Document Type
Thesis
Abstract
The Goochland Terrane is an isolated block of Mesoproterozoic crust in the Piedmont province of Virginia. Four principal units constitute this terrane: the State Farm gneiss, Sabot amphibolite, Montpelier anorthosite, and Maidens gneiss (Farrar, 1984). Recent work by Owens and Tucker (in press) has also shown that the State Farm gneiss was intruded by numerous granites in the Neoproterozoic (~600 Ma). These Neoproterozoic rocks can be classified so-called “A-type” granites, in which the “A” stands for anorogenic or alkaline. A-type granites have distinct chemical compositions, which allow them to be distinguished from other granite types (e.g. Whalen et al., 1987). Models developed for the origin of A-type are not wholly conclusive and include: fractionation of mantle derived basaltic magma, late stage alkali-, F-, or Cl-rich solutions interacting with residual magma or metasomatically with older granites, and melting of high grade felsic metamorphic rocks from which a previous melt phase had been extracted (Eby, 1990). The Neoproterozoic A-type granites were interpreted by Owens and Tucker (in press) to reflect Neoproterozoic rifting of the Goochland Terrane. As such, these granites are similar to those of the Robertson River Igneous Suite in the Blue Ridge province of Virginia, which have also been interpreted as rift-related (Tollo and Aleinikoff, 1996). Thus far, Neoproterozoic granites have only been recognized within the main State Farm gneiss dome. However, numerous bodies of granitic gneiss have been recognized to the west within the Maidens gneiss (Virginia Department of Mineral Resources, 1993; Marr, 1998; Bobyarchick et al., 1981; Crawford, 2001) that possibly represent additional examples of Neoproterozoic magmatism. The objective of this study was to investigate the mineralogy and chemical compositions of several of these granitic units, and to test the hypothesis that they are Neoproterozoic based on correlations with known occurrences recognized by Owens and Tucker (in press).
Date Awarded
2003
Department
Geology
Advisor 1
Brent E. Owens
Recommended Citation
Rossi, Matthew, "Evaluation of the Extent of Neoproterozoic Magmatism in the Western Goochland Terrane, Piedmont Province, Virginia" (2003). Geology Senior Theses. William & Mary. Paper 120.
https://scholarworks.wm.edu/geologyseniors/120
