PETROGENESIS OF MELANOCRATIC ENCLAVES OF IGNEOUS ROCKS IN THE SARKHOI COMPLEX GRANITOIDS (<i>Kaa-Khem magmatic area, Eastern Tuva</i>)

We present the results of isotope, geochronological, geochemical, and mineralogical studies and mineral composition analyses of melanocratic enclaves in the granites of the Sarkhoi Complex (Kaa-Khem magmatic area, Eastern Tuva). According to geochronological data (zircon U–Pb dating), the age of the enclaves differs from that of the host granites (480 and 450 Ma, respectively). The εNd(T) values for the enclaves are 3.2, while for the Sarkhoi Complex granites, they range from 0.5 to 1.7. Therefore, the enclaves cannot be considered cumulates from the earlier phase of granite melt crystallization or restites of the Sarkhoi Complex granitoid protolith. Melanocratic enclaves are xenoliths, which, based on their age and isotope characteristics, can be attributed to the early phase of the diorite–tonalite–plagiogranite association of the Early Tannu-Ola Complex. Fragments of mafic rocks were trapped during the ascent of granite melt (ca. 450 Ma) at the middle crustal level (T of ca. 700 °C, P = 1.9–2.5 kbar), which led to their partial assimilation and compositional alteration through interaction with felsic melt. The xenogenic zircon present in the Sarkhoi Complex granites has an age of 480 Ma close to the age of the xenoliths, which suggests the contribution of Early Ordovician complexes to the formation of a significant volume of magmatic melt at the later stages of regional evolution. Xenoliths of mafic rocks in the granitoids of the Sarkhoi Complex, studied in the eastern part of the Kaa-Khem area, are products of melting of the primitive mantle, thus fundamentally differing from the coeval gabbroid complexes in the western part of the area.