This paper presents the results of 3D numerical thermomechanical modeling of formation processes of the Precambrian Posolnenskiy granitoid massif located within the Angara-Kansk block of the South Yenisey Ridge. Geological and geochronological data (U-Pb and 40Ar/39Ar) indicate the polychronous nature of the massif, including both ancient (~1.8 Ga) granitoids and younger (~500 Ma) subalkaline granites and syenites. Based on an analysis of structural-geological and geochemical features, two main stages have been identified in the massif’s evolution. The first stage is associated with the formation of autochthonous granitoids due to dissipative heating under shear deformation conditions in the Posolnenskiy-Kuzeevskiy tectonic zone. Modeling showed that at shear rates of at least 2 cm/yr and at depths greater than 35 km, the energy dissipation could have led to localized melting of crustal material, facilitating the formation of granitic melts. The second stage is characterized by the intrusion of high temperature subalkaline magmas, the generation of which requires temperatures above 800 °C, unattainable through dissipative heating. Consequently, the likely primary heat source was mantle magmas injected during underplating. Thus, the formation of the Posolnenskiy Massif is explained by a combination of crustal processes driven by viscous deformations and mantle thermal influence, emphasizing the multifactorial nature of granitoid magmatism in collisional belts.