Crystal growth during a single-stage opening event and its implications for syntectonic veins

Abstract

The crystallization of a fluid filled vein or cavity and interpretation of the microstructure in a deformed rock is an important problem for geologists. Dynamic crystallization experiments using ice and an aqueous solution have been used as an analogue system for single-stage opening events and have shown that the presence or absence of a deviatoric stress is an important factor in the development of texture as a result of crystallization from a fluid. The textures can vary from (1) coarse crystal aggregates involving static growth where there is no significant macroscopic deviatoric stress at the time of crystallization, the free-face growth model to (2) polycrystalline aggregates involving static growth which develop from a mixture of skeletal crystals and fluid in a stressed environment. In the latter situation, the crystals and fluid coexist until the macroscopic stress can be transmitted between impinging crystals and, at this stage, fast dynamic recrystallization and grain boundary migration occurs. This recrystallization has been termed the contact growth model and the resulting metamorphic texture is compared with examples in natural quartz veins. During a single stage vein opening, uncomplicated by intragranular deformation, either free-face and/or contact growth textures can develop from the fluid filled void depending upon the kinematic environment.