Numerical simulations of polycrystal growth in veins

摘要

Vein microstructures contain a wealth of information on conditions during vein growth but correct interpretation requires an improved understanding of the processes involved. In this paper we investigate the parameters controlling vein microstructures using numerical simulations of anisotropic crystal growth. We focus on the effects of crystal growth rate anisotropy on growth competition and on the effects of the wall rock on vein microstructure during crack-seal growth. Growth competition in a free fluid is controlled by the crystallographic orientation and growth anisotropy of the crystals. We discuss the merits and limitations of different algorithms to simulate free growth in veins, based on a detailed study of the crystal facets and grain boundaries produced. Microstructures in crack-seal veins are influenced by additional parameters, such as the width of individual crack-seal increments and the fracture morphology. We present a detailed study of the transition between free-fluid growth and crack-seal growth as a function of the relative rates of crack opening and crystal growth, to illustrate how this induces the microstructural transition between fibrous and blocky veins.