Sheared-bedding parallel quartz vein as an indicator of deformation processes

Monomineralic veins are well known as good recording of filling and precipitation processes. However, they are also able to register the action of deformation in rocks. We used monomineralic, quartz veins from Quadriláterro Ferrífero, Brazil, to represent how the deformation actuated during the transformation of different structures. They were analyzed using a combination of a u-stage and EBSD. Two main types of quartz aggregates are distinguished: single crystals with subgrain development and strain-free grains of quartz. We interpret the microstructures and textures as the result of a combination of concurrent crystal plasticity, microfracturing, solution transfer and recrystallization. The single quartz grains were deformed by dislocation glide. However, as the c-axis orientation of the grain was not favorable for further glide on basal planes, the deformation was accommodated by microfracturing. New grains were formed along the deformed zones with crystallographic orientations suitable for gliding on basal planes. As the deformation proceeded, the new grains continue to develop until the vein was completely recrystallized into an aggregate of granular grains.

► Quartz veins from Quadrilátero Ferrífero, Brazil were analyzed by u-stage and EBSD.
► Quartz grains are deformed by crystal plasticity and microfracturing.
► Monocrystalline veins evolve to a polycrystalline aggregate.
► Dauphiné twinning can activate the microshearing of quartz.
► Fluid activity can change the basal slip system of quartz to prismatic.