The goal of the National Science Foundation (NSF) Research Experience for Undergraduates (REU) 2000 research team internship was to attempt to understand further the nature of the Carroll Knob rock complex in the Western North Carolina mountains. Field and petrologic investigations focused on two small areas, Carroll Knob and Jones Creek, in which four distinct mappable mafic/ultramafic lithologies were indentified. Locating, describing, and identifying the units involved not only initial field investigations, but subsequent thin section and geochemical analysis.
Metamorphism due to ancient orogenic events has altered most of the rocks in this region, producing metadunite, metapyroxenite, metagabbro, and amphibolite, among other local lithologies. The mineralogical evidence for dominant mid- to upper- amphibolite facies metamorphic conditions includes the presence of particular mineral assemblages. Geochemical samples from the field areas prepared for DC plasma emission spectrometry (DCP) yielded major and trace element compositions for the rocks. These data were then plotted against known compositions of other mafic/ultramafic rocks so as to ascertain possible origins. Our data generally support the accepted hypothesis that the mafic/ultramafic rocks in the region represent cumulate sequences. However, the available data leave unclear the tectonic environments in which these units developed and were emplaced.
Metamorphism also has produced complicated structures throughout the region. The ultramafic units generally form elongate, NE-trending, foliation-parallel lenses within the dominant amphibole, which follows the tight, steeply-inclined, post-emplacement folding. The REU 2000 team brought in geophysical equipment to attempt to better elucidate the geometry and extent of the ultramafic bodies in relation to the mafics. Our “runs” included seismology, resistivity, conductivity, magnetometry, Ground Penetrating Radar (GPR), and Global Positioning Systems (GPS). We determined that, while geophysics is valuable in some regions, the complex structure of our area limits the benefits to only certain analyses.
Jennifer Natoli, ’01 San Angelo, TX
Major: Geology, Minor: English
Sponsor: Paul L. Garvin