Detrital zircon record of the early Paleozoic meta-sedimentary rocks in Russian Altai: Implications on their provenance and the tectonic nature of the Altai–Mongolian terrane

Abstract

An integrated U–Pb and Hf-isotope study on detrital zircons from the early Paleozoic meta-sedimentary rocks along the Charysh–Terekta–Ulagan–Sayan suture zone in Russian Altai was conducted in order to trace their provenance and tectonic setting. Most of the zircons possess oscillatory zoning and high Th/U ratios (>0.1), indicating their magmatic origin. The investigated samples yield similar zircon populations, i.e., dominant groups with late Neoproterozoic to early Paleozoic ages, followed by those from Mesoproterozoic to late Neoproterozoic and minor ones from Archean to middle Mesoproterozoic, indicating multiple tectono-thermal events in the source area. Comparison with surrounding tectonic units shows that the Tuva–Mongolian terrane and its adjacent island arcs possibly provided substantial materials to the sedimentary basin. These rocks show detrital zircon age patterns and Hf-isotope compositions similar to their counterparts in the Chinese Altai and Tseel terrane in western Mongolia, but different from those in the Gorny Altai terrane. Therefore, the investigated meta-sedimentary units possibly represented the northernmost segment of the Altai–Mongolian terrane. With combination of previous studies in the Chinese Altai and Tseel terrane, our data suggest that the Altai–Mongolian terrane possibly represents a coherent continental arc-accretionary prism system built upon the active margin of the western Mongolia during the Cambrian to Ordovician and thus does not support the micro-continent model with a passive margin.A compilation of U–Pb and Hf-isotope data of detrital zircons from the whole Altai–Mongolian terrane shows that the source area (i.e., the western Mongolia) underwent two most extensive magmatic activities at ca. 1.02–0.67Ga and 0.67–0.43Ga. These zircons possess both positive and negative εHf(t) values, suggesting significant crustal growth and reworking during the magmatic activities. Our study underlines a crucial role of Precambrian micro-continents (e.g., the Tuva–Mongolian terrane) and island arcs surrounding them in the formation of the Central Asian Orogenic Belt.