Document Type
Thesis
Abstract
The Raleigh terrane is a high-grade basement terrane located in the Piedmont provinces of Virginia and North Carolina. It is composed predominantly of gneiss and schist in the middle to upper amphibolite facies, and many areas show evidence of intense deformation and retrograde deformation. It has been argued that due to similar metamorphic facies, the Raleigh terrane is a southerly extension of the Goochland terrane (Farrar, 1984). This study examined Raleigh terrane gneiss in and around the Lucky Lake Gem Mine in an effort to (1) evaluate its extent and homogeneity; (2) ascertain a protolith based on whole-rock chemical compositions; (3) determine if trace elements can be used to constrain the gneiss’ original tectonic setting; (4) reveal any key similarities or differences between gneiss in the Raleigh terrane and the Maidens gneiss of the Goochland terrane; and (5) determine whether these rocks are good candidates for zircon geochronology. 12 samples were collected from Lucky Lake and the surrounding areas of Lake Rawlings and Beaver Pond Creek. Field observations, petrography, and chemical composition data were used to determine that gneiss in Lucky Lake and gneiss in the surrounding field area represent two distinct units. Gneisses from Lucky Lake are intermediate in composition, and classification schemes indicate a dioritic to quartz monzodioritic protolith. Gneisses from Lake Rawlings and Beaver Pond Creek are felsic, and have a broadly granitic protolith. Tectonic discriminant diagrams, along with the gneiss’ medium to coarse grain size, suggest the gneisses were formed by subduction-zone plutonism. Geochemical similarities exist between gneisses from this study and samples of the Maidens gneiss from Hancox (2011), but different mineral assemblages preclude any definite relationship between the Raleigh and Goochland terranes. High Zr levels and an abundance of igneous zircons suggest that samples from this study are good candidates for zircon geochronology.
Date Awarded
2014
Department
Geology
Advisor 1
Brent E. Owens
Recommended Citation
Adler, Samuel Louis, "Mineralogy and Geochemistry of Gneisses in the Vicinity of the Lucky Lake Gem Mine, Raleigh Terrane, Virginia" (2014). Geology Senior Theses. William & Mary. Paper 302.
https://scholarworks.wm.edu/geologyseniors/302
