Sm‒Nd Age of Sviatonossites of the Svyatoi Nos Peninsula (Eastern Baikal Region)

Sviatonossites are syenites with andradite garnet, a rare type of igneous rocks described by P. Eskola in 1913 on the Svyatoi Nos Peninsula (Lake Baikal). Due to the absence of zircon in the rocks, which makes it possible to date them reliably by the U‒Pb method, geochronological Sm–Nd studies of the bulk composition and minerals are carried out. As a result, two estimated periods of the formation of sviatonossites are obtained. According to the bulk composition and four minerals (garnet, pyroxene, potassium feldspar, and apatite), the age is 262 ± 21 Ma (RMSD = 1.6), and according to the bulk composition and garnet, it is 274 ± 25 Ma (RMSD = 0). The results obtained coincide with the timing of tectonic–metamorphic and igneous processes associated with the formation of the Eastern Transbaikalia segment of the Central Asian (Mongol–Okhotsk) folded belt. Sviatonossites in the complexes of mobile (folded) belts framed by the Siberian Craton are indicator rocks reflecting the manifestation of mantle–crustal interaction.