Eruption mechanisms and crystal textures

1.亚液态岩浆的粘度测量：亚液态岩浆中含有各种形状和大小的晶体，它们对体粘度的影响以前没有研究过。我们安装了一个带粘度计的气氛控制炉，用伴随取样法测量了体粘度，并从玻璃分析中评估了熔体粘度，分析了晶体结构。1707年富士火山高铝玄武岩的液相相为斜长石，斜长石板条极薄，与常用的爱因斯坦-罗斯科-马什方程偏差达4倍。另一方面，九州北部的碱性橄榄石玄武岩以橄榄石为液相相，且有20 vol%的轻度薄斜长石存在，但没有引起ERM方程的偏差，这可以通过评价Krieger-Dougherty方程中的参数来解释。通过高压实验评价了云仙火山1991 ~ 1995年英安岩岩浆混合的末段岩浆条件，并对云仙英安岩中角闪石与熔体的Cl/OH分割系数进行了实验测定，结果表明角闪石的Cl/OH分割系数与Mg/(Mg+Fe)比值密切相关。结果表明，云仙英安岩中振荡分带角闪石斑晶中Cl含量的显著变化是由于低温岩浆的反复脱气和流体相的输入所致。另一项对云仙英安岩的实验表明，Cl.3的存在增加了硫的溶解度。实验评价了压力和含水量对斜长石与玄武岩熔体Ca-Na分配系数的影响，结果表明，高安斜长石结晶的最佳条件是弧拉斑岩中2-3kb水饱和条件。探讨了高镁质火山岩的地球化学和岩石学成因条件。

1.Viscosity measurement of subliquidus magmas : Subliquidus magmas contain crystals of various shapes and size, and their effect on bulk viscosity has not been studied previously We installed an atmosphere-controlled furnace with viscometer, and measured bulk viscosity with concominant sampling, and evaluated the melt viscosity from the glass analyses, and analyzed the crystal textures. The 1707 high-alumina basalt of Fuji volcano has plagioclase as liquidus phase, and very thin plagioclase laths caused deviation from the commonly-used Einstein-Roscoe-Marsh equation by a factor of 4. On the other hand, an alkali olivine basalt of NW Kyushu has olivine as liquidus phase and presence of 20 vol% of mildly thin plagioclase did not cause deviation from the ERM equation, which can be explained by evaluating the parameters in the Krieger-Dougherty equation.2.We evaluated the conditions of the end member magmas of magma mixing for the 1991-1995 dacite of Unzen volcano by high-pressure experiments, and also conducted experiments to determine the Cl/OH partition coefficient between hornblende and melt in the Unzen dacite, showing the strong dependence of the partition coefficient on the Mg/(Mg+Fe) ratio of hornblende. This result suggest that marked variation of Cl content of oscillatory zoned hornblende phenocryst in the Unzen dacite was caused by repeated degassing and input of fluid phase in the low-temperature magmas. Another experiments on the Unzen dacite showed solubility of sulfur is increased by the presence of Cl.3.Effect of pressure and water content on the Ca-Na partition coefficient between plagioclase and basaltic melt was evaluated experimentally, and it was shown that optimal condition for crystallization of high-An plagioclase is 2-3kb water saturated condition in arc tholeiite.4.Genetic conditions of high-magnesian volcanic rocks are examined geochemically and petrologically.