MINERALOGY, SOURCES AND AGE OF QUARTZITES OF THE OLKHON TERRAIN OF THE CENTRAL ASIAN FOLD BELT
S.I. Shkolnik1, 2, V.A. Makrygina3, E.A. Gladkochub1, E.A. Khromova2
1Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
2Dobretsov Geological Institute, Siberian Branch of the Russian Academy of Sciences, Ulan-Ude, Russia
3Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: Olkhon metamorphic terrane, quartzites, zircon, Cr-V mineralization, U-Pb age, condition of formation
Abstract
The article presents new data on a complex study of the composition of quartzites and gneisses of the Olkhon terrane. It has been established that the quartzites are typical metasedimentary rocks characterized by Cr–V mineralization—derived from volcanic exhalations—that is unevenly distributed throughout the stratigraphic section. The presence of organic matter in the sedimentary basin facilitated the precipitation of vanadium and chromium, as well as their subsequent sorption by clayey-organic material. The presence of quartzites with Cr-V and manganese mineralization in a single section may indicate alternation of oxidizing and reducing conditions in the sedimentation basin and the active tectonic regime during precipitation accumulation.
The morphological features of zircon from quartzite and its rare element composition suggest its age ~516 Ma as a result of a tectonothermal event, which contributed to the recrystallization of siliceous sediments with the formation of Cr-V mineralization (garnets, mica-roscoelites, chromium-vanadium oxides). The youngest population of detrital zircon from a biotite gneiss sample is 538 Ma, indicating that the sedimentary sequence formed within a narrow time of 538-516 Ma.
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