Date of Award
Doctor of Philosophy (PhD)
Scott D. Samson
Appalachians, garnet, geochemistry, monazite, Provenance, zircon
Geochemistry | Geology
The provenance of clastic sediments remains one of the key tools for understanding the complex dynamic history of the Earth. Detritus shed from ancient orogens may be the only evidence available for determining the timing, evolution, paleogeography, and existence of tectonic events active over the 4.56 Ga of Earth history. The focus of this dissertation research is to assess the strengths and limitations of existing, as well as novel, tools for determining the provenance of siliciclastic sediments.
The utility of detrital monazite crystallization ages was investigated as a provenance indicator in both modern and ancient sedimentary systems. The results from these investigations show that the ages of detrital monazite record, at a higher fidelity, the complex Appalachian Paleozoic tectonic history than does detrital zircon. In several of the analyzed samples, detrital monazite recorded multiple tectonic events that were entirely missed by the detrital zircon record, thus providing a more accurate identification and assessment of sediment donor regions.
In addition, the utility of detrital garnet microchemisty was investigated as tool for quantitative sediment provenance analysis. Garnet was chemically characterized from a wide variety of lithologies that crop out within the French Broad River (western North Carolina) watershed. Mahalanobis distances measured on canonical discriminant functions successfully differentiated garnet compositions among the analyzed source rocks. These metrics successfully linked ~94% of detrital garnet compositions to the source rocks from which they were potentially derived.
Finally, bootstrapping techniques were applied to detrital zircon U-Pb ages, from two modern river systems, which allowed for the determination of statistical confidence intervals that constrained the variation in the age spectra imposed by finite sampling. The technique essentially removed that portion of the sample zircon age spectra that carries little discriminating power, thus highlighting spectral components which are unique. This approach provided a framework in which detrital zircon (or other mineral) ages can be compared and interpreted in an objective and statistically constrained context.
Hietpas, Jack, "Investigating the Utility of Detrital Mineral Microchemistry and Radiogenic Isotope Compositions as Provenance Discriminators" (2012). Earth Sciences - Dissertations. Paper 29.