AN ACTIVE NEOPROTEROZOIC CONTINENTAL MARGIN OF THE ZAVKHAN MICROCONTINENT (MONGOLIA): ISOTOPIC-GEOCHRONOLOGICAL EVIDENCE

There have been presented the results of study a thick (no less than 2–3 km), extended (for more 200 km) volcanogenic formation (Tsetsen-Uul or Yargait) in south Zavkhan terrane Central Asian fold belt. The is an assemblage frequently intercalating effusive rocks subalkaline basalt-andesite-dacite-rhyolite series, their tuffs, tuffites, ignimbrites, and terrigenous rocks. Felsic dominate over basites, tuffogenic effusives. some evidence that emerged subaerial setting, with explosive eruptions, petrogeochemical features are typical for subduction environment. felsic high negative ε Nd from –11.5 to –12.8 Early Precambrian model age T (DM)=2.4–2.5 Ga, which indicates presence ancient crust at depth its involvement magma. supports volcanic within active continental margin. continental-margin stage ranges ~860 Ma ~780 based on LA-ICP-MS U-Pb dating zircons. Tsetsen-Uul (Yargait) similar structure composition Sarkhoi group Tuva-Mongolian massif, partially overlaps them time. It concluded all three formations same geodynamic setting time interval, fragments arc belonging both paleomicrocontinents.