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.

火山喷发是地球表面上最壮观，可能是毁灭性的地质事件之一。火山喷发及其构成的危害的爆炸性取决于火山的爆发，特别是尤其是气泡形成的数量和速率以及从上升的岩浆中清除气体的效率。尽管存在估计父母和熔岩爆发的总气体预算的方法，但是随着岩浆向地球的表面移动，很难获取有关气泡生长和气体损失的信息和气体损失的信息。这项研究通过专注于在火山玻璃中的气泡周围保存的小规模质地和化学梯度来提供新的视角。该研究基于这样的现实假设，即缓慢的扩散可能抑制气泡麦克马平衡，从而导致熔体中的H2O和CO2梯度。可以使用现代分析技术来测量这些梯度的符号，大小和长度，并为理解负责分离挥发性物种及其同位素的过程提供了新的线索，在气泡生长，吸收和从MAGMA中删除过程中。将研究的样品包括在实验胶囊中生长的低至高硅玻璃玻璃和气泡中的气泡。这项研究将主要集中在H2O和CO2的行为上，H2O和CO2是火山气体的两个重要组成部分，其化学扩散性不同。由于H2O具有较高的扩散率，因此由于压力，温度和化学变化，其浓度曲线可能会记录火山馈线系统中的平衡溶解度的变化。由于CO2的扩散率较低，因此其浓度曲线可能包含有关气泡生长或吸收率和断裂愈合率的信息。该研究还包括一种新的方法，用于研究化学物种形成与熔体相位的扩散之间的关系。不同的溶解物种（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歧视或同位素分离。测试该假设的计划包括扩散实验和检查各个气泡周围的同位素梯度。整个项目是现场努力，实验和理论的结合，并将推动分析和实验能力的限制。尽管没有在目标中陈述，但提出的测量结果将有助于告知下一代火山导管模型，并可能优化用于估算释放到地球大气层的火山气体的通量和同位素组成。