINERAL COMPOSITIONS OF MESOZOIC AND CENOZOIC SILTY-SANDY ROCKS ALONG A TECTONIC PROFILE FROM THE RUSSIAN PLATFORM TO THE CAUCASUS GEOSYNCLINAL REGION

Abstract

The distribution of rock-forming and accessory minerals, major and trace elements in silty-sandy rocks along the tectonic profile was estimated from analyses of composite samples made up of 14000 individual samples, systematically collected from the Russian and Scythian platforms, foredeeps in the Fore-Caucasus, mio- and mesogeosynclines of the Greater Caucasus, Transcaucasian Median Mass, Rioni-Kura Intermontane Trough, eugeosyncline of the Lesser Caucasus, and Aras Intermontane Trough. A systematic increase in the plagioclase content and the Al, Fe, Mg, Na, Cu, Co, and Zn concentrations toward the inner geosynclinal zones was detected. The iron oxidation state attains a maximum at the ends of the tectonic profile, while the highest degree of iron reduction is related to the mesogeosyncline of the Greater Caucasus, Abrupt breaks in the zircon/magnetite and K/Rb trends at the miogeosyncline/median mass/eugeosyncline boundaries mark the replacement of material derived from the ancient continental crust by cruslal material from the young island arc. The variations in the chemical and mineral compositions of silty-sandy rocks along the tectonic profile are much more contrasting and systematic than the variations within particular zones during the Alpine cycle.