Chemical and Isotopic Gradients around Bubbles in Volcanic Feeder Systems

火山馈线系统中气泡周围的化学和同位素梯度

• 批准号: 1249404
• 负责人: James Watkins
• 金额: $ 18.87万
• 依托单位: University of Oregon Eugene
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-02-01 至 2017-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1249404&HistoricalAwards=false
• 关键词: Chemical; Isotopic; Gradients; around; Bubbles

Volcanic eruptions are among the most spectacular, and potentially devastating, geological events on Earth?s surface. The explosivity of volcanic eruptions, and the hazards they pose, depend on how volcanoes outgas, or specifically, the amount and rate of gas bubble formation and efficiency of gas removal from rising magma. Although methods exist to estimate the total gas budget of parental and erupted lava, it is more difficult to get information about the timing and rates of bubble growth and gas loss as magma moves towards the Earth?s surface. This study offers a new perspective by focusing on small-scale textures and chemical gradients preserved around bubbles in volcanic glass. The research is based on the realistic assumption that slow diffusion may inhibit bubble-magma equilibrium, leading to H2O and CO2 gradients in the melt. The sign, magnitude, and length scale of these gradients can be measured using modern analytical techniques and they provide new clues for understanding the processes responsible for separating volatile species and their isotopes during bubble growth, resorption and removal from magma. Samples that will be investigated include bubbles in low- to high-silica volcanic glass and bubbles grown within experimental capsules. The study will focus largely on the behavior of H2O and CO2, two important components of volcanic gas that differ in their chemical diffusivities. Since H2O has a high diffusivity, its concentration profiles are likely to record changes in equilibrium solubility due to pressure, temperature, and chemical changes in volcanic feeder systems. Since CO2 has a low diffusivity, its concentration profiles are likely to contain information about rates of bubble growth or resorption and fracture healing. The study also includes a novel approach for investigating the relationship between chemical speciation and diffusion in the melt phase. Different dissolved species (e.g., OH and H2Om) have different masses and should therefore exhibit different degrees of mass discrimination or isotope separation during diffusion. The plan for testing this hypothesis includes diffusion experiments and examination of isotopic gradients around individual bubbles. The project as a whole is a combination of field effort, experiments, and theory and will push the limits of analytical and experimental capabilities. Although not stated in the objectives, the proposed measurements will help inform the next generation of volcanic conduit models and may refine techniques used for estimating the fluxes and isotopic compositions of volcanic gas species released to the Earth?s atmosphere.

火山爆发是地球上最壮观，也是最具破坏性的地质事件之一。s表面。火山爆发的爆炸性及其造成的危害取决于火山如何排出气体，或者具体地说，气泡形成的数量和速度以及从上升的岩浆中去除气体的效率。虽然存在方法来估计总气体预算的母火山岩和喷发的熔岩，这是更难得到的信息的时间和速度的泡沫增长和气体损失的岩浆向地球移动？s表面。这项研究提供了一个新的视角，专注于火山玻璃中气泡周围保存的小尺度纹理和化学梯度。该研究是基于现实的假设，缓慢的扩散可能会抑制气泡岩浆平衡，导致H2O和CO2梯度熔体。这些梯度的符号，大小和长度尺度可以使用现代分析技术进行测量，它们为理解气泡生长，再吸收和从岩浆中去除过程中分离挥发性物质及其同位素提供了新的线索。将被研究的样品包括低硅到高硅火山玻璃中的气泡和实验胶囊中生长的气泡。这项研究将主要集中在H2O和CO2的行为上，这是火山气体的两种重要成分，它们的化学扩散率不同。由于H2O具有高扩散性，其浓度分布可能会记录由于压力，温度和火山进料系统中的化学变化而导致的平衡溶解度变化。由于CO2具有低扩散性，其浓度分布可能包含有关气泡生长或再吸收和骨折愈合速率的信息。该研究还包括一种新的方法来研究熔融相化学形态和扩散之间的关系。不同的溶解物质（例如，OH和H2Om）具有不同的质量，因此在扩散过程中应表现出不同程度的质量区分或同位素分离。检验这一假设的计划包括扩散实验和检查单个气泡周围的同位素梯度。该项目作为一个整体是实地工作，实验和理论的结合，并将推动分析和实验能力的极限。虽然目标中没有说明，但拟议的测量将有助于为下一代火山管道模型提供信息，并可能改进用于估计释放到地球的火山气体种类的通量和同位素组成的技术。的大气层。