Underwater-marine volcanic rocks in the upper riphean deposits of Pay-Khoy

The association of volcanic-sedimentary and volcanogenic rocks (travertine-gyaloclastite-lawaclastite) was studied in Upper Riphean section of Pay-Khoy. Its presence is on indicator of the early stage of underwater volcanism. Travertine was found on the contact of lenticular bodies of secondary microbial dolomite and submarine volcanic formations. Travertine contains fragments of basic volcanic buried in a heterogeneous carbonate matrix. It has a complex structure and consists mainly of dolomite with a small admixture of ferruginous chlorite, biotite, muscovite, sulfide and iron hydroxide. Four carbonate generations, different by their morphology and genesis, were determined. These generations reflect stages of epigenetic change and processes of mineral formation. The isotopic composition of carbon and oxygen shows that these rocks were formed in shallow water conditions of the epicontinental warm-water basin. The gialoclastites are composed by rounded fragments of basic volcanic rocks and clay-mica filler. Their chemical composition corresponds to subalkaline basalt of the island-arc stage. Ferruginous chlorite and illite dominate in the clay fraction of the filler. In alkaline environment sedimental and diagenetal changes led to the illites formation. The composition of lithoclast in the lavaclastes repeats the composition of gyaloclastic. It is petrochemically similar to low-Ti magnesia alkaline basaltic of the Middle Morozov subformation The formation of the association under study occurred in the area of a microbial buildup located near the magma chamber. The travertines formation resulted from the interaction of the Ca, Mg, Fe cations with carbon dioxide from hydrothermal solution or released during the decomposition of buried biogenic mass. The appearance of gialoklastite indicates a single ash-lava ejection that preceded the accumulation of layered volcanics and volcanomictic-terrigenous rocks of the Morozov formation.