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Evaluation of volcanic gas analyses from Kilauea volcano

1980; Elsevier BV; Volume: 7; Issue: 3-4 Linguagem: Inglês

10.1016/0377-0273(80)90034-7

1872-6097

T. M. Gerlach,

Geological and Geophysical Studies

Much of the chemical variation and disequilibrium in Kilauean volcanic gas analyses is the result of contamination by meteoric water and, to a lesser extent, organic matter. Contamination by meteoric water is extensive in some samples, causing variations of two to three orders of magnitude in atomic H/C. severely contaminated with meteoric water that did not equilibrate with the “Magmatic” gases and consequently gives the analyses a disequilibrium appearance. When the contaminating H2O is removed, the analyses converge to equilibrium mixtures in the temperature range 1085°C to 1185°C with O2 fugacities slightly above those for the quartz-magnetite-fayalite buffer. The restored analyses are richer in CO2 (18–50%) and SO2 (10–21%) and poorer in H2O (37–70%) than are the original analyses. There is no single gas phase composition for erupting Kilauea basalts. The restored J-series gases and the higher quality gases collected from Kilauea since 1920 form a spectrum of gas compositions related by CO2 content. A trend of decreasing CO2 with progressive outgassing is suggested. The extremes in the spectrum of compositions, based on presently available data, range from an “early” magmatic gas containing 50% CO2, 35% H2O, and 15% SO2 to a more evolved gas with 70% H2O, 10% CO2 and 20% SO2. The common presence of hydrocarbons and anomalously low atomic S/C in several Kilauea gas analyses is due to contamination of erupting lavas with organic materials. A similar origin also applies to above background levels of environmentally hazardous organohalogens in volcanic gases. Thermodynamic calculations indicate these compounds would be virtually absent in gases erupted from lavas at temperatures above 500–600°C.