Granodiorites in Tuff Conglomerate Boulders of the Cambrian Shurmak Formation: Evidence of Continental Neoproterozoic Magmatism in the South of the Tuva Segment of the Central Asian Folded Belt

A geochemical study and geochronological justification of the age of granitoids from the clastic components of tuff conglomerates of the Shurmak Formation in southern Tuva are performed. They have uniform composition and correspond to low-alkaline granodiorites, are characterized by enrichment in light REEs, Zr, Th, Hf and manifested minima in Eu, Nb, P, and Ti. U–Pb dating by the LA-CIP-MS method of zircons from three granite boulders has determined their ages as 784 ± 2, 785 ± 2, and 773 ± 2. All studied samples contain xenogenic zircons with ages of 1018, 1807, 1897, 1982, 1984, and 2085 Ma, which is consistent with the Sm–Nd isotopic data for these rocks, Т(DM2st) age of 1.85 Ga, εNd(t) = ‒3.4. This suggests that they formed from a late Paleoproterozoic crustal source. At present, the existence of Neoproterozoic granitoids within the Tuva segment of the Central Asian folded belt has not been established.