Document Type
Thesis
Abstract
The Lawrenceville granite pluton, located immediately southwest of Lawrenceville, Brunswick County, Virginia, is bounded in the east by the Hollister Shear zone, comprised of phyllonites. Near this contact, andalusite-bearing schists form a ~0.25 km wide band between the granite and phyllonites in two distinct locations trending north-south along the contact. The rocks apparently contain no cordierite or staurolite, implying that the pressure and temperature of the metamorphic event was ~2.5 kbars and between 530-600°C, based on published phase equilibria. This pressure corresponds to a depth of ~7.5 km. Retrogression of the andalusite implies that a second metamorphic event occurred after initial crystallization. Ages for monazite crystallization in the schists obtained using the Th-U-total Pb chemical dating method on an electron microprobe gave one reliable age population at ~444 Ma, and a smaller, less reliable, peak at ~357 Ma. The simplest interpretation is that the older age corresponds to the intrusion of the Lawrenceville pluton, causing the crystallization of andalusite, and the younger age represents a regional metamorphic event, causing retrogression. The presence of cohesive andalusite crystals and lack of orientation of the crystals with the foliation, indicate that the granite pluton was emplaced after the most intense deformation of the Hollister shearing event.
Date Awarded
2009
Department
Geology
Advisor 1
Brent E. Owens
Recommended Citation
Dorfler, Kristie M., "An Evaluation of the Areal Extent of the Andalusite-Bearing Rocks and the Timing of Low-Pressure Contact Metamorphism in the Hollister Shear Zone, Virginia" (2009). Geology Senior Theses. William & Mary. Paper 208.
https://scholarworks.wm.edu/geologyseniors/208
