Collaborative Research: Structure, Conditions and Magmatic Processes Within an Active Volcano: Analysis of Samples from Boreholes Drilled into the Conduit of Unzen Volcano, Interna

该项目将使私人投资机构能够参与对正在由日本温泉科学钻探项目(USDP)钻探的钻孔和样品进行的国际合作调查。USDP是国际大陆钻探计划(ICDP)的一部分，该计划寻求将钻探作为一种工具来促进对地壳基本过程的了解。USDP的目标是了解作为一类重要的安山岩弧火山代表的温岑火山的喷发行为。在现已完成的一期钻探工程中，在火山大厦底部分别钻了750米和1500米的侧孔，以获得火山活动的完整物理化学记录。这一提议旨在继续一项为期一年的试点项目，该项目表明，目前的温泉岩浆系统已经持续了50万年，其特点是经常将分离的镁铁质岩浆注入成分非常恒定的地壳驻留的泥浆中。钻井项目下一阶段的智力目标将是：1)了解粘性岩浆在接近地球表面时的力学、化学和热学行为；以确定为什么Unzen是最初湿岩浆非爆炸性喷发的典范案例，以及3)。通过提供直接的地下观测，为前兆地震活动、形变和脱气提供解释，改进预测喷发的技术。研究人员建议使用光学、扫描电子显微镜、电子探针、XRF和LA-ICPMS技术来检查样品。特别是，近端单元将与侧翼钻井中遇到的单元相关联，将绘制热液蚀变带的地图，并识别侵入特征。最重要的是，将描绘出1991-1994年火山喷发的管道。为了限制脱气行为，将特别注意管道边缘是否存在侵入玻璃以及中心部分是否存在残余熔体。玻璃状穹顶熔岩与部分结晶管道材料(如果残留熔体)和结晶管道材料的比较将有助于确定未成岩浆的完整结晶路径。将确定管道宽度、管道内与脱气和冷却有关的结构变化、岩浆和围岩的合理流变性，以及管道流动和脱气对围岩的影响。就更广泛的影响而言，这项工作应提高对这种危险类型火山活动的认识和可预测性，这种火山活动近年来不仅影响到日本岛原，而且还影响到菲律宾皮纳图博火山和蒙特塞拉特苏弗里尔山火山附近的城镇。该项目在日本引起了公众的极大兴趣，一旦管道钻探开始，可能会在全球范围内做到这一点。因此，USDP团队计划在万维网上以英语、日语和德语近乎实时地向公众提供结果。作为团队中美国科学界的代表，调查人员将适当利用这一机会，在出现研究机会时向他们的美国同事介绍情况。这将有助于增加文森项目的专业知识广度，同时让美国人了解日本火山界非常丰富的资源、经验和想法。

This project will allow the PIs to participate in internationally collaborative investigations of boreholes and samples now being drilled by the Unzen Scientific Drilling Project (USDP), Japan. The USDP is part of the International Continental Drilling Program (ICDP), which seeks to use drilling as a tool to advance understanding of fundamental processes of Earth's crust. The goal of the USDP is to understand the eruptive behavior of Unzen as representative of an important class of andesitic arc volcanoes. In the now-completed first phase of the drilling project, flank holes of 750 m and 1500 m were drilled to the base of the volcanic edifice in order to obtain a complete physical and chemical record of the volcano's activity. This proposal aims to continue a one-year pilot project that has shown that the present Unzen magma system, which is characterized by frequent injection of fractionated mafic magma into a crust-resident slush of remarkably constant composition, has persisted for 500,000 years. The intellectual targets for the next phase of the drilling project will be: 1.) to understand how viscous magma behaves mechanically, chemically, and thermally as it approaches Earth.s surface; 2.) to determine why Unzen is such an exemplary case of non-explosive eruption of initially wet magma, and 3.) to improve techniques to forecast eruptions by providing direct subsurface observations that inform interpretation of precursory seismicity, deformation, and degassing. The investigators propose to use optical, SEM, electron microprobe, XRF, and LA-ICPMS techniques to examine the samples. In particular, proximal units will be correlated to units encountered in flank drilling, zones of hydrothermal alteration will be mapped, and intrusive features identified. Most importantly, the conduit that fed the 1991-1994 eruption will be delineated. In order to constrain degassing behavior, special attention will be paid to occurrence of intrusive glass on the margin of the conduit and residual melt in the central portion. Comparison of glassy dome lava with partially crystalline conduit material (if residual melt remains) and with crystalline conduit material will serve to define the complete crystallization path of Unzen magma. Conduit width, textural variations within the conduit related to degassing and cooling, plausible rheologies of the magma and wallrock, and effects of conduit flow and degassing on the wallrock will be determined. In terms of broader impacts, the work should improve the understanding and predictability of this dangerous type of volcanic activity, which has afflicted not only Shimabara, Japan but also towns near Pinatubo Volcano in the Philippines and Soufriere Hills Volcano in Montserrat in recent years. The project has attracted much public interest in Japan, and will likely do so worldwide once drilling to the conduit has begun. Accordingly, the USDP team plans to make results available to the public in near-real time in English, Japanese, and German over the Worldwide Web. As representatives of the US scientific community on the team, the investigators will make appropriate use of this opportunity to acquaint their American colleagues with research opportunities as they arise. This will serve to increase the breadth of expertise engaged in the Unzen enterprise, while at the same time acquainting Americans with the very substantial resources, experience, and ideas of the volcanological community of Japan.