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Silicate-sulfide liquid immiscibility in modern arc basalt (Tolbachik volcano, Kamchatka): Part II. Composition, liquidus assemblage and fractionation of the silicate melt

Citation

Kamenetsky, VS and Zelenski, M and Gurenko, A and Portnyagin, M and Ehrig, K and Kamenetsky, M and Churikova, T and Feig, S, Silicate-sulfide liquid immiscibility in modern arc basalt (Tolbachik volcano, Kamchatka): Part II. Composition, liquidus assemblage and fractionation of the silicate melt, Chemical Geology, 471 pp. 92-110. ISSN 0009-2541 (2017) [Refereed Article]

Copyright Statement

2017 Elsevier B.V. All rights reserved.

DOI: doi:10.1016/j.chemgeo.2017.09.019

Abstract

Olivine-hosted inclusions of silicate and sulfide melts, Cr-spinel and pyroxene were studied to estimate magma composition, temperature, pressure, and fO2 at the onset and during the silicate-sulfide immiscibility in modern arc basalt from Tolbachik volcano, Kamchatka arc. We demonstrate that the olivine phenocrysts hosting sulfide and silicate melt inclusions belong to the same population. The compositions of the silicate melt inclusions in most primitive olivine (8891mol% Fo) represent moderately oxidized (~QFM+1.1) high-MgO (up to 1212.6wt%) and high CaO/Al2O3 (0.81.2) melt that has abundances and ratios of the lithophile trace elements typical of island arc magmas. The initial volatile contents in parental Tolbachik magma are estimated from the melt inclusions and mass-balance considerations to be at least 4.9wt% H2O, 2600ppm S, 1100ppm Cl, 550ppm F, and 1200ppm CO2. These data are used to calculate the temperature (~1220C) and minimum pressure (3kbar) at which the beginning of crystallization and exsolution of sulfide melt took place. The presence of anhydrite, especially ubiquitous in the crystallized silicate melt associated with sulfide globules, suggest that much higher sulfur abundances prior to degassing and sulfate immiscibility and/or crystallization should be expected. We tentatively considered hydrothermal accumulations of sulfur (elemental, sulfate and sulfide) in the volcanic conduit responsible for local contamination and oversaturation of the Tolbachik magma in sulfur and related sulfide immiscibility. Coexisting sulfide and sulfate can be also interpreted in favor of the magmatic sulfide oxidation and related generation of S-rich fluids. Such fluids are expected to accumulate metals released from decomposed sulfide melts and supply significant epithermal mineralization, including native gold.

Item Details

Item Type:Refereed Article
Keywords:sulfide, immiscibility, olivine, magma, melt inclusions, volatiles, island-arc, Tolbachik volcano, geochemistry
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and Metamorphic Petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Kamenetsky, VS (Professor Vadim Kamenetsky)
Author:Kamenetsky, M (Dr Maya Kamenetsky)
Author:Feig, S (Dr Sandrin Feig)
ID Code:121876
Year Published:2017
Deposited By:CODES ARC
Deposited On:2017-10-18
Last Modified:2017-11-13
Downloads:0

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