| Abstract: | The central portion of the Aldan Shield hosts very widely spread Archean and Early Proterozoic granitoids, much of which are
granite-gneisses. Geochemical lines of evidence, data on inclusions in minerals, and Sm-Nd isotopic geochemical data suggest
that the protoliths of granite-gneisses in the central part of the Aldan Shield were granitoids that had various composition,
age, and were derived from distinct sources and under different parameters and were then emplaced in different geodynamic
environments. The granitoids belong to at least two types of different composition that occur within spatially separated areas.
The protoliths of granite-gneisses in the western part of the Western Aldan Megablock and the junction zone of the Chara-Olekma
and Aldan geoblocks (granite-gneisses of type I) had the same age and affiliated to the same associations as the within-plate
granitoids of the Nelyukinskii Complex. Their parental melts were derived at 2.4–2.5 Ga by the melting of Archean tonalite-trondhjemite
orthogneisses of the Olekma and Aldan complexes. The protolith of granite-gneisses in the eastern portion of the Western Aldan
Megablock (granite-gneisses of type II) can be subdivided into two groups according to their composition: granitoids with
geochemical characteristics of subduction- and collision-related rocks. The protoliths of the type-II granite-gneisses with
geochemical characteristics of subduction granitoids were produced simultaneously with the development of the Fedorovskaya
island arc (at 2003–2013 Ma), whereas the protoliths of the type-II granite-gneisses with geochemical characteristics of collision
granitoids were formed in the course of accretion of the Fedorovskaya island arc and the Olekma-Aldan continental microplate
at 1962–2003 Ma, via the melting of magmatic rocks of the Fedorovskaya unit and older continental crustal material. |
