To the problem of origin of the Bug series rocks

• Datum: 2019
• 1. Verfasser: Usenko, O. V.
• Format: Artikel
• Sprache: Russisch
• Veröffentlicht: S. Subbotin Institute of Geophysics of the NAS of Ukraine 2019
• Schlagworte: the Ukrainian shield; the Bug series; isotopic age; Proterozoic; carbonatites; graphite; ferruginous-silicon-carbonate formation
• Online Zugang: https://journals.uran.ua/geofizicheskiy/article/view/177365
• Назва журналу: Geofizicheskiy Zhurnal

The age of the Bug series rocks is an object for discussion. Isotopic methods do not give a distinct answer, because in the same outcrop, the same sample and even in the same crystal of zircon several dates of formation are to be found with evident significance. Involvement of additional criteria is required to determine the time of the Bug series formation. While examining the phase composition and the initial source of the material we need taking into account temperature and pressure distribution in the depth of formation of rocks, which are on the surface nowadays. Mineral and chemical composition of rocks and tectonic structure of including patterns have been considered. It has been shown that the composition of the Bug series is an indicator of time of formation. Carbonatites and calcyphyres, carbonate-magnetite rocks are not produced earlier than ~2.0 Ga ago. A considerable  part of the stratum is presented by high-clayish and graphite shale, quartzite, and ultrabasite that occur  jointly only in this period of time.  Arrangement of the structures is subdued to tectonic control by zones of deep faults. Smaller fault zones are determinative in the pattern of structures themselves and in manifestations of metasomatic processes. By the moment of their formation the level outcropped on the modern surface occurred at a depth more than 20 km that makes sedimentary nature of composing rocks doubtful. It has been shown that the most part of rocks attached to the Bug series are crystallization  products of magmatic melts as well as carbonate, silicate (water-silicate with chlorine), hydrocarbon fluids in faults (permeable zones) of crystalline basement in diapason of PT-conditions, corresponding to high amphibolites-granulites metamorphic facies. The pattern of these structures in projection is similar to the section of volcano-tectonic apparatuses at a depth not less than 20 km. In the structures small by their area, the rocks formed at different depths (from 300 to 200 km) from melts and fluids in different chemical media are presented. High temperature multiple metasomatism has been superposed. A conclusion has been made that the pattern of the structures of Khashchevato-Zavalye block and the Golovaniv suture zone does not reflect the succession of primary sedimentary rocks occurrence but a result of multiple crystallization and metasomatic re-crystallization  of melts and fluids.