Halogen-dominant mineralization at Mt. Calvario dome (Mt. Etna) as a response of volatile flushing into the magma plumbing system

Abstract

The exceptional occurrence of fluorine-rich mineral phases in the benmoreitic lava dome of Mt. Calvario (south-western flank of Mt. Etna) has given the opportunity to understand the genetic process allowing their crystallization. Both primary and secondary mineral associations were found, namely: plagioclase, clinopyroxene, olivine, fluorapatite and iron oxides as primary assemblage, whereas fluoro-edenite and fluorophlogopite, ferroan-enstatite, hematite, pseudobrookite and tridymite as secondary mineralization. In addition to some major and trace elements (e.g., Fe, Ti, Na, K, P, Ba, Rb, Sm, Zr), particularly fluorine and chlorine concentrations of the whole rock are significantly higher than other Etnean prehistoric benmoreites, and cannot be accounted for common differentiation processes in the feeding system. The selective enrichment in some elements has been here attributed to volatile flushing occurring in the plumbing system, with fluid/melt ratio of 0.65:1. The resulting high amount of fluorine, coupled with its high solubility even at low pressure for benmoreitic melts, finally led to nucleation and growth of F-rich mineral phases during syn- and post-eruptive conditions

Fluorophlogopite from Piano delle Concazze (Mt. Etna, Italy): Crystal chemistry and implications for the crystallization conditions

“…These compositional differences should reflect distinct physical-chemical conditions at the time of crystallization, in relation primarily to the amount of available volatiles into the feeding system. As noted by some authors Mazziotti-Tagliani et al 2012a, 2012b, the occurrence of the F-rich mineralogical phases (particularly fluorophlogopite) is attributed to volatile flushing of a resident magma reservoir. This mechanism can produce selective transfer of some elements that are carried by a gas phase, finally leading to anomalous concentrations of elements with great affinity with fluids or that can be complexed (Rittmann 1962;Caroff et al1997;Greenough et al 1999;de Hoog and van Bergen 2000;Ferlito et al 2008;Nicotra et al 2010).…”

A New Porphyry Mo Mineralization at Aisymi-Leptokarya, South-Eastern Rhodope, North-East Greece: Geological and Mineralogical Constraints

“…Further field and laboratory work aims to establish the mechanism for elemental enrichment in the studied mineralization, by testing the hypothesis of vapor versus fluid transportation as has been observed in both active volcanoes (e.g., Etna, Italy, Lewotolo and Merapi, Indonesia, Kudryavy, Russia) and magmatic-hydrothermal systems (porphyry and epithermal systems) [46][47][48][49][50][51][52].…”

Insights Into the Eruptive Dynamics of Small Caldera-Forming Eruptions: The Case Study of the Welded Scoriae of Vulcano (Aeolian Islands, Italy)

“…This process, usually called "volatileinduced differentiation" and also observed in some basaltic s.l. volcanic systems (Rittmann, 1962;Burnham, 1979;Caroff et al, 1997;Greenough et al, 1999;de Hoog and van Bergen, 2000;Ferlito et al, 2008;Nicotra et al, 2010;Mazziotti Tagliani et al, 2012;Nicotra and Viccaro, 2012a), is able to produce visible modification in the whole rock composition of magmas, which is also reflected in the crystallizing mineralogical phase. In the plagioclase case, volatile-induced differentiation would have significantly modified the FeO (for effect of the increased f O 2 ) content in correspondence of the MI alignments, a feature which is never observed in the SL samples.…”