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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Viscosity measurements of subliquidus magmas: Alkali olivine basalt from the Higashi-Matsuura district, Southwest Japan
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Viscosity measurements of subliquidus magmas: Alkali olivine basalt from the Higashi-Matsuura district, Southwest Japan

机译：亚液相线岩浆的粘度测量：来自日本西南部东松浦地区的碱性橄榄石玄武岩

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We carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the Matsuura district, SW Japan, at subliquidus temperatures from 1230℃ to 1140℃ under 1 atm with NNO oxygen buffered conditions. Viscosity increased from 31 to 1235 Pa s with a decrease in temperature from 1230 to 1140℃. On cooling, olivine first appeared at 1210℃, followed by plagioclase at 1170℃. The crystal content of the sample attained 31 vol.% at 1140℃ (plagioclase 22%, olivine 9%). Non-Newtonian behaviors, including thixotropy and shear thinning, were pronounced in the presence of tabular plagioclase crystals. The cause of such behavior is discussed in relation to shear-induced changes in melt-crystal textures. Relative viscosities, η_r (=η_s/η_m, where η_s and η_m are the viscosities of the suspension and the melt, respectively), were obtained by calculating melt viscosities from the melt composition and temperature at 1 atm using the equation proposed by Giordano and Dingwell [Giordano, D., Dingwell, D.B., 2003. Non-Arrhenian multicomponent melt viscosity: a model. Earth and Planetary Science Letters, 208, 337-349.]. The obtained relative viscosities are generally consistent with the Einstein-Roscoe relation, which represents η_r for suspensions that contain equant and equigranular crystals, even though the crystal suspension analyzed in the present experiments contained tabular plagioclase and granular olivine of various grain sizes. This consistency is attributed to the fact that the effect of crystal shape was counterbalanced by the effect of the dispersion of crystal size. The applicability of the Einstein-Roscoe equation with respect to crystal shape is discussed on the basis of the present experimental results. Our experiments and those of Sato [Sato, H., 2005. Viscosity measurement of subliquidus magmas: 1707 basalt of Fuji volcano. Journal of Mineralogical and Petrological Sciences, 100, 133-142.] show that the relationship between relative viscosity and crystal fraction is consistent with the Einstein-Roscoe relationship for axial ratios that are smaller than the critical value of 4-6.5, but discrepancies occur for higher ratios.
机译：我们在NNO氧气缓冲条件下，在1atm的亚液相线温度从1230℃到1140℃的亚液相线温度下，对日本西南部松浦地区的碱橄榄石玄武岩晶体悬浮液进行了粘度测量和采样。粘度从31 Pa s增加到1235 Pa s，温度从1230 Pa降低到1140℃。冷却后，橄榄石首先出现在1210℃，然后斜长石出现在1170℃。样品的晶体含量在1140℃下达到31 vol。％（斜长石22％，橄榄石9％）。在板状斜长石晶体的存在下，非牛顿的行为，包括触变性和剪切稀化表现得很明显。讨论了这种行为的原因，涉及剪切诱导的熔体晶体织构变化。相对粘度η_r（=η_s/η_m，其中η_s和η_m分别是悬浮液和熔体的粘度），是通过使用佐丹奴和Dingwell提出的方程从熔体组成和1 atm的温度计算出熔体粘度而获得的[Giordano，D.，Dingwell，DB，2003。非阿伦多组分熔融粘度：模型。地球与行星科学快报，208，337-349。]。所获得的相对粘度通常与爱因斯坦-罗斯科关系（Einstein-Roscoe关系）一致，该关系表示包含等晶粒和等晶粒晶体的悬浮液的η_r，即使在本实验中分析的晶体悬浮液包含板状斜长石和各种粒径的粒状橄榄石。这种一致性归因于以下事实：晶体形状的影响被晶体尺寸分散的影响所抵消。在目前的实验结果的基础上，讨论了爱因斯坦-罗斯科方程对于晶体形状的适用性。我们的实验和Sato的实验[Sato，H.，2005。亚液相线岩浆的粘度测量：富士火山的1707玄武岩。矿物与岩石科学学报，100，133-142。]表明，当轴向比小于4-6.5的临界值时，相对粘度和晶体分数之间的关系与Einstein-Roscoe关系一致，但是会出现差异对于更高的比率。

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