Petrogeochemical characteristics and U-Pb age of morion-granite rocks in Central Transbaikalia: Classification and genesis problems

Abstract

Research subject. This article presents data on the age, material composition, petrogenetical and geochemical properties of morion-containing granites in the Etytei and Khamnigadai massifs of Central Transbaikalia.Materials and methods. The composition of rock samples was investigated using the methods of chemical analysis, XRD and ICP-MS; the age was determined by the zircon U–Pb method using SHRIMP and LA-ICP-MS; the mineral composition was studied using an LEO-1430 electron microscope.Results. The massifs composed of morion-containing granites belong to Early Jurassic (190–185 Ma) and form the peripheral area of the Early Mesozoic Khentei-Dauria magmatic region.Conclusion. According to their petrochemical and mineralogical characteristics, the morion-containing granites under study differ from typical intra-plate granitoids and correspond to the “oxidized” A-type granites. The black smoky colour of quartz contained in granite samples is associated with a relatively high radioactivity of rocks caused by the presence of accessory thorium and uranium-containing minerals.

Keywords

• morion-granites
• leucogranites
• geochemistry
• geochronology
• central transbaikalia