2D and 3D fabric quantification of conduit textures to understand eruption dynamics and mechanisms: unique in situ example of Mt Unzen

文森山火山的文森科学钻探项目(USDP)穿透了火山系统的关键部分--岩浆管道；但这条管道很少被研究，因为它的样本很少。在这项研究中，我们可以获得这些独特的现场样本，这使我们能够调查被认为是上一次喷发(1991-1995年)的管道。众所周知，该系统是周期性的，记录在这些导管岩石中的结构信息包含有关岩浆运动、周期性和周期性岩脉侵位以及喷发动力学的关键信息，这对理解温岑山以及俯冲带上许多其他建造穹顶的火山非常重要。该项目专注于进行高分辨率的2D和3D观测，以量化纹理信息(孔隙度、矿物排列等)。保存在管道样品中；可用于揭示岩浆供应的不同阶段以及流速和/或变形(应变率)变化的结构。该项目从项目组的专业知识广度中受益匪浅，并已使用所有预定方法进行了全面的多学科可行性研究。这项工作的关键是非破坏性3D成像的能力，以准确地确定这些极其有限的样本体积中的结构，从而允许仔细放置和最小破坏性分析所需。我们的分析将使用最新的二维扫描电子显微镜和三维X射线层析成像方法来定义这些组构的性质，与管道形成、层流和/或湍流有关，以及从脆性变形到韧性变形的转变，所有这些都影响喷发机制。通过综合岩心结构信息，我们将从额外的磁性组构、岩石力学数据和有限的地球化学分析中获得这些信息，从而更好地了解从初始侵入到后期热液蚀变的所有输导过程。此外，通过将观测到的导管结构与在喷发表面样品中看到的结构联系起来，该项目还将能够更好地解释用于评估喷发机制和火山稳定性的现场和地球化学数据。预期的成果包括：更好地了解文森山系统，更好地解释保存在喷发物质中的结构信息(以限制深处的行为)，以及改进关于管道中岩浆行为的概念和力学-流变学模型。这项工作的重点是从温岑山管道获得的特殊和独特的样本，但结果将立即转移到俯冲区的其他穹顶火山。

The Unzen Scientific Drilling Project (USDP) at Mt Unzen volcano penetrated the magmatic conduit, a key part of the volcanic system; but one that is little studied as it is rarely sampled. In this study we have access to these unique in situ samples, which allows us to investigate what is thought to be the conduit of the last eruption (1991-1995). The system is known to be cyclic and the textural information recorded in these conduit rocks holds key information about magmatic movement, periodic and cyclic dike emplacement, and eruption dynamics that is important for understanding Mt Unzen; and many other dome-building volcanoes at subduction zones. The project focusses on making high resolution 2D and 3D observations in order to quantify the textural information (porosity, mineral alignments etc.) preserved in the conduit samples; textures that can be used to reveal the different stages of magma supply and changes in flow-rate and/or deformation (strain-rates). The project benefits significantly from the breadth of expertise in the project group, and a full multi-disciplinary feasibility study has been performed using all the intended methods. Key of the work is the ability for non-destructive 3D imaging to accurately define the structures in these extremely limited sample volumes, allowing careful placement and minimal destructive analysis to be required. Our analysis will use the latest 2D SEM and 3D X-ray tomographic methods to define the nature of these fabrics in relation to conduit formation, laminar and/or turbulent flow, and the transition from brittle to ductile deformation which all effect eruption mechanisms. By integrating the core textural information we will obtain that from additional magnetic fabric, rock mechanical data and limited geochemical analysis we will gain a better understanding of all conduit processes: from initial intrusion to the later stage hydrothermal alteration. Furthermore, by linking the observed conduit textures to those seen in erupted surface samples, the project will also enable better interpretation of field and geochemical data used to assess eruption mechanisms and volcano stability. The intended outcomes include: a better understanding of the Mt Unzen system, a better framework for interpreting textural information preserved in erupted material (to constrain behavior at depth), and improved conceptual and mechanical-rheological models of the behaviour of magma in conduits. This work focusses on the exceptional and unique samples available from conduit of Mt Unzen, but will have results that are immediately transferable to other dome-building volcanoes at subduction zones.