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.

玄武岩喷发过程中的脱气是地幔气体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）是大洋玄武岩岩浆中第二丰富的气体成分。此外，由于 CO2 在熔体中的溶解度低于 H2O，因此 CO2 是潜艇脱气过程中气相中最主要的成分。因此，海底玄武岩熔体中的气泡生长和脱气很大程度上受 CO2 控制，直接测量海底玄武岩玻璃中的 CO2 浓度通常会显示 CO2 过饱和，这意味着玄武岩脱气不是一个平衡过程，而且还受到 CO2 扩散和控制。因此，了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以及地幔的挥发预算至关重要。将进行扩散偶实验来研究二氧化碳的扩散。在干和湿的单玄武岩熔体中，每对的两半的化学成分（包括 H2O 含量）相似，但其中一半的 CO2 浓度为零，另一半的 CO2 浓度约为百万分之 1000。与我们之前关于 H2O 和 Ar 扩散的扩散偶实验类似，实验条件为 1300-1700°C、0.5-1.5 GPa 和 0-7 重量%。实验结束后，将使用显微镜傅里叶变换红外光谱仪测量 CO2 浓度分布，该分布将通过理论解决方案进行拟合以获得扩散率，以评估 CO2 扩散率的依赖性。根据本次资助获得的扩散数据，将使用最近开发的模型对气泡生长进行建模。此外，还将解决多组分气泡生长问题。对大洋中脊、海洋岛屿和岛弧环境中玄武岩浆气体成分的二氧化碳扩散、气泡生长、脱气和动力学分馏有基本的了解。