Tectonic Setting of Middle–Upper Cambrian Sediments of Bolshevik and Troynoy Islands (Russian Arctic): a Case of Detrital Rocks from Metaterrigeneous Complexesстатья
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Аннотация:The article presents new data on the tectonic setting and conditions for the formation of Middle–Upper Cambrian complexes in the southern part of the North Kara block, obtained from a study of clastic rocks from metaterrigenous basement complexes of Troynoy Island (Izvestia CEC archipelago) and the northern part of Bolshevik Island (Severnaya Zemlya archipelago). Metasandstones from both study areas have close compositions of lithic wackes and similar sets of rock fragments. Detrital zircons and Cr-spinels from sandstones of both regions have similar Zr/Hf and TiO2/Al2O3 ratios. The similarity of coeval sediments from both regions can be explained by their accumulation due to erosion of detrital material from a single source area, which was a segment of accretionary uplift of the Timan–Severnaya Zemlya orogenic belt, with newly formed continental Neoproterozoic–Cambrian crust. The structure of the source area was dominated by low- and medium-grade metamorphosed terrigenous complexes; volcanic and intrusive complexes were also present, attributed, based on the geochemical signatures of clastic Cr-spinels, to island-arc and back-arc ophiolite formations. By the beginning of the Ordovician, Middle–Late Cambrian sediments were also folded, metamorphosed, and integrated in the structure of the Timan–Severnaya Zemlya orogenic belt. The features of the petrographic composition, grain size distribution, and sorting of metasandstones from the north of Bolshevik Island are more characteristic of accumulated sediments resulting from gravitational turbidite flows in marine, deep-sea, or relatively deep-sea conditions. Sediments from Troynoy Island could have accumulated in shallow waters, as well as coastal marine settings.