NSFGEO-NERC: Physical and Chemical Constraints on Large-volume Pyroclastic Blasts: The Campanian Ignimbrite Eruption, Italy

概述：Campanian火山灰岩是从一个稀释的火山碎屑密度流，伴随着Campi Flegrei的破火山口崩溃侵位。海流到达距离喷口80公里以上的地方，沉降物覆盖350万平方公里，距离喷口至少2 500公里。要产生一个明显超过一公里厚的电流，需要大量的气体，但是这些气体是从哪里来的呢？提议小组最近的工作发现，坎帕尼亚火山灰岩的侵位温度高于580摄氏度，表明电流在运输过程中并没有冷却得太多，这反过来又意味着大气气体的夹带量很小，喷发持续时间很短。岩浆气体可能是重要的，但如果这是唯一的来源，则需要在喷发前非常高水平的溶解气体。过热的热液水（估计在500 oC在5公里深的今天）可能是一个额外的气体来源。我们建议：1）详细的野外调查，以更好地描述坎帕尼亚火山灰岩地层，以连接远端和近端沉积，并确定火山事件的相对时间; 2）对坎帕尼亚期火山灰岩产物进行详细的岩石学研究，特别是通过进行完整的挥发分分析利用傅立叶变换红外光谱、离子探针和电子探针研究了熔融包裹体和磷灰石微斑晶中H2O、CO2、S、F和Cl的含量;和3）一个实验研究的冷却速率的Campanian火山灰岩喷发产物，使用的技术，研究玻璃化转变温度atvarying应变率和残余watercontents.Intellectual优点：我们建议测试的假设，即持续稀释PDCs可能是由气体驱动的岩浆和/或热液系统，而不是占主导地位的大气气体纳入柱和流。这将通过将实地观察和测量与内部岩浆过程联系起来，扩大我们预测火山灾害的能力。坎帕尼亚火山灰岩有近端和中间/远端沉积物，难以相互关联。最近的进展，地球化学和磁性技术用于相关的远沉降将适用于熔结凝灰岩和近沉积。碎屑的冷却历史将使用最近开发的方法来分析玻璃化转变温度和流变学的变化。反算开放体系脱气过程中的挥发分浓度是一项新技术，它将揭示坎帕尼亚期英云闪长岩岩浆历史的许多信息。了解热液流体的潜在作用？增压？更广泛的影响：那不勒斯地区是世界上火山风险最高的地区之一，约有400万人生活在受坎帕尼亚火山灰岩影响的地区（忽略生活在沉降区的人- > 1亿）。了解导致这种高流动性水流的岩浆/热液条件，将有助于更好地评估随着水流条件变化而产生的风险。我们将与Vesuviano观察站的工作人员合作，因此我们的结果将被纳入他们的风险评估。这个拟议的NSF/NERC项目将促进美国，英国和意大利之间的重大国际合作，并将纳入博士/硕士学生和博士后研究人员的形式代表性不足的群体的教育。

Overview:The Campanian Ignimbrite was emplaced from a dilute pyroclastic density current that accompanied caldera collapse of the Campi Flegrei. The currents reached over 80 km from the vent area and the fallout covers 3.5 million km2, reaching at least 2500 km from the vent. Abundant gas is needed to produce a current that was apparently more than a kilometer thick, but where did this gas come from? Recent work by the proposing team found that emplacement temperatures of the Campanian Ignimbrite were above 580oC, indicating that the current did not cool off very much during transport, which in turn implies minimal entrainment of atmospheric gases and a very short eruption duration. Magmatic gases are likely important, but very high levels of dissolved gas prior to eruption would be needed if that is the only source. Superheated hydrothermal water (estimated at 500oC at 5 km depth today) may be an additional gas source. We propose 1) detailed field investigations to better characterize the Campanian Ignimbrite stratigraphy, in order to link distal and proximal deposits and to define the relative timing of volcanic events; 2) a detailed petrologic study of Campanian Ignimbrite products, notably by performing complete volatile analysis (H2O, CO2, S, F and Cl) of melt inclusions and apatite microphenocrysts via Fourier Transform Infrared (FTIR) spectroscopy, ion probe, and electron microprobe; and 3) an experimental investigation of the cooling rates of Campanian Ignimbrite eruptive products, using a technique that studies the glass transition temperature atvarying strain rates and residual water contents.Intellectual Merit:We propose to test the hypothesis that sustained dilute PDCs may be driven by gas sourced from the magmatic and/or hydrothermal systems, rather than dominantly from atmospheric gases incorporated into the column and flow. This would extend our ability to forecast volcanic hazards by linking field observations and measurements to internal magmatic processes. The Campanian Ignimbrite has proximal and medial/distal deposits that are difficult to correlate. Recent advances in geochemical and magnetic techniques used to correlate the distal fallout will be applied to the ignimbrite and proximal deposits. Cooling histories of clasts will be traced using recently developed methods to analyze glass transition temperatures and rheological changes. Back-calculating volatile concentrations during open-system degassing is a new technique that should reveal much about the Campanian Ignimbrite magma history. Understanding the potential role of hydrothermal fluids in ?supercharging? an eruption would require some re-thinking of current models and interpretations of datasets, as hydrothermal water may not appear in many petrologic measurements of gases.Broader Impacts:The Naples area has one of the highest volcanic risks in the world, with about 4 million people living in the area that was affected by the Campanian Ignimbrite (ignoring the people living in the fallout zone - >100 million). Understanding the magmatic/hydrothermal conditions that led to such a high-mobility current would allow a better assessment of the risks as current conditions change. We will be working with personnel from the Osservatorio Vesuviano, so our results will be incorporated into their risk assessments. This proposed NSF/NERC project will foster a significant international collaboration between the US, UK, and Italy and will incorporate the education of underrepresented groups in the form of PhD/MS students and post-doctoral researchers.