Age of the Ust’-Gilyui sequence in the Stanovoi Complex of the Selenga-Stanovoi Superterrain, Central Asian fold belt

Abstract

According to the results of U-Pb geochronological investigations, the age of the amphibolite protoliths (metabasalts) in the Ust’-Gilyui sequence within the Stanovoi Complex of the Amazar-Gilyui structural and formational zone in the Selenga-Stanovoi Superterrain of the Central Asian fold belt can be estimated at 193 ± 1 Ma. The Nd model age of the Ust’-Gilyui metasedimentary rocks is in the interval of tNd(DM) = 1.1–3.1 Ga. This information along with the previously obtained geochronological data are indicative of the fact that the Ust’-Gilyui sequence consists of metasedimentary and metavolcanic rocks of various ages: (1) volcanic rocks with the age of 193 ± 1 Ma; (2) metasedimentary and metavolcanic rocks broken through by the Paleozoic granitoids dated to 370 Ma and characterized by minimum estimations of tNd(DM) = 1.1 Ga, i.e., rocks with an age of 1.1–0.4 Ga. In addition, it is quite possible that this sequence also includes more ancient rocks. The SSS Amazar-Gilyui structural and formational zone is likely to be a tectonic melange composed of the metasedimentary and metavolcanic rocks of the Mesozoic and, probably, Paleozoic and Early Precambrian ages. The studied zone was formed in the Mesozoic, most likely, in the course of the collision processes initiated by the closing up of the Mongol-Okhotsk Ocean.