T39 Sigma Gamma Epsilon Undergraduate Research (Posters)

Sunday, 9 October 2011
9:00 AM - 6:00 PM
Hall C

FABRIC AND GEOCHEMICAL CHANGES WITHIN SMALL SCALE SHEARED GRANITIC ROCKS FROM MOUNTAIN, WI

Paper number: T39-41
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Heat and pressure from tectonic forces within the Earth’s crust and mantle can create narrow ductile shear zones in rocks. The goal of our research is to get a better understanding of the effects of shear deformation on the chemistry and mineral alignment of deformed rocks. Specifically, we are trying to correlate the degree of foliation development and variation in the chemistry of sheared rocks. Our research is based on samples M0513-Q, M1001-B, M0513-O M0513-P and M0513-N, collected from around the Mountain Shear Zone in northern Wisconsin, which formed approximately 1.8 billion years ago. The samples show different stages of deformation and fabric formation despite the close proximity in which they were found. The samples M0513-O and M1001-B show little or no mineral alignment, M0513-Q shows some mineral alignment, and samples M0513-P and M0513-N show well developed alignment of biotite and hornblende grains. All samples contain quartz, plagioclase, potassium feldspar, biotite and hornblende in different proportions, except sample M1001-B, which is almost entirely made up of plagioclase and quartz. Sample M0513-Q also contains garnet crystals.

We used the Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES) at the UW-Whitewater Chemistry Department to determine the trace and Rare Earth Element (REE) concentrations in our samples. Preliminary results show a progressive increase of La, Ce, Pr, Nd, and Sm from relatively undeformed to deformed samples, while Zr remains relatively constant in all samples. The La/Sm ratio consistently increases with increasing degree of mineral alignment. We are using GIS techniques in order to quantify the fabrics so that we will be able to measure the variations in grain size and shape. We are also using X-Ray Fluorescence (XRF) for whole rock geochemical analyses, and by using X Ray Diffraction (XRD) we will be able to establish the mineral composition of the samples to find further differences between them. By employing these techniques we expect to gain a better understanding of the relationship between shear deformation and chemical changes along the Mountain Shear Zone.