Feedback Mechanisms Between Weathering Advancement and Cohesive Fracture Propagation in Granite

Abstract

Biotite weathering in granite is known to induce micro-crack propagation. Conversely, fracture propagation exposes fresh surfaces to percolating fluids and enhances fluid flow, which accelerates chemical weathering. These feedback mechanisms between weathering, microcracks and larger fractures remain under-explored. To bridge this gap, a weathering-induced damage model is coupled with a cohesive fracture model to study the joint effects of topographic, tectonic, and weathering stresses in granite. Weathering is simulated over 250 years in sinusoidal topographies. Numerical results suggest that without pre-fracturing, horizontal tectonic stresses are needed to trigger weathering. Under tensile horizontal tectonic stress, simulations indicate that weathering advances vertically beneath the valleys, consistent with field observations. The model predicts that where compressive tectonic stresses are transmitted beneath and parallel to valley bottoms and side slopes, surface-parallel fracturing is promoted, and weathering regions spread laterally beneath both the valleys and ridges, in conformity with fractures observed parallel to and subparallel to the surface. Simulations also indicate that the stress concentrations beneath a valley promotes mode-I fracture propagation where the horizontal tectonic stress is tensile, but does not significantly impact mixed-mode fracture propagation subparallel to the surface where the horizontal tectonic stress is compressive.