T39 Sigma Gamma Epsilon Undergraduate Research (Posters)

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

GEOCHEMISTRY AND FABRIC ANALYSES OF SELECTED SHEARED GRANITIC SAMPLES FROM MOUNTAIN SHEAR ZONE, MOUNTAIN, WI

Paper number: T39-44
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Ductile deformation deep within the earth’s crust and mantle are localized within narrow bands called shear zones. These weak bands form around zones of relatively stronger rocks. The purpose of our research is to gain a better understanding of how chemistry and mineralogy might affect the strength of rocks. We conducted our research on samples collected from around the Mountain Shear Zone exposed near the town of Mountain, Wisconsin. On our sample M1002 we noticed that a shear zone defined by aligned minerals appeared to be deflected by a zone with no mineral alignment. This could be due to the presence of a stronger region deflecting the shear zone, or could be evidence of a second possible magma intrusion that occurred at the Mountain Shear Zone. The purpose of this project is to determine what caused the deflection in the fabric by comparing the geochemistry and the rock fabric at different parts of this sample. We have compared thin sections taken from different parts of the sample. We have analyzed the whole rock geochemistry of selected parts of this sample using X-Ray Fluorescence (XRF), and we are using GIS-based techniques to determine the alignment and spatial distribution patterns of minerals in different parts of the sample. The major minerals in the samples are quartz, potassium feldspar, plagioclase, biotite, and hornblende. The biotite and hornblende grains in the deformed part of the sample are aligned.

Preliminary results show that there is a slight variation between the chemistry of the deformed and undeformed parts of this sample. The undeformed parts of the sample appear to have slightly higher concentrations of ferric iron, magnesium, and calcium oxides, and slightly lower concentrations of sodium and aluminum oxides. According to the quartz + Alkali feldspar + plagioclase (QAP) diagram, different parts of the same hand sample show a range of composition varying between monzogranite and granodiorite. This observation implies that there might have been a possible episode of magma intrusion after the shearing event at the Mountain Shear Zone.

Future work on this project involves detailed mineralogical, chemical and fabric analysis of this sample and other samples collected from this location.