Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

The article presents the results of isotopic, geochronological, geochemical and mineralogical studies, as well as mineral composition analyses of melanocratic enclaves within the granites of the Sarkhoy complex (Kaakhem magmatic area, Eastern Tuva). According to geochronological data (zircon, U-Pb), the age of the enclaves differs from that of the host granites (480 MA and 450 MA, respectively). The εNd(T) values for the enclaves are +3.2, while for the Sarkhoy complex granites, εNd(T) ranges from 0.5 to 1.7. This suggests that the enclaves cannot be considered cumulates from an earlier phase of granite melt crystallization or restites of the Sarkhoy complex granitoid protolith. Melanocratic enclaves represent xenoliths that, based on their age and isotopic characteristics, can be attributed to the early phase of the diorite-tonalite-plagiogranite association of the Early Tannuola complex. Entrapment of fragments of mafic rocks occurred during the ascent of the granitic melt (~450 million years ago) at the middle crustal level (T ~ 700°C, P = 1.9–2.5 kbar), leading to their partial assimilation and compositional alteration through interaction with the felsic melt.The presence of xenogenic zircon in the Sarkhoy complex granites, with an age of 480 million years, comparable to the age of the xenoliths, suggests a possible contribution of Early Ordovician complexes to the formation of a significant volume of magmatic melt in later stages of regional evolution. Xenoliths of basic rocks in the granitoids of the Sarkhoy complex, studied in the eastern part of the Kaakhem area, represent products of melting of the primitive mantle, which fundamentally distinguishes them from the coeval gabbroic complexes of the western part of the area.