THE CONSEQUENCES OF NON-PLANE STRAIN, GENERAL SHEAR, AND TRICLINIC DEFORMATION IN THE APPALACHIAN OROGEN

Deformation fabrics preserved in rocks of the Blue Ridge and Piedmont provide evidence for understanding the kinematics of material movement in the Appalachian orogen. Strain patterns in the Appalachians are commonly the product of one or more heterogeneous deformations and the relationship between three-dimensional strain and material flow is complex. In many instances rock fabrics record the cumulative effect of deformation and provide a record of the overall kinematics not just a partial glimpse of the deformation history. Ordovician plutonic rocks from the Virginia Piedmont experienced multiple deformation episodes; yet preserve one penetrative foliation and lineation that records the cumulative deformation. Cumulative deformation resulted in zones of strongly non-plane strain, modest amounts of orogen-normal shortening, and significant (~10 to 70%) orogen-parallel material elongation. In the Virginia Blue Ridge, mylonite zones followed general shear deformation paths with both monoclinic and triclinic symmetries. These zones record both northwest-directed reverse movement as well as a component of orogen-parallel strike-slip movement. The widespread flattening strains preserved in Blue Ridge mylonites require significant orogen-parallel material movement. Quantitative strain and vorticity data from both low-strain and high-strain domains are useful because they allow for palinspastic retrodeformation and restoration of crustal blocks to their pre-deformation geometries and geographic locations.