高温顕微赤外分光法によるマグマの構造と水および脱水速度

概要

論文の詳細を見る
High temperature infrared (1R) microspectroscopy has been developed for the in-situ characterization of structure, water and dehydration behaviors of magmas. Natural rhyolitic glasses were measured for their change in structures and water up to 1500℃. Based on recent in-situ data of water in alkali-aluminosilicate glasses suggesting the presence of more OH than H_2O, in-situ dehydration kinetics of hydroxyl(-OH) species from rhyolitic glasses were studied in detail by the above method. First order reaction rates and activation energies were determined for a natural rhyolitic glass from Kozushima and Wada-Toge (Obsidian), Japan at temperature ranges of 500-600℃ and 800-950℃ respectively. Activation energy values for the dehydration of these glasses varies from 70 to 130 kJ/mol. By comparing these with our data on dehydration kinetics of hydrous polycrystalline quartz aggregates (agate; 34, 70 and 190 kJ/mol) and muscovite (440 kJ/mol). together with literature data on water diffusion in melts/glasses (50-120kJ/mol), the main rate-determining step of dehydration of rhyolitic glasses is considered to be the diffusion of water. The diffusion profiles of water in obsidian were detected by micro-IR line analysis and gave reasonable diffusion coefficients. These data were used to evaluate a typical time scale of volcanic degassing at around 550℃ in the order of several hours.
特定非営利活動法人日本火山学会の論文
1997-04-25