Lewis, David John (2015-12). Detrital Zircon Trace Element Characterization of Middle to Late Ordovician Quartz Arenites along the Transcontinental Arch. Master's Thesis.
During the Middle to Late Ordovician, Laurentia was situated over the equator and the Transcontinental Arch, and its exposed basement rock and sedimentary cover straddled the equator. This resulted in unique siliciclastic deposition of a diachronous group of quartz arenites during an otherwise long interval of almost entirely carbonate deposition. In recent years, a rapidly expanding database, especially in laser ablation - inductively coupled plasma mass spectrometry (LA-ICPMS) geochronology, has led to significant advances in understanding the provenance of these quartz arenites on both sides of the Transcontinental Arch, the passive margin of western Laurentia and US Midcontinent. Detrital zircon from quartz arenite samples were previously dated using U-Pb methods to make interpretive correlations between detrital zircons and their source terranes. However, age data alone do not always uniquely discriminate between potential source regions. To aid in further discrimination, an LA-ICPMS analytical method was developed to obtain trace-elemental composition data from detrital zircons that were previously analyzed for U-Pb ages. When coupled with U-Pb geochronologic data, this additional geochemical data can serve as an improved reference for discrimination between source terranes. Trace element diagrams (e.g. REE plots) are used as discrimination diagrams to differentiate between potential source regions that are of similar age. Results of this study indicate that there are no significant resolvable differences in zircon trace element compositions that can be correlated with differences in U-Pb age spectra from the quartz arenite samples.