The recognition of quartz grown from a melt during static and dynamic conditions
thesisposted on 2022-03-28, 23:41 authored by Joyjit Dey
Quartz microstructures are routinely used to establish the nature of solid-state deformation mechanisms. However, it is unclear which microstructures are typically developed in a melt present environment compared to a solid state, and how to distinguish between these two. The microstructural features of quartz crystallising from a silicate melt are investigated in a) slowly cooled granite, b-c) statically heated and cooled, and actively deforming migmatites, and d) in a melt-fluxed high strain zone. This study takes a holistic approach integrating microscopic observation along with electron back scatter diffraction (EBSD) and weighted burgers vector (WBV) analysis. Results show quartz pseudomorphing melts pockets forms sub-grain boundaries and shows crystal bending, and change in orientation very similar to a solid-state deformaion. EBSD and WBV analyses identify dislocations on both basal plane and non-basal plane, and identify slip and [c] slip, and sometimes a combination of both. Existence of slip-systems, though without a crystallographic preferred orientation (CPO), suggests the features are dependent on local stresses rather than regional differential stress, and are interpreted to be a result of mineral growth in pore spaces when the melt crystallises. Differences to solid-state deformation microstructures include well connected grains in 3D, lack of CPO, lack of grain shape preferred orientation, and high dauphine twin frequency at grain boundaries.