16-50 Geochemistry of Granitic Pegmatites of Chester County, Pennsylvania

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

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Abstract:

Geochemical characterization of granitic pegmatites in Chester County, Pennsylvania provide a gateway into understanding their origin. Fieldwork and sample collection was completed at two localities: Elk Creek and Coatesville, Chester County, PA. Located in the Piedmont Province, the Elk Creek pegmatite intrudes the Paleozoic Wissahickon schist, whereas the Coatesville pegmatite intrudes the Precambrian Baltimore gneiss. Granitic pegmatites can form through a variety of tectonomagmatic processes, including (but not limited to): arc-related magmatism, syn-collisional anatexis, and delamination-induced extension. Each process will impart a distinct geochemical signature that will reflect the magmatic source. Six representative samples, three from each locality, were selected for major, minor, and trace element geochemical analysis. Element concentrations and mineralogy are consistent with an NYF (niobium-yttrium-fluorine) muscovite rare earth element (REE) pegmatite, corresponding with anorogenic or A-type granites. Data plotted on petrogenetic discrimination diagrams did not reveal consistent trends. Most data plot within the volcanic arc granite (VAG) field, however, some plot in the syn-collisional (syn-COL) and within-plate granite (WPG) fields. Chondrite-normalized REE patterns display a negative trending slope. Samples with the greatest REE enrichment exhibit pronounced negative Eu anomalies, consistent with a highly evolved melt. The results suggest an evolved felsic melt forming from either arc-related, anorogenic, or mixed processes. The results highlight the complex tectonomagmatic processes that influenced pegmatite formation within Chester County, Pennsylvania. 

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