Determination of volatiles in volcanic rocks and minerals with a Directly Coupled Evolved Gas Analyzing System (DEGAS) -Part I: Interpretation of degassing profiles (DEGAS-profiles) of minerals and rocks on the basis of melting experiments

K. Heide, C. M. Schmidt

Abstract


Volatile components in magma strongly influence many physical properties of melts and minerals. The temperature
resolved degassing analysis of volcanic crystalline and vitreous rocks gives detailed information about volatile compounds
in the melt. Aspecial high-temperature mass-spectrometry device in combination with a thermo-balance allows
a quantitative determination of different volatile species. It enables a differentiation between the primary gas
content in the magma and the gas released from decomposition of secondary alteration products. The gas release
profiles give the following indications: i) during the littoral explosions of Pahoehoe lava the content of volatiles is
not changed by interaction with air or sea water; ii) the degassing profiles of vitreous black sand verify the primary
content of volatiles in the erupted melt, only CO2 was detected; iii) the oxygen release profile gives significant indications
for oxygen undersaturation of the erupted magma; iv) remelting of black sand in air at 1450°C for 0.45 h
causes an oxygen saturation of the basaltic melt; v) remelting of black sand in argon atmosphere confirms the oxygen
undersaturation of the melt; vi) remelting of black sand-black shale mixtures affects a significant change in the
degassing profiles, especially in CO2-release. With the first investigations we can demonstrate that gas release
curves of volcanic rocks are qualified for a) detection of the primary gas content of erupted magma; b) detection of
alteration processes of the igneous glass; c) detection of contamination of the magma with adjacent rocks.

Keywords


volatiles;magmatic rocks;basaltic glass;degassing;Hawaiian lava;remelting;blacksand

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References


DOI: https://doi.org/10.4401/ag-3228
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X