A BALANCE OF PAYMENTS IN SOUTHERN LAURENTIAN TERRANES: PRECORDILLERA, LLANORIA, AND SUWANNEE

A Laurentian "export," the Precordillera terrane of northwestern Argentina, was rifted from the Ouachita embayment of southern Laurentia in Early Cambrian time and accreted to western Gondwana in Ordovician time.

A passive margin persisted around the Ouachita embayment until middle Mississippian time (in contrast to the Ordovician-Mississippian polyphase orogenic history of the Blue Ridge margin of Laurentia). Diachronous destruction of the Ouachita passive margin progressed westward from the Black Warrior foreland basin in Mississippian time to the Arkoma foreland basin in Pennsylvanian time. Early concepts of an "Ouachita geosyncline" included "Llanoria" as a continental borderland. "Llanoria" now encompasses obduction of an accretionary prism (Ouachita thrust belt) over the passive-margin shelf edge, as well as accretion of a forearc basin and arc terrane (now beneath the Gulf Coastal Plain) to Laurentia. Remaining questions include whether the arc was continental-margin or oceanic, and whether Llanoria included continental crust.

The Suwannee terrane and Suwannee-Wiggins suture record continent-continent collision of Africa with southeastern Laurentia. In concert with continent-continent collision, crystalline thrust sheets drove foreland thrusting; and accreted terranes tectonically replaced imbricated passive-margin carbonate rocks on Laurentian crust (in contrast to obduction and lack of crystalline thrust sheets in the foreland of Llanoria). Initial dispersal of synorogenic sediment and down-to-southeast flexural subsidence along the Alabama Appalachian thrust belt suggest Early Pennsylvanian collision along the Suwannee-Wiggins suture, clearly post-dating initial collision of the Llanoria arc along the Laurentian margin at the Black Warrior basin.