OROGEN-SCALE SIGNIFICANCE OF DEXTRAL STRIKE-SLIP FAULTS: LINKS BETWEEN TERRANE COLLISION, DEFORMATION AND CLASTIC WEDGE SEDIMENTATION

Tectonic models for the Appalachian orogen must reconcile faults with large lateral displacements (>100 km). Dextral strike-slip motion has occurred along many faults in the southern Appalachians, including the Chattahoochee and Burnsville faults in the Blue Ridge, and two episodes of dextral deformation associated with the Brevard fault zone in the Inner Piedmont. These faults played important roles in the redistribution of southern Appalachian terranes and must be accounted for in tectonic models of the orogen. Located in the Inner Piedmont, the Cat Square terrane (CSt) contains Silurian-Devonian, sillimanite-grade pelite, psammite, and minor mafic and ultramafic rocks, intruded by Late Silurian and Devonian to Mississippian peraluminous granitoids. The western boundary of the CSt is the Brindle Creek fault and is separated from the Carolina superterrane to the east by the central Piedmont suture. The CSt contains Laurentian, peri-Gondwanan, and Silurian (~435 Ma) detrital zircons, an assemblage similar to Silurian-Devonian rocks in the crystalline core of New England. Possible sources of Silurian detrital zircons include plutons in the terranes of the Virginia Piedmont or a more northerly source. Estimates of net SW-directed displacement of the ~15 km wide Brevard fault zone from bulk strain of deformed igneous bodies and map-scale sheath folds yield displacements of 250-450 km. This restores the Inner Piedmont to a position near the Pennsylvania embayment and creates orogen-scale links between Devonian-Mississippian metamorphism and deformation in the crystalline core and clastic wedge sedimentation in the foreland, source of Silurian zircons, and possible correlation with New England terranes. We suggest that the Carolina superterrane collided obliquely with the Laurentian margin, beginning near the NY promontory. The CSt was deposited in the intervening remnant ocean basin located in the Pennsylvania embayment, possibly as a southerly offshore extension of the Putnam-Nashoba terrane. As collision progressed, the remnant ocean basin zippered closed from NE to SW and the diachronous foreland clastic wedges migrated to the SW. Oblique collision of Africa during the Alleghanian orogeny transported the Inner Piedmont to its current position in the orogen.