HR: 0800h
AN: V31D-0660    [Abstracts]
TI: Experimental Reproduction on the Hydrous Alteration with Super-Critical Fluid Flow
AU: * Isobe, H
EM: isobe@sci.kumamoto-u.ac.jp
AF: Faculty of Science, Kumamoto Univ., Kurokami, Kumamoto, 860-8555 Japan
AB: Behavior of high-pressure fluid flow and permeability of rocks have close relation to volcanic eruptions. Especially, phreatomagmatic eruptions caused by excess pressures of the fluid degassed from magma body or heated water contacted with magma or high temperature rocks in volcanoes. Alteration, dissolution and / or precipitation processes of rocks and minerals coexisting with high temperature fluid can change permeability of rocks by spreading of the fluid path or obstruction with precipitated minerals. Kinetics of flowing super-critical fluid - rock interaction is essential to understand accumulation or release of excess pressure of the fluid. In this study, experimental reproduction on the hydration and alteration processes of rocks and minerals with super-critical fluid were carried out with a fluid flow apparatus. Starting materials of the experiments is powdered rhyolitic obsidian. Approximately 55g of the starting material are placed in a SUS316 sample tube sealed to an outlet of the pressure vessel with pure Ti gaskets. Inner diameter and length of the sample tube are 9.4mm and 572mm, respectively. Temperature gradient of the pressure vessel is controlled by triple electric furnaces. Run products of the powdered samples are retrieved by cutting off the sample tube. Experimental pressure is 50MPa. Flow rate of distilled water is 0.1ml / minute pumped by a low speed high-pressure pump at room temperature. Temperature of the sample is approximately 450°C at the first half of the sample tube, then decreased to approximately 310°C at the outlet of the sample tube. Run duration is 8 days or 3 days. Obsidian grains partially dissolved and changed to porous at most of the sample tube. Alteration products of the volcanic glass including clay minerals, cristobalite and plagioclase occur in grain boundaries and cemented grains within a few centimeters from the outlet of the sample tube. Effective sealing for fluid flow by the alteration products can be only found at approximately 330°C or lower temperature. Accumulation of the high-pressure super-critical fluid body may only appear when the fluid body is surrounded by the low temperature alteration products.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
DE: 8430 Volcanic gases
DE: 8445 Experimental volcanism
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005