A. A. Mongush, F. P. Lesnov, Ch. K. Oydup, Ch. O. Kadyr-ool, S. A. Chupikova

Isotope and geochronological data on ultramafic and mafic complexes in Tuva (Central Asia) and zircon polychronism: A brief review

Abstract. The paper synthesizes published isotope and geochronological data on ultramafic and mafic complexes in Tuva, including ultramafite, gabbroid, chromitite, basalt volcanite, subvolcanite, and genetically related rocks. The review is based on published U-Pb zircon data (obtained with LA-ICP-MS, SIMS/SHRIMP, and ID-TIMS), as well as 40Ar/39Ar and K–Ar ages. Their interpretation adds to analyzing the morphological, microtextural, geochemical, and isotope criteria to discriminate between different genetic zircon types. The available geochronological dataset for Tuva spans the interval from the Precambrian to the Paleogene–Quaternary and defines three principal age groupings: Vendian–Ordovician, Devonian–Permian, and Paleogene–Quaternary. The former is the most prominent one. Zircon polychronism in mafic-ultramafic rocks in Tuva proves to be a persistent regional feature and, in most cases, corresponds to zircon populations rather than individual crystals. The results further demonstrate that the U–Pb age of zircon from zircon-poor mafic and ultramafic rocks cannot automatically match the host rock crystallization age. Robust interpretation requires differentiation between igneous, inherited, xenogenic, and overprinted zircon within an integrated petrochronological framework and comparison with independent geochronometers.

Keywords: U–Pb zircon dating, genetic types of zircon, geochronometry, Ar/Ar dating