Date of Award

12-2012

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Daniel Lux

Second Committee Member

Alice Kelley

Third Committee Member

Brian Robinson

Abstract

Sample rhyolites from two volcanic centers (Traveler and Kineo) of the Devonian-age Piscataquis Volcanic Belt have distinctive hand specimen, geochemical, and mineralogical characteristics. Petrographic analysis shows mineralogic variability between these geographically separated centers. Thin sections of two Traveler rhyolite samples (KT-79-11, KT-163) have a quartz free groundmass and pyroxene phenocrysts that are not found within any of the Kineo sample thin sections. Electron microprobe analysis of plagioclase also displays higher anorthite concentrations—in the range of andesine and labradorite- in sections KT-79-11, and KT-163. All other sections display feldspars with end-member albite compositions, and allow discrimination between samples of the Traveler and Kineo volcanic centers. Geochemical distinctions between the samples are observable on major element Harker diagrams, as well as Zr and TiC>2 concentrations. Whole rock characterization can be useful in archaeology in distinguishing the provenance of lithic artifacts. Energy dispersive x-ray fluorescence (ED-XRF) and wavelength dispersive x-ray fluorescence (WD-XRF) analysis suggests one artifact classified as Kineo-like in earlier work may be sourced from the Traveler volcanic center (MAK-171). All other artifacts, analyzed with ED-XRF (n = 5), plot in the compositional range of geological samples from the Kineo center. ED-XRF analyses were conducted on a Bruker Portable XRF (P-XRF), while WD-XRF analyses were conducted on a Bruker Pioneer S4™. Samples analyzed by the P-XRF (non-destructive) and WD-XRF (destructive) methods share similar results. Precisions and uncertainties produced from P- XRF (ED) analysis show that the WD-XRF method is much more precise with a higher limit of detection for elements of interest. P-XRF (ED), despite large uncertainties, was capable of resolving geochemical differences between rock samples of the Kineo and Traveler center. ED-XRF and WD-XRF methods produced geochemical data that was qualitatively comparable through examining energy counts (ED-XRF) to weight percentages and part per million concentrations (WD-XRF). Data obtained using the P- XRF displayed high RSD (Relative Standard Deviation), with a minimum of 6%, and a maximum nearing 20% for elements of interest. These values, though quite large, still allow for a semi-quantitative non-destructive assignment of their provenance.

Download

Files over 10MB may be slow to open. For best results, right-click and select "save as..."

Share