Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes

A case study from Ciomadul volcano (SE Carpathians)

Balázs Kiss, S. Harangi, Theodoros Ntaflos, Paul R D Mason, Elemér Pál-Molnár

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

Ciomadul is the youngest volcano in the Carpathian-Pannonian region produced crystal-rich high-K dacites that contain abundant amphibole phenocrysts. The amphiboles in the studied dacites are characterized by large variety of zoning patterns, textures, and a wide range of compositions (e.g., 6.4-15 wt% Al2O3, 79-821 ppm Sr) often in thin-section scale and even in single crystals. Two amphibole populations were observed in the dacite: low-Al hornblendes represent a cold (900 °C) mafic magma. Amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage (~8-12 km). This was also the place where the erupted dacitic magma was formed during the remobilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple-zoned and composite amphiboles. This includes reheating (by ~200 °C) and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population (including pargasites). Breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes, suggesting that pre-eruptive heating and mixing could take place within days or weeks before the eruption. The decompression rim of pargasites suggests around 12 days of magma ascent in the conduit. Several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the Ciomadul, but in our dacite the two amphibole population can be found even in a single crystal (composite amphiboles). Our study indicates that high-Al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone; thus, they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes. The simple-zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the Al-tschermak substitution can be recognized, suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation.

Original languageEnglish
Pages (from-to)1-27
Number of pages27
JournalContributions to Mineralogy and Petrology
Volume167
Issue number3
DOIs
Publication statusPublished - 2014

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Amphibole Asbestos
Plumbing
Volcanoes
amphiboles
volcanoes
amphibole
volcanology
volcano
arcs
dacite
crystal
pargasite
magma
Crystals
Crystallization
hornblende
heating
crystals
composite materials
Composite materials

Keywords

  • Amphibole perspective
  • Amphibole texture and zoning patterns
  • Intermediate magmas
  • Magma mixing
  • Thermobarometry
  • Volcano plumbing system

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes : A case study from Ciomadul volcano (SE Carpathians). / Kiss, Balázs; Harangi, S.; Ntaflos, Theodoros; Mason, Paul R D; Pál-Molnár, Elemér.

In: Contributions to Mineralogy and Petrology, Vol. 167, No. 3, 2014, p. 1-27.

Research output: Contribution to journalArticle

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