Abstract—This article describes the geological structure of the Sarsangi gabbro–diorite–plagiogranite complex located in the boundary zone between the Middle and South Urals. The formation of its massifs took place in the Late Silurian in the abyssal zone at approximately 6.5–7.0 km. The temperature ranges of crystallization of granodiorites and gabbro were 900–990°С and 1180–1280°С, respectively. The pressure in the system at that time was 190–200 MPa. Gabbroids in the massifs were formed under conditions of extension of the oceanic crust. In terms of petrogeochemistry, they correspond to rocks that compose the basement of island arcs and belong to the ophiolite formation.