Nature secondary quartzites of the island Bol’shoy Tyuters (Gulf of the Finland, Russia)

Territory Baltic shield is well understood and the identification of innovative geological formations rare stroke of luck. Thanks to the Russian Geographical Society in the summer of 2015 an integrated expedition to study the nature of the little-known islands of the Outer Gulf of Finland was carried out and found, much quartz rocks (SiO₂ more than 90%) that compose most part of the island Bolhoy Tyuters. As a result of complex studies including petrogeochemical, microprobe, isotope, thermobarogeochemical investigations and chromatographic analysis of gases, it can be asserted that these rocks are secondary quartzites formed under the influence of carbon dioxide solutions. The presence of shadow structures of migmatites, as well as mineralogical features of quartzites, suggest that the initial rocks, on which secondary quartzites were formed, could be shales of the svecofennian complex. The temperature of homogenization of gas-liquid inclusions is 330-370°C, which indicates a high-temperature facies of secondary quartzites. The age of the dikes of the granite composition, which break through secondary quartzites, is close to 1660 and 1680 million years, which is somewhat older than the main phase of rapakivi granites (1650-1550 my) and coincides with the pre-Riphean weathering era, at the end of which the formation of the largest “type of disagreement” occurred. The formation of secondary quartzites of B. Tyuters, as well as for most classical manifestations of this type, we associate with the fluid-explosive activity of volcanoes preceded of rapakivi granites, whose products, in the form of basic and acidic lavas, were preserved as part of the Early Riphean strata located on the island Hogland. Considering the huge resources of these quartzites (more than 370 million tons), this manifestation is very promising for high purity quartz raw materials, close to the North-Western industrial area and St-Petersburg. The formation of a subhorizontal plane controlling the formation of a deposit of secondary quartzites and Early Riphean sediments and rapakivi granite intrusions, we associate with the tectonic activity of the marginal part of the Baltic Shield, known as the Polkanov lineament.

Финский залив, о. Большой Тютерс, вторичные кварциты, железоглиноземистые метасоматиты, граниты, вулканиты, сланцы, сброс, Gulf of Finland, Bol’shoy Tyuters, secondary quartzite, iron-alumina metasomatic rocks, granites, volcanic rocks, schist, fault

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