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Dissertation/Thesis Abstract

Elemental, isotopic, and particle fingerprinting of dust sources in the San Francisco Peaks, Arizona
by Saad, Emily M., M.S., Northern Arizona University, 2013, 98; 1537808
Abstract (Summary)

This study examines dust in the San Francisco Peaks located on the Colorado Plateau of northern Arizona, USA. Sample dusts were collected from potholes on Humphreys Peak (35o20'22"N, 111o41'42"W) in order to detect exogenous material and constrain dust sources. Bulk dust and local rock were characterized by Sr and Nd isotope fingerprints as well as elemental composition. Sr and Nd isotope ratios were analyzed by MC-ICP-MS; trace element concentrations were analyzed by Q-ICP-MS. Mineralogical analyses were also performed in an effort to characterize individual particles. Mineral grains were separated from bulk samples by conventional heavy mineral separations. The heavy fraction was imaged and characterized by SEM/EDX.

Both the isotopic and elemental bulk analyses indicated that the dust composition reflected not only a weathered local rock material but also exogenous material of continental crust origin. The dust was characterized by an average 87Sr/86Sr ratio of 0.7095 ± 0.0010 and an average ε Nd of -7.13 ± 0.97. These signatures systematically and significantly deviate from the isotope fingerprints of the local rock, which exhibited an average 87Sr/86Sr ratio of 0.7037 ± 0.0002 and an average εNd of -2.43 ± 0.43. The negative correlation between εNd and 87Sr/86Sr is consistent with two component mixing of rock evolved from a mantle source and continental crust derived material.

Several geologically relevant trace elements were found to have significantly different average concentrations in the dust than in the local rock samples. Furthermore, the elemental abundances of most elements in the dust samples suggested a mixture of local rock and continental crust end members with the exception of Pb, which indicated an anthropogenic influence exhibiting enrichment factors between 1.65 and 7.44.

The mineral analysis provided further evidence of exogenous material and offered the opportunity for further constraint of the sources. Zircons were identified only in the dust and will be analyzed for U-Pb signatures in order to characterize the isotopic fingerprint of individual mineral grains, which will better distinguish external sources. Diatom skeletons were also found exclusively in the dust samples and offer a unique opportunity to more specifically implicate sources through a diatom assemblage.

Indexing (document details)
Advisor: Ketterer, Michael E.
Commitee: Ingram, Jani C., Reid, Mary R.
School: Northern Arizona University
Department: Chemistry and Biochemistry
School Location: United States -- Arizona
Source: MAI 51/06M(E), Masters Abstracts International
Subjects: Analytical chemistry, Environmental science, Geochemistry
Keywords: Dust provenance, Isotope geochemistry, Zircon provenance
Publication Number: 1537808
ISBN: 978-1-303-09688-4
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