9 Transcurrent Motion in the Southern Appalachians: Comparing Kinematics and Timing across the Orogen

Sunday, 1 April 2012
1:30 PM - 4:10 PM
Grand Ballroom, Salon C1

TRANSLATIONAL ODYSSEY OF CAROLINIA: PALEOZOIC BULK KINEMATIC REVERSAL IN THE SOUTHERN APPALACHIANS

Paper number: 9-2
Program: Symposia Sessions
Time: 1:50 PM – 2:10 PM

Authors

Abstract

Carolinia, the collection of Neoproterozoic-Ordovician peri-Gondwanan terranes that constitute the eastern flank of the southern Appalachians, records two main kinematic periods of Paleozoic deformation involving a transcurrent component. The earlier phase is best recorded along the Gold Hill shear zone, a prominent sinistral oblique thrust with 12 km of stratigraphic throw. The shear zone is kinematically linked to shortening structures in surrounding rocks and collectively they form a regional transpressional system. 40Ar/39Ar ages indicate that the main motion on this system is related to the Late Ordovician-Silurian Cherokee orogeny, marking the accretion of Carolinia to Laurentia. To the west of Carolinia in central Virginia, the Chopawamsic fault records sinistral shortening of Early Ordovician rocks that are stitched by the c. 437 Ma Ellisville pluton, indicating that the early kinematic phase extended into the Laurentian realm.

The later phase of transcurrent motion in Carolinia is best documented by displacement of the State Line flexure and by reactivation of the Gold Hill shear zone. The flexure is defined by the arcuate surface trace of structural trends in Carolinian rocks. It is interpreted to be the outboard portion of the Virginia promontory that has been dextrally displaced ~ 220 km. Regional constraints indicate that dextral motion took place between c. 430 Ma and 340 Ma. 40Ar/39Ar ages in the range of 390-360 Ma from the Gold Hill shear zone likely record fault reactivation during this kinematic phase. Dextral shear of this age has been documented in the Laurentian realm by other researchers. Elsewhere in Carolinia, this kinematic phase continued into the Permian. The Devonian stage of this phase may be related to dextral oblique accretion of Suwanee, whereas Carboniferous-Permian motion records the amalgamation of Pangea.

The bulk kinematic reversal from Late Ordovician-Silurian sinistral transpression to Devonian-Permian deformation with a dextral component in the southern orogen mirrors the bulk kinematic pattern in the northern Appalachians. This orogen-wide pattern likely reflects major plate rearrangement related to the Silurian closure of Iapetus.