Grain boundaries as reactive fluid pathways in rocks

The presence of aqueous fluids is ubiquitous in the Earth’s crust. Grain boundaries play an important role in enabling fluids to penetrate through the rock system. Their influence in fluid-rock reactions that might lead to relevant processes such as mineral replacements, the formation of new minerals and dissolution of others, element mobilization, variations in rock density, changes in stress distribution, mass transfer, etc., are commonly observed in many rock samples as well as generated and observed in laboratory experiments. As a product of these reactions, porosity and fractures might also be generated and potentially allow the fluid to penetrate even further.

Here we present our first analyses on different rock samples where the fluid-rock interaction has been induced through hydrothermal laboratory experiments using either Carrara Marble or plagioclase samples. The evidence for such interactions having previously occurred in natural rocks has been investigated in a sequence of a granulite rock samples from the Bergen Arcs in Norway. Using light microscopy as well as SEM, EDX and Electron Microprobe analysis we have investigated possible fluid pathways and evidence of fluid-mineral reactions as well as the mechanisms that could explain such processes.