CO2 Diffusion in Dry and Hydrous Haplobasaltic Melts

CO2 在干燥和含水单玄武岩熔体中的扩散

• 批准号: 0838127
• 负责人: Youxue Zhang
• 金额: $ 33.02万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-15 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838127&HistoricalAwards=false
• 关键词: CO2; Diffusion; Dry; Hydrous; Haplobasaltic

Degassing during basalt eruption is the major pathway for mantle gases to enter the atmosphere and was also the major source for the formation and evolution of the early atmosphere. Carbon dioxide (CO2) is the second most abundant gas component in basaltic magmas at mid-ocean ridges and ocean islands, after water (H2O). Moreover, due to the low solubility of CO2 in melts compared to H2O, CO2 is the most major component in the gas phase during degassing of submarine basalts. Hence, bubble growth and degassing in submarine basaltic melts are largely controlled by CO2. Direct measurement of CO2 concentrations in submarine basaltic glasses often show oversaturation of CO2, meaning that basalt degassing is not an equilibrium process, but also controlled by CO2 diffusion and transport. Therefore, understanding CO2 diffusion in basaltic melt is essential to quantifying CO2 bubble growth and degassing, as well as the volatile budget of the mantle.Diffusion couple experiments will be carried out to investigate CO2 diffusion in dry and wet haplobasaltic melts. For the two halves in each couple, the chemical compositions (including H2O content) will be similar, but CO2 concentration will be zero in one half and about 1000 parts per million in the other half. The experimental procedures will be similar to our previous diffusion couple experiments on H2O and Ar diffusion. The experimental conditions will be 1300-1700°C, 0.5-1.5 GPa, and 0-7 weight% H2O. After the experiments, CO2 concentration profiles will be measured using a microscope Fourier transform infrared spectrometer. The profiles will be fit by the theoretical solution to obtain diffusivity. The new data will be combined with previous data to assess the dependence of CO2 diffusivity on temperature, pressure, and H2O content. From diffusion data obtained from this grant, bubble growth in basaltic melts will be modeled using recently developed models. Furthermore, multicomponent bubble growth will be tackled. Hence, this work will provide a fundamental understanding to CO2 diffusion, bubble growth, degassing, and kinetic fractionation of gas components of basaltic magma at mid-ocean ridge, ocean islands and island arc settings.

玄武岩喷发期间的脱气是地幔气进入大气的主要途径，也是早期大气形成和演化的主要来源。二氧化碳（CO2）是玄武岩山脊和海洋岛的玄武岩岩浆中第二大的气体成分，仅次于水（H2O）。此外，由于与H2O相比，由于CO2在熔体中的溶解度较低，因此CO2是海底玄武岩脱气过程中气相中最重要的成分。因此，海底基本熔体中的气泡生长和脱气主要由CO2控制。海底基本玻璃中二氧化碳浓度的直接测量通常显示出二氧化碳的过度饱和，这意味着玄武岩脱气不是等效的过程，而是受二氧化碳扩散和运输的控制。因此，理解玄武岩熔体中的二氧化碳扩散对于量化二氧化碳气泡的生长和脱气至关重要，以及地幔的挥发性预算。扩散夫妇实验将进行研究以研究干燥和湿的单倍乳质熔体中的二氧化碳扩散。对于每对夫妇的两半，化学成分（包括H2O含量）将是相似的，但是二氧化碳浓度在一半中为零，另一半浓度为每百万分。实验程序将类似于我们以前关于H2O和AR差异的扩散夫妇实验。实验条件将为1300-1700°C，0.5-1.5 GPA和0-7重量％H2O。实验后，将使用显微镜傅立叶变换红外光谱仪测量二氧化碳浓度曲线。理论解决方案将符合剖面，以获得难度。新数据将与先前的数据相结合，以评估CO2难度对温度，压力和H2O含量的依赖性。从从此赠款获得的扩散数据中，将使用最近开发的模型对玄武岩熔体中的气泡生长进行建模。此外，将解决多组分气泡增长。因此，这项工作将为斜山山脊，海洋岛和岛屿弧形环境的气体成分的二氧化碳扩散，气泡生长，脱气和动力学分馏提供基本理解。