APPALACHIAN-OUACHITA BASINS AND TERRANES BENEATH THE GULF COASTAL PLAIN
In the Ouachita Mountains (AR), an accretionary prism overlies a basement-cored ramp anticline; on the north, large-scale down-to-south synorogenic basement normal faults step down into the Arkoma foreland basin. Geometrically similar faults ring the Ouachita foreland eastward beneath the Gulf Coastal Plain to the Black Warrior basin (MS), where deformation within a thick clastic succession suggests along-strike continuity of the accretionary prism. Farther south, a Mississippian–Pennsylvanian forearc basin overlies thin transitional or oceanic crust between the Alabama-Oklahoma transform margin of Laurentia and the accreted continental Sabine terrane (AR, LA). Igneous rocks on the Sabine terrane indicate a continental-margin arc associated with southward subduction of the Laurentian plate. Distribution of synorogenic sediment suggests collision of the continental-margin arc with the Texas and Alabama promontories, preserving the forearc basin within the Ouachita embayment.
The late Paleozoic Suwannee-Wiggins suture cuts across Laurentian basement on the southern corner of the Alabama promontory (AL, GA), marking continent-continent collision of Laurentia with the Gondwanan Suwannee terrane. The suture is a thick zone of tectonized crystalline lithons interlaced with mylonites, bounded on the south by gently folded Ordovician–Devonian strata and basement of the Suwannee terrane. The Wiggins block (AL, MS) may be part of the suture zone, which projects westward approximately on strike with the Sabine terrane. Emplacement of the Ouachita accretionary prism (~309 Ma) pre-dates continent-continent collision at the Suwannee-Wiggins suture (~300 Ma). Northwest-directed Appalachian thrusts imbricate the Ouachita foreland basin and truncate Ouachita thrust sheets (MS). More data are needed to resolve the along-strike change westward from a continent-continent collision (Suwannee-Wiggins suture) to the earlier arc-continent accretion (Ouachita orogen).