Document Type
Thesis
Abstract
The Moseley felsic gneiss is an enigmatic unit within the Goochland Terrane of Virginia. It is found along the Hylas fault west of Richmond and just north of Moseley, Virginia, and southwest of the State Farm gneiss. Previously, the Moseley felsic gneiss has been variously interpreted as a granite, mylonite, or felsic metavolcanic rock. Results of this study show that the Moseley felsic gneiss is not mylonitic everywhere, but is typically fine-grained. The gneiss casually resembles the Neoproterozoic granitoids related to rifting found within the State Farm gneiss (e.g. Fine Creek Mills and Flat Rock granites). However, results from modal and chemical analyses reveal that this resemblance is limited to the unit’s physical appearance. Modally, the Moseley felsic gneiss ranges from tonalite to granodiorite. It is peraluminous and contains almost abnormally high SiO», low to trace amounts of K2O, and low Fe and Mg, but a high Fe/Mg ratio. The unit has a low Ga/AI ratio and plots in the I-, S-, and M- type granite field. On an An-Ab-Or ternary diagram, the Moseley felsic gneiss plots in the trondhjemite field. In a Rb vs. (Y + Nb) discrimination diagram, the unit plots in and close to the volcanic arc granite (VAG) field. All of these features are unlike those of the Neoproterozoic granitoids, suggesting that the Moseley felsic gneiss is not related to them. Field relations, mineralogy, and chemical compositions indicate that the Moseley felsic gneiss probably represents a metamorphosed volcanic rock—possibly a trondhjemite from a volcanic arc setting related to subduction.
Date Awarded
2003
Department
Geology
Advisor 1
Brent E. Owens
Recommended Citation
Burnett, Kimberly A., "Mineralogical and Geochemical COnstraints of the Moseley felsic gneiss, Goochland Terrane, Virginia" (2003). Geology Senior Theses. William & Mary. Paper 110.
https://scholarworks.wm.edu/geologyseniors/110
