T258 Sigma Gamma Epsilon Undergraduate Research (Posters)

Wednesday, 21 October 2009
9:00 AM - 6:00 PM
Hall A

MAFIC MICROGRANULAR ENCLAVES WITHIN SHEARED GRANITIC ROCKS IN MOUNTAIN, WI

Paper number: T258-44
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Granitic plutons are commonly associated with enclaves either in the form of xenoliths or as mafic inclusions. Such enclaves can provide significant clues about the intrusive history of the granitic pluton. Abundant mafic microgranular enclaves (or MMEs) are present within a granitic body exposed in and around the Mountain Shear Zone near the township of Mountain, Oconto County, Northern Wisconsin. Previous researchers concluded that these rocks belong to the eastern part of the Pembine-Wausau Terrane which was accreted to the Superior craton during the Penokean Orogeny about 1,860-1,889 Ma ago. It has been claimed that the enclaves resulted when the studied granitic plutonic body intruded nearby mafic and felsic volcanic rocks. Both the mafic lava flow and the granitic pluton were later deformed by ductile shearing, forming amphibole schist and granitic gneiss respectively. We have observed MMEs within both the undeformed granitic protolith and its deformed counterpart.

We have samples that are part of relatively undeformed large (10-100 meter scale) mafic enclaves within outcrops of highly deformed granitic rocks, which at times cuts across small scale ductile shear zones within granitic rock. Such field relationship might indicate that at least some of those mafic bodies might have intruded the region after the shearing event.

In the Poster we will be present the location map of the field area from where we collected the MME samples and describe their mineralogical, chemical and grain size characteristics based upon petrographic and X-Ray diffraction(XRD) analyses. Future work will involve preparing a detailed map of the larger mafic enclaves in a few of the outcrops within deformed and undeformed granitic rocks and attempt to determine their spatial distribution characteristics with respect to the Mountain Shear Zone using GIS and GPS technologies. We will also conduct further detailed mineralogical analyses using petrographic microscopes and XRD, and chemical analyses using X-ray fluorescence (XRF) to compare different MME samples.