Julie Schneider, “Mica Minerals in a Ductile Shear Zone”
Mentor: Dyanna Czeck, Geosciences
Poster #118

Faults are of particular interest to geologists due to their associated earthquakes and subsequent natural disasters. The Southern Iberian Shear Zone (SISZ) in Andalucía, Spain is a ductile shear zone—a deep-seated fault which deforms rocks without fracturing, between two tectonic plates which obliquely collided. The SZIZ was specifically chosen for this study because its surrounding formations have eroded enough to expose ductile deformation at the surface. The Pulo do Lobo (PdL) formation contains sedimentary rocks which have metamorphosed into metasedimentary quartzites and slates. Analysis of mineral content and deformation in thin section samples from the PdL formation may indicate localization of strain along the fault. Localization of deformation is related to differential stress within the fault, but it is also dependent on many factors including mineral composition and distribution, differing mineral properties, and grain size. The goal of this study is to better understand why deformation localizes on the mineral-scale; in order to do so, 28 samples of rock from the PdL formation will be photographed under a microscope, then clusters of mica minerals in each sample will be traced and analyzed for percent-composition and extent of deformation. These results can then be pieced together by correlating the samples by location relative to the fault, theoretically indicating greater deformation in samples nearest to the fault with a higher- percentile mica content and/or clustering. Mica minerals were specifically chosen for analysis due to their lower threshold for deformation as opposed to quartz, the other mineral group most prevalent in the samples; thus, mica minerals are preferred for determining the rock’s degree of deformation. In theory, deformation should be most prevalent closest to the fault , while samples further from the fault will have less observable deformation and dispersed mica grains.