Fold-to-Fault Progression of aMajor Thrust Zone Revealed in Horses of the NorthMountain Fault Zone, Virginia andWest Virginia, USA

摘要

Themethod of emplacement and sequential deformation of major thrust zones may be deciphered by detailed geologicmapping of these important structures. Thrust fault zonesmay have added complexity when horse blocks are contained within them.However, these horses can be an important indicator of the fault development holding information on fault-propagation folding or fold-tofault progression. The North Mountain fault zone of the Central Appalachians, USA, was studied in order to better understand the relationships of horse blocks to hanging wall and footwall structures. The NorthMountain fault zone in northwestern Virginia and eastern panhandle of West Virginia is the Late Mississippian to Permian Alleghanian structure that developed after regionalscale folding. Evidence for this deformation sequence is a consistent progression of right-side up to overturned strata in horses within the fault zone. Rocks on the southeast side (hinterland) of the zone are almost exclusively right-side up, whereas rocks on the northwest side (foreland) of the zone are almost exclusively overturned. This suggests that the fault zone developed along the overturned southeast limb of a syncline to the northwest and the adjacent upright limb of a faulted anticline to the southeast.