FluidNET abstract GMDM - Factors controlling replacement reaction front patterns in fluid-rock interactions

Factors controlling replacement reaction front patterns in fluid-rock interactions Lorena H. Filiberto1*, Christine V. Putnis1,2 1Institut für Mineralogie, University of Münster, 48149 Münster, Germany 2School of Molecular and Life Sciences, Curtin University, Perth, 6845, Australia Experiments on simulating hydrothermal conditions during fluid-rock interactions to achieve mineral replacement reactions have been often reported in the literature. Most of these experiments are conducted using single mineral grains where the replacement occurs from the rim of the grain towards the core, but when we use rock samples instead of single crystals, where grain boundaries and fractures exist, we see that the replacement reaction front occurs in two main different ways: either the product phase replaces the parent phase from the edges of the sample, that is the part of the rock that is first in contact with the fluid; or the replacement proceeds through the grain boundaries and the sides of the grains exposed to the outer solution often appear less reacted. These different types of reaction front patterns can be seen in many geological settings, from a micron to a meter scale. To try to determine which factors influence whether the reaction progresses in one way or another, we performed a series of hydrothermal experiments at 200°C using monomineralic rocks and various types of solutions. For example, when an artificial seawater solution reacts with a Carrara Marble sample, composed of calcite grains, the first type of reaction front mentioned above occurs: a magnesite phase replaces the calcite grains from the sample's edge, and the majority of the grain boundaries away from the edge appear unreacted. However, when the same type of sample is reacted with a phosphate solution, a Ca-phosphate phase replaces the calcite through the grain boundaries, as described in the second type of reaction front pattern. Here we present our findings from analyzing the rock samples and fluids used in these experiments with SEM coupled with EDX, Electron Microprobe, ICP-OES, and Raman to identify the potential parameters involved in this phenomenon