Minerals with Mixed Anion Radicals in Fumarole-Transformed Crustal Micro Xenoliths as a New Phenomenon of Present-Day Volcanism

Abstract

This paper reports a study of xenoliths sampled in marine sedimentary carbonate rocks in fumaroles of the crater zone in the Second Cone of the GTFE (Great Tolbachik Fissure Eruption) North Vent. These rocks have been subjected to the action of the GTFE exhalative pneumatolytic fluids, resulting in carbonates giving rise to numerous compounds with mixed carbonate-sulfate-chloride anion radicals, which are treated as two interclass and nine intertype crystal-chemical hybrids. The patterns identified in the altered micro xenoliths, which consist in inhomogeneities of mineral paragenesis, are treated here as resulting from successive epigenetic transformation of the original carbonates to, at first, sulfate carbonates, then to carbonate sulfates, and subsequently to chloride-carbonate-sulfates and chlorides. Judging by an absence of signs of phase heterogeneity, the crystal-chemical hybrids studied here are homogeneous solid-phase mixtures of carbonates, sulfates, and chlorides in varying proportions. The carbonates in the micro xenoliths have isotopic compositions of carbon (δ¹³С_PDB = –5.34 ± 0.62‰) and oxygen (δ¹⁸O_SMOW = 24.09 ± 1.05‰) that are consistent with carbonates to be found in marine sedimentary limestones that were redeposited during volcanogenic transportation. The sulfate sulfur has the isotopic composition (δ³⁴S = 1.5–2‰) varying within the range of variation established for sulfates of volcanogenic origin. In the carbonaceous particles associated with micro xenoliths, the isotopic composition of carbon (δ¹³C_PDB = –27.37 ± 2.97‰) and of nitrogen (δ¹⁵N_Air = 6.74 ± 2.48‰) tend toward the mode in the distribution of these values in the ejecta of present-day continental volcanism. The crystal-chemical hybrids identified here furnish a typomorphic criterion for the exhalation fumarole facies and are treated as a previously unknown phenomenon of present-day volcanism.