Document Type
Thesis
Abstract
Brittle deformation is the hallmark of deformation in the upper crust and a fracture in a rock or outcrop can be an example of this. Structures of brittle deformation and their stress histories have been studied in the Petersburg granite by many geologists. Dalide and Diecchio (2005) claim that there is evidence of radial fractures from the Chesapeake Bay Impact Crater, while others believe that the Alleghanian Orogeny and Mesozoic rifting were the causes for deformation. The purpose of this study is to better define the deformation history of the Petersburg granite in the Richmond, Virginia area in the James River, and to also understand the stress history of the fractures in the outcrops. Four study sites were determined using Google Earth: a site near the 42™ Street Bridge, a site near the Manchester Bridge, a site near the Nickel Bridge, and Pony Pasture, all of which were well exposed outcrops in the river channel. The lineaments for each site were traced and rose diagrams were created. The four rose diagrams show a trend of a dominant set of fractures striking NNW/SSE and several smaller sets striking NE/SW. From these results we can conclude that sometime between 300 and 250 million years ago the Alleghanian Orogeny created the NE/SW fracture set with a NW/SE contraction, and sometime between 220 and 190 million years ago Atlantic rifting caused a N/S fracture set to deform with an E/W extension. There was no evidence of any radial fractures with an E/SE deformation pressure from the Chesapeake Bay impact crater, so this event does not seem to have had any effect on its formation.
Date Awarded
2012
Department
Geology
Advisor 1
Christopher M. Bailey
Recommended Citation
Ambrose, Megan, "The Kinematic History of Brittle Deformation in the Petersburg Granite, Richmond, Virginia area" (2012). Geology Senior Theses. William & Mary. Paper 264.
https://scholarworks.wm.edu/geologyseniors/264
