Synkinematic intrusions of the framing of the Zagan metamorphic core complexes (Southwestern Transbaikalia): Geochemistry and petrogenesis

The existence of a spatial-temporal relationship between the formation of m etamorphic-core complexes of Cordilleran type and syntectonic plutonic acti vity is shown by the example of the Zagan complex. Among tectonites of the framing of the Zagan complex we have recognized and studied thin tabular in trusive bodies of acid composition, whose position Is controlled by the zon e of major stripping. Their synkinematic origin is substantiated by geologi cal and structural data. Mobility of major and trace elements during dynamo metamorphic transformations is estimated for some intrusive bodies. The studied intrusive bodies are divided into two groups according to petro chemical composition: granites of the Zagan group of sills in the northern framing of the complex and leucogranite-pegmatites on the southern flank of the structure. The rocks of the first group have high contents of Ba (to 1 600 ppm), moderate concentrations of Sr and Zr, low contents of Y and, ofte n, Th and U, and fractionated REE patterns ((La/Yb)(n) - 13-25). These rock s might have formed under a high heat flow, typical of the initial stages o f development of metamorphic-core complexes. A distinctive feature of the s econd group of rocks is an extremely low content of LREE (La-n < 15) relate d to fractionation of minerals enriched in cerium rare earths during the ev olution of melt source. Fluids are shown to have actively participated in t he petrogenesis of these rocks.