THE VALLEY AND RIDGE TO BLUE RIDGE PROVINCE TRANSITION NEAR LURAY, VIRGINIA: GEOLOGIC MAP & CATACLASTIC BRECCIAS
Current mapping covers the eastern portion of the Luray 7.5 minute quadrangle, focusing on the Chilhowee Group (Weverton, Harpers, Antietam Fms.) Their lithology varies somewhat throughout the mapping area, in particular the degree of deformation and weathering of the Antietam quartzite. Additionally, the Harpers Formation is transitional between its confining units and exhibits a range of grain sizes and mineralogy. The presence of ore-bearing brecciated siliciclastic outcrops is another feature of interest. The breccias vary in the degree of cataclastic fracturing and matrix content. They occur frequently in the Antietam formation and likely represent Alleghenian thrust fault activity. The fact that they are not laterally continuous, however, suggests that they may be, in part, vertical features created through dilation and/or collapse processes. Fracture dilation could have occurred as hydraulic injections into vertical jointing and other planes of weakness. Collapse of fractured bedding could also have formed some of these features through implosion of void spaces created during deformation. Better constraints on these lithologic and deformational features have improved delineation of formation contacts and fault locations in the region, with broader implications for the nature of Alleghanian orogenesis in western Virginia.