COMPARATIVE CHARACTERISTICS OF THE MINERALOGICAL COMPOSITION OF OLD IRRIGATED SOILS OF NAVOI AND STEPPE SOILS OF THE KANIMEKH DISTRICT OF NAVOI REGION (UZBEKISTAN)

An isotopic-geochronological and geochemical study of zircon and fluorapatite was conducted on Paleoproterozoic granitoids from the Ros-Tikych Domain in the south-western part of the Ukrainian Shield. Granitoids of three age populations (ca. 3.8, 3.0-2.8, and 2.1-2.0 Ga) are widely distributed in the Middle Bouh area, which includes the southern part of the Ros-Tikych Domain. This study aimed to clarify the origin of the Paleoproterozoic granitoids. Using the U-Pb dating method, new data were obtained regarding the formation time of charnockitoids (so-called "sobites") in the Haisyn block. Zircon from two-pyroxene diorite yielded an upper intercept age of 2087±16 Ma (a single inherited crystal yielded an age of 3174±13 Ma). Fluorapatite from diorite and monzosyenite yielded a U-Pb age of 1451±110 Ma. The hafnium isotopic composition in zircon from two-pyroxene diorite has a negative weighted average εHf of –4.3±0.8. According to the felsic crust model (176Lu/177Hf = 0.010), the model age is ca. 2800 Ma; for the inherited crystal, it is ca. 3800 Ma. The oxygen isotope ratios (δ18OVSMOW values) in fluorapatite range from 5.1 to 6.1 ‰, with a mean value of 5.6±0.3 ‰ (1 standard deviation). This corresponds to the mantle values characteristic of tonalite-trondhjemite-granodiorite (TTG) associations. The data suggest that the Paleoproterozoic charnockitoids formed as a result of melting the Meso-Neoarchean lower continental crust. After crystallisation, these rocks underwent slow cooling and exhumation from 800-750 °С at ca. 2.1 Ga to 500-400 °С at ca. 1.4 Ga.