CO2 Diffusion in Dry and Hydrous Haplobasaltic Melts

玄武岩喷发脱气是地幔气体进入大气的主要通道，也是早期大气形成和演化的主要来源。 二氧化碳（CO2）是大洋中脊和洋岛玄武岩岩浆中含量第二高的气体成分，仅次于水（H2O）。 此外，由于与H2O相比，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主要的组分。 因此，气泡的生长和海底玄武岩熔体中的脱气在很大程度上控制CO2。 直接测量海底玄武岩玻璃中的CO2浓度往往显示CO2过饱和，这意味着玄武岩脱气不是一个平衡过程，而是受CO2扩散和传输控制。 因此，了解CO2在玄武岩熔体中的扩散是必不可少的量化CO2气泡的生长和脱气，以及地幔的挥发性budgets.Diffusion耦合实验将进行研究CO2在干和湿的haplobasaltic熔体的扩散。 对于每对中的两半，化学成分（包括H2O含量）将相似，但一半的CO2浓度为零，另一半约为百万分之1000。 实验程序将类似于我们以前的扩散对H2O和Ar扩散的实验。 实验条件为1300-1700°C、0.5-1.5 GPa和0-7重量% H2O。 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。 将通过理论解拟合曲线以获得扩散率。 新数据将与以前的数据相结合，以评估CO2扩散率对温度，压力和H2O含量的依赖性。 从扩散获得的数据，从这个补助金，玄武岩熔体中的气泡生长将使用最近开发的模型建模。 此外，将解决多组分气泡生长问题。 因此，这项工作将提供一个基本的了解CO2扩散，气泡生长，脱气，和动力学分馏的玄武岩岩浆在洋中脊，海洋岛屿和岛弧设置的气体组分。

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.