Tephra from the Island Intra-Plate-Oceanic Volcano Cumbre-Vyaha (Eruption 2021)

Abstract

Comprehensive mineralogical and geochemical studies of a representative sample of tephra from the Cumbre-Vyaha volcano (2020–2021 eruption), which has a gravel-psammitic granulometric composition and is characterized by an anomalously high degree of particle vesicularity, have been carried out. In terms of bulk chemical composition, this tephra corresponds to the transition from alkaline picrobasalts to alkaline basalts, differing fundamentally from the tephra ashes of marginal continental volcanoes. The studied tephra contains 45 trace elements with a total content of up to 2333 ppm, which exceeds that in the tephra of island-arc volcanoes. According to the ratio of geochemical criteria, tephra from Cumbre-Vyaha correspond to the average values for within-plate volcanoes in the oceans. The geochemical feature of the studied tephra is a strong enrichment in lanthanides, noble and platinoid metals. H2, CO, CO2, H2O, CH4, C2H4, C2H6, C3H6, C3H8 were found in the composition of the lithogenic gas phase separated by heating from the studied tephra. The proportions between inorganic components in the gas phase generally correspond to the boundary region between crustal and mantle-crustal derivatives, but a relatively low water content is found. Olivine of composition Fo73–84, essentially diopside clinopyroxene, andesine-bytovnite plagioclases, chrome spinels, phase-homogeneous solid solutions of ilmenite in magnetite, phases of Ni-Cu-bearing native iron, quartz, and sodium hydroxyl chlorides were identified and studied in microlites. In addition, dispersed carbon matter with carbon isotopic composition δ13СPDB = –30…–24‰ was found in the Cumbre-Vyaha tephra, which corresponds to the carbon isotope composition in abiogenic carbonaceous substances of volcanic origin. The totality of the results of mineralogical and geochemical studies characterizes the Cumbre-Vyaha volcano as a typical representative of within-plate oceanic plume volcanoes.