5:15 PM - 6:30 PM
[SCG57-P05] Feedback among reaction, mass transport and fracturing during metamorphism: controls and and pattern formation
Keywords:reaction-transport-fracturing feedback, distinct element method, serpentinization
In this contribution, we focus on the relative rate of fluid transport and surface reaction on the fracture pattern during the volume-increasing hydration reaction. The new DEM model treats transport of water in two ways; flow along the fractures and flow through matrix. The latter has the similar effects to diffusion. For evaluate the system, we introduce two nondimensional parameters; the ratios of the rates of fracture flow (YF) and diffusion (YD) to the surface reaction rate. We found systematic changes in fracture pattern and system evolution as a function of YD and YF. In the first case that reaction is faster than water transports (YD <1 and low YF <1), the reaction proceeds from the boundaries and forms fine fractures layer-by-layer. In the second case that reaction is faster than diffusive transport of water but much slower than flow along the fracture (low YD<1 and high YF >1000), the reaction proceeds inward effectively to form hierarchical fracture networks. In the third case with high diffusion rate (YD >10), the reaction tends to proceed from the boundaries without fracturing. The dependence of the fracture pattern on YF and YD suggests the importance of the rates of water transport relative to the surface reaction rate in studying the mechanism and overall rate of water–rock reactions. The fracture pattern generated in the second case is similar to mesh texture found in the partly serpentinized peridotite in oceanic peridotites. We also discuss the effects of grain boundaries and will develop the model to more realistic reaction system which incorporate element diffusion such as silica.
Okamoto and Shimizu (2015) Earth Planet Sci Let, 417, 9-18.