THRUST FAULTING AND CRUSTAL SHORTENING IN THE BLUE RIDGE FOOTWALL: AN EXAMPLE FROM THE WHITE HOUSE FARM, PAGE VALLEY, VA

Recent, detailed bedrock mapping in the Hamburg quadrangle west of Luray, Virginia, provides evidence for significant crustal shortening in the footwall of the Blue Ridge thrust system. The White House Farm, located along Virginia Route 211 and the South Fork of the Shenandoah River encompasses 270 acres in the southeastern portion of the quadrangle. The White House, listed on the Virginia Landmarks Register, was built in 1760 and was the first European settlement in the Shenandoah Valley as part of an original 5,000 acre land grant. The most visible establishment is a brick farmhouse built in 1890 that is now being restored to that era.

Digital field mapping at the farm focused on the lithologic sequence and fold patterns to determine whether 1. Along-strike, west-vergent folds in a nearby quarry could be documented in the farm, and 2. Whether the localized folding is derived from thrust faulting. Lithologies in evidence at the farm are Ordovician carbonates, specifically the Beekmantown dolomite along the eastern margin of the farm and the Edinburg micritic limestone in the west. Stratigraphically, the New Market and the Lincolnshire formations should crop out between these two formations. However, our mapping shows no evidence for the New Market or Lincolnshire formations anywhere on the farm. The missing formations, nearby along-strike folding in the Edinburg formation, small scale reverse faults, and the proximity of the Blue Ridge thrust system to the field area suggests significant crustal shortening due to thrust faulting.

Where the Lincolnshire and New Market formations crop out in Page County they total approximately 100 - 250 feet in thickness. This suggests that the hypothesized thrust fault produced at least 100 feet of shortening in addition to shortening from folding in the footwall carbonates. Quantifying the amount of crustal shortening associated with this fault allows us to further determine the minimum amount of shortening related to the Blue Ridge thrust system during the Alleghanian orogeny. Future work in the local area around the White House Farm is needed to look for evidence, such as fault breccia and slickensides, to further evaluate the hypothesized thrust fault.