CO2 Diffusion in Dry and Hydrous Haplobasaltic Melts

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

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.