Incomplete Crack Sealing Causes Localization of Fracturing in Hydrothermal Quartz Veins

Abstract

Cyclic microfracturing and epitaxial crystal growth have long been recognized in crack-seal veins, but an understanding of a single crack-seal cycle is still missing. Here we present a phase-field model that includes both fracture mechanics of crack propagation, and epitaxial crystal growth on the fracture walls, repeating this cycle multiple times in a polycrystalline, microporous quartz rock. Our simulations have two end members: If a vein completely seals, it is stronger than the host rock, cracking is delocalized, forming many single-seal microveins. Incomplete sealing makes the vein weaker than the host rock and localizes the new fracture inside the vein, leading to multi-crack-seal. We suggest that the sealing degree is a key parameter in hydrothermal systems and multi-crack-seal veins are long-lived, microporous sites of mechanical weakness. We generalize the phase-field approach to conduct probabilistic simulations in between these two types, and show how systems of microveins and multi-crack-seal veins emerge.