MAPPING STRUCTURAL BLOCKS IN THE DRAPER MOUNTAIN AREA, VIRGINIA, USA

The Draper Mountain block is a series of folded and faulted sedimentary rocks in the Valley and Ridge Province of southwestern Virginia, USA. Recent 1:24,000-scale geologic mapping in the area funded by the USGS STATEMAP program utilized newly available 1-meter lidar to refine and build upon the complex geologic framework that was largely established in the early- to mid-20^th century. The geologic map and cross sections produced during this project represent one of many possible interpretations, and the exact placement of faults is still unclear in several areas due to complex deformation and stratigraphy.

The Draper Mountain anticline is asymmetric, with a steep to overturned forelimb, and an overturned synclinal backlimb. It is structurally above the Cove Mountain thrust sheet and structurally below the Pulaski and Max Meadows thrust sheets, which are far-traveled and structurally below the Blue Ridge thrust system. The Draper block and adjacent thrust sheets each have distinct stratigraphy, and different lithologic units accommodate strain differently. Thick-bedded packages of well-cemented rocks (typically sandstone and dolostone) generally form long-wavelength folds separated by widely spaced thrust faults. Thin-bedded and poorly cemented rocks (typically shaly limestone and mudstone) often have a well-developed “proto-metamorphic” cleavage which is easily visible on highly weathered surfaces, short-wavelength parasitic folding, and closely spaced faults with relatively minor offset. Stratigraphically heterogenous packages of thin- to medium-bedded clastic and carbonate rocks of the Rome Formation are particularly good at accommodating strain and are seen folding around the east end of Draper Mountain. Slickenlines and en echelon tension gashes within the Rome Formation indicate significant oblique motion on some faults south of Draper Mountain.

Geologic cross sections as early as 1925 have interpreted the Pulaski and Max Meadows thrust sheets as being tightly folded on the southern flank of the Draper block. Further work is required to determine whether the Draper block is a folded continuation of the underlying Cove Mountain block, a rootless folded structure in the hanging wall of a thrust fault, or a far-traveled orphaned block.