Early Triassic Monzonite–Granite Series in Eastern Kazakhstan as a Reflection of Siberian Large Igneous Province Activity

Abstract

We provide the results of studying the internal structure and composition of the rocks of the Semeitau and Delbegetei massifs located in Eastern Kazakhstan. It was previously believed that these massifs have different ages and were formed in different geodynamic settings. The U-Pb zircon age from the monzonites and quartz monzonites was determined to be 249 ± 2 Ma, which showed the same Early Triassic age of the massifs. Both massifs are composed of rocks of the same monzonite–granite series of rocks with a significant proportion of high-silica rocks (leucocratic granites). Intermediate rocks are formed due to the differentiation of subalkaline mafic magmas, and the felsic rocks (rhyolites and granites) are the result of partial melting of crustal substrates. The massif formation model assumes the intrusion of mafic magmas into the crust, their differentiation and mixing with crustal melts, and then the intrusion of various rocks into the upper crustal levels. Analysis of the geological position, age and composition of the rocks allows us to conclude that the Semeitau and Delbegetei massifs were formed in an intraplate geodynamic setting. The activity of the mantle plume is the most probable reason for their formation. The Semeitau and Delbegetei massifs can be included in the southern part of the range of the Early Triassic Siberian Large Igneous Province.