Dulce Hernandez-Blanchard, “Microstructural Observations Across the Southern Iberian Shear Zone”
Mentor: Dyanna Czeck, Geosciences
The interactions of tectonic plates cause deformation in rocks that result in a shear zone. A shear zone is a tabular zone of rocks that has measurable thickness in which strain is localized when two sections of rock smear against each other. Water and other fluids can change the deformation style of shear zones, strongly influencing the heterogeneity of deformation in the Earth’s crust. For this study, I am contributing to ongoing research on the interactions of fluids and deformation in the Southern Iberian Shear Zone (SISZ) located in Southern Spain. To analyze the Acebuches Metabasites, seven thin section samples that spanned the Calabazares transect were observed using a petrographic microscope, and observations of mineralogy were made which concluded that amphibole, plagioclase, and pyroxene were abundant within the samples. After observing the mineralogy, two different types of microstructures were considered; solution seams and veins and their relationship with the mineral content and angle against foliation. Microstructures such as solution seams occur when a liquid or gas diffuses down the concentration gradient which causes diffusional mass transfer (DMT) which is the dominant deformation mechanism in the upper and middle crust. We found that the veins composed of plagioclase and amphibole minerals were nearly all perpendicular to the foliation; however, there was no correlation between the orientation of solution seams and microfractures, but the presence of solution seams and microfractures provides evidence of fluid interaction during deformation. Researching the mineralogy and microstructures more at depth will help future research in determining how fluids play a major role in controlling the metamorphic reactions and deformation style of this shear zone.