Effects of annealing on deformation textures in galena

Abstract

Experimental annealing of galena samples with known deformation histories shows that this mineral has the necessary properties to be a valuable source of information about low-grade deformational environments. Annealed galena displays recovery and/or recrystallization features dependent upon the type of texture inherited from the tectonic event, which in turn is closely linked to deformation temperatures.

In samples deformed at temperatures less than 200 ° C in the laboratory, later annealing produced subgrains, mosaics of new grains, or rapid grain boundary migration as the annealing temperatures were varied from 200 ° C to 700 ° C. Kink bands maintained characteristic straight simple boundaries inherited from the deformation event. Samples deformed above 300 ° C developed “syntectonically” recrystallized textures. Kink bands had been converted to elongate grains with complex sutured grain boundaries during deformation, and mosaics of new grains were found in highly deformed regions. These textures were extremely stable through later annealing. Despite our changing annealing temperatures through 500 ° C, we did not produce similar textures from both low and high temperature deformation runs.

Examination of polished and etched galena from low-grade tectonic settings may well be worth the effort since galena textures appear to display features indicative of deformational evironments, even after being subjected to considerable post-tectonic thermal perturbations.