Metamorphism of the Uni Suite as an Indicator of Early Precambrian Collisional Processes in the Vyatka Belt, Northeast of Volgo–Uralia

Abstract

According to the core data from two deep holes, the following mineral assemblages were identified in metapelitic rocks of the Uni Suite in the central part of the Vyatka Belt, sandwiched between Archean blocks in the northeastern part of the Volgo–Uralian Segment of the East European Craton: (1) Pl + Ms + Bt + Qz + Kfs + And ± Chl and (2) Pl + Bt + Qz + Kfs + Grt + Sil ± Ms ± Chl. A set of methods including classical (Grt–Bt, GASP, Ti-in-Bt, and Ms–Bt) and multi-equilibrium thermobarometry (winTWQ 2.34), as well as the isopleth intersection method on pseudosection diagrams (GeoPS 3.2.2.128), was applied to estimate the P–T conditions for these assemblages. The calculated P–T parameters of metamorphism are 520–650°C (or up to 690°C, according to the isopleth method) and 2–5.4 kbar. Metamorphism of paragneiss containing assemblage (2) was accompanied by anatexis in the water-saturated system. Metamorphism of rocks of the Uni Suite belongs to the relatively shallow type of the andalusite–sillimanite facies series and amphibolite facies and relates to deformations during orogenes.