Alteration of basalt mineral surfaces at hydrothermal conditions: Insights into reaction mechanics during solid-fluid interactions.

The analysis of solid-fluid interactions in nature is crucial for our understanding of material fluxes and sub-surface stability. However, there is still a significant quantitative and qualitative difference between dissolution data obtained in nature and laboratories. With modern surface-analysis techniques like AFM, VSI, SEM and Raman Spectroscopy, we can observe alteration on mineral surfaces on a high nanometer to low micrometer scale. This enables us to figure out microscopic reactions that can lead to macroscopic changes at rock surfaces. To gain insights into a natural basaltic system, a subsurface observatory has been installed in a borehole at Surtsey volcano off the southwest coast of Iceland a. In the observatory, mineral surfaces of olivine (Fo90) and basaltic tephra were exposed to hydrothermal conditions at 41°C and 96°C respectively.

Laboratory experiments were performed with the same material under conditions similar to those in the Surtsey borehole. With the help of data from both experimental studies, we examined different gradients of palagonization reactions at glass surfaces as well as a beginning serpentinization of olivine at high temperature conditions. At low temperatures, especially olivine surfaces examined etch pits as a result of dissolution reactions. These differences in surface alteration demonstrate the complexity and the influence of various mechanics that play a role at solid fluid reactions and surface alteration. Furthermore, ongoing experiments address the role of microbe-mineral interactions in controlling the rates and mechanisms of mineral dissolution and precipitation.

a Türke et. al.: Design of the subsurface observatory at Surtsey volcano, Iceland, 2017.