A microstructural analyses of groundmass of dacite lavas, and their flowage and solidification processes.

英安岩熔岩基质及其流动和凝固过程的微观结构分析。

• 批准号: 11640447
• 负责人: MIYAKE Yasuyuki
• 金额: $ 2.24万
• 依托单位: Shinshu University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640447/
• 关键词: Dasite; lava; flowage; groundmass; cavitation; Unzen; Daisen; Yakedake; Hyaloclastite; キャビテイション

Such dacite lava domes as, Unzen-Fugendake, Daisen-Misen, Yakedake, and Miocene subaqueous dome at Katsurajima, Shimane Peninsula were investigated. Especially their microstructures and occurrences of cavities are studied. Following four results are obtained.1. Lavas that emplaced on steep slopes contain voids formed by mechanical processes. The voids vary from having ragged margins to sharp margins, and ragged margin voids are interpreted as failures in the ductile crystal mush magma. Voids with sharp margins are interpreted as brittle cracks formed when the rock had attained homogenous strength. These dilatant structures have been observed in upper, lower, proximal and distal parts of the lava flows. The dilatantancy and brittle flow structures observed are characteristic of dacite emplaced on the steep slopes.2. Pores in dacite lavas of three volcanoes in Japan (Unzen, Yakedake and Daisen) have characteristics unlike vesicles. Most of the pores have ragged walls marked by the protru … More sion of groundmass crystals and phenocrysts. The shapes of these pores range from irregular to planar. Many pores occur in 'pressure shadows' adjacent to plenocrysts. Some pores are crack-like and pass around phenocrysts and have blunt terminations. Most of the pores are interpreted as the result of failure of the magma by flow during ductile-brittle transition. This phenomenon, known as cavitation, is well established in hydraulics and the material sciences. Cavitation of the lavas in this study was promoted by steep slope of emplacement, subtle mechanical contrasts between bands, and strain intensification around rigid crystals and lithic fragments. Cavitation in lava can extract volatiles from magma causing premature embrittlement and weakening. Cavitation is inferred to be critical to the initiation of lava-front pyroclastic flows.3. Dacite magma emplaced subaqueously show band structures caused by rapid cooling by water. In the case of Katurajima lava dome in Shimane Peninsula, Miocene in age, the bands consists of mafic recessive zone and felsic prominent zones, SiO2 variation being58-74wt.%. Such a wide range variation, along with the groundmass structures are interpreted by combination of rapid cooling by magma and magma differentiation at the vent.4. Subaqueous dacite lavas provide an example of hyaloclastite that were formed by invasion of water into the hot rock body. Such an invasive hyaloclastites can be distinguished from the formerly well described subaqueous autobrecciated lavas. In the shallow water, hyaloclastite can be formed not only by quench-contraction of hot rock but also by small explosion induced by magma-water interaction. Less

研究了在Katsurajima，Shimane Peninsula的Dacite熔岩域，例如Unzen-Fugendake，Daisen-Misen，Yakedake和中新世下浅的圆顶。尤其是它们的微观结构和腔体发生。以下四个结果获得了1。在钢槽上放置的熔岩包含由机械过程形成的空隙。这些空隙从边缘的边缘到尖锐的边缘不等，而毛边缘的空隙被解释为延性晶体肌岩浆中的故障。岩石附着均匀强度时，具有尖锐边缘的空隙被解释为形成的脆性裂缝。这些膨胀结构已在熔岩流的上，下，近端和不同部分中观察到。观察到的扩张物实验室是钢斜坡上放置的dacite的特征。2。日本三个火山（未祖，Yakedake和Daisen）的毛孔中的孔具有与蔬菜不同的特征。大多数毛孔的墙壁上都以凹凸的标记……地面晶体和表晶的更多含量。这些毛孔的形状范围从不规则到平面。许多孔出现在与全体晶体相邻的“压力阴影”中。有些毛孔是裂缝状的，并在全体晶体周围传递，并具有钝性的终止。大多数孔被解释为在延性脆性过渡过程中流量失败的结果。这种现象被称为空化，在液压和材料科学中已经很好地确定。这项研究中熔岩的空化是通过蒸汽斜率，带之间的微妙的机械对比度以及刚性晶体和岩性碎片周围的应变强度来促进的。熔岩中的空化可以从岩浆中提取挥发物，从而导致过早的互惠和减弱。假定对熔岩前火山碎屑流的启动至关重要。3。 dacite岩浆脱落的是由水快速冷却引起的带状结构。在Shimane半岛的Katurajima熔岩圆顶的情况下，年龄为年代，乐队由镁铁质隐性区和长英质区的突出区域组成，SIO2变化为58-74wt。％。如此宽的范围变化以及地面质量结构通过岩浆和岩浆分化在通风口的快速冷却来解释。4。水下岩石熔岩提供了一个透明岩的例子，这些熔岩是通过将水入侵到热岩体而形成的。这种侵入性的透明质层可以与以前描述的亚湿自动型熔岩区分开。在浅水中，透视质不仅可以通过热岩的淬灭来形成，而且还可以通过岩浆 - 水相互作用引起的小爆炸形成。较少的

项目成果

Smith, J.V.: "Textural evidence for dilatant (shear thickening) rheology of magma at high crystal concentrations."Jour.Volcanol.Geothermal Res.. 99. 1-7 (2000)

Smith, J.V.：“高晶体浓度下岩浆膨胀（剪切增稠）流变学的结构证据。”Jour.Volcanol.Geo Thermal Res.. 99. 1-7 (2000)

Smith,J.V.,Miyake,Y.and Oikawa,T.: "Interpretation of porosity in dacite domes as ductile brittle failure textures"Journal of Volcanology and Geothermal Research. (in print).

Smith, J.V.、Miyake, Y. 和 Oikawa, T.：“将英安岩圆顶中的孔隙度解释为延性脆性破坏纹理”火山学与地热研究杂志。

Smith J. V.: "Textural evidence for dilatant (shear thickening) rheology of magma at high crystal concentrations."Jour. of Volcanology and Geothermal Res.. in press.

Smith J. V.：“高晶体浓度下岩浆膨胀（剪切增稠）流变学的结构证据。”

Smith,J.V.: "Textural evidence for dilatant (Shear thickening) rheology of magma at high crystal concentrations."Jour nal of Volcanology and Geothermal Research. 99. 1-7 (2000)

Smith, J.V.：“高晶体浓度下岩浆膨胀（剪切增稠）流变学的结构证据。”火山学和地热研究杂志。

Smith, J.V.: "Dilatancy and brittle flow structures in dacite lavas emplaced on steep slopes in Japan."EOS. 80. F1090 (1999)

Smith, J.V.：“日本陡坡上英安岩熔岩的剪胀性和脆性流动结构。”EOS。