David P. Moecher

Recovering tectonic events from the sedimentary record: Detrital monazite plays in high fidelity

Measurement of detrital zircon U-Pb ages has become the method of choice for single crystal–based investigations of provenance for both modern and ancient sediments. Recent studies, however, demonstrated the failure of zircon to record major tectonic events in source terranes, revealing the need for a more robust provenance methodology. A direct comparison between the utility of crystallization ages of detrital zircon and monazite as provenance indicators has been made using modern river alluvium derived from known sources. While detrital zircon does not fully record the multiple collisional phases that are the hallmark of the Appalachian orogen, detrital monazite accurately records all the major tectonic events. The physical and petrogenetic differences between zircon and monazite are the primary factors for differing detrital age spectra. Zircon, owing to its extreme refractory nature, skews detrital age spectra toward older ages and limits its ability to record low-grade thermotectonic events in orogens. Monazite recrystallizes over a broader range of metamorphic conditions than does zircon. Consequently, monazite has the potential to record metamorphic events that might otherwise be absent from the detrital zircon record, thus providing a more accurate record of source terranes in regions characterized by moderate thermal events.

Enhancing tectonic and provenance information from detrital zircon studies: assessing terrane-scale sampling and grain-scale characterization

Abstract: Determining detrital zircon U–Pb ages has become the method of choice for single- mineral-based provenance studies focused on the identification of potential source regions of siliciclastic sediments. Advances in microanalytical methods have significantly accelerated the acquisition rate of U–Pb ages, thus allowing for more statistically significant zircon age datasets to be acquired than previously. However, several studies have demonstrated limitations of relying solely on detrital zircon as a provenance proxy. To further assess the utility of this provenance indicator we measured U–Pb ages of detrital zircon derived from modern sediment collected from the French Broad River and its tributaries that drain portions of the Appalachian Orogen in southeastern USA. The results demonstrate that significant detrital zircon age variations occur along the length of the river. The age variations suggest that characterization of entire sedimentary formations by analysis of single samples may be misleading and that a multiple-sample approach is required. In addition, by incorporating high-magnification cathodoluminescence images with Th/U for each detrital grain, a more robust interpretation can be made regarding zircon source. Supplementary material: Global positioning system coordinates for each sampling location and complete zircon data are available at http:/www.geolsoc.org.uk/SUP18445.

Precise Time and Conditions of Peak Taconian Granulite Facies Metamorphism in the Southern Appalachian Orogen, U.S.A., with Implications for Zircon Behavior during Crustal Melting Events

The time of peak thermal conditions in the granulite facies zone of the southern Appalachian orogen corresponds to the time of formation of garnet‐bearing leucosomes generated by biotite dehydration melting in garnet‐sillimanite gneisses. Leucosomes contain unusually abundant zircon occurring as inclusions in euhedral plagioclase phenocrysts and garnet. Isotope dilution thermal‐ionization mass spectrometric analysis of 13 elongate, euhedral zircon crystals from the leucosome yields a concordant U‐Pb age of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Extraction and carbon isotope analysis of CO2 from scapolite in deep crustal granulites and xenoliths

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Brecciated and mineralized coals in Union County, Western Kentucky coal field

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The Effect of Deformation on Oxygen Isotope Exchange in Quartz and Feldspar and the Significance of Isotopic Temperatures in Mylonites

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