GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 294-2
Presentation Time: 2:00 PM


THOMAS, William A., Emeritus University of Kentucky, Geological Survey of Alabama, P.O. Box 869999, Tuscaloosa, AL 35486-6999, LAWTON, Timothy F., Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78758, GEHRELS, George E., Department of Geosciences, University of Arizona, Tucson, AZ 85721 and MUELLER, Paul A., Department of Geological Sciences, University of Florida, Williamson Hall, Gainesville, FL 32611

Gondwanan terranes along the southern Alleghanian–Ouachita–Marathon orogen vary in composition and accretion history. Detrital-zircon (DZ) data from the orogenic foreland demark sediment dispersal from the terranes.

In the subsurface southernmost Appalachians, the Suwannee terrane has Neoproterozoic volcanic basement and Cambrian–Devonian sedimentary cover with DZ populations of almost exclusively Eburnian (2200–1950 Ma) and Pan-African (700–500 Ma) ages. A dextral suture has zircon-overgrowth ages of ~300 Ma, marking the time of transpressional accretion.

On the west, south of the Marathon salient, the Coahuila terrane includes Mesoproterozoic and Neoproterozoic basement, as well as the late Paleozoic Las Delicias arc (331–270 Ma). Mississippian forearc deposits include tuff layers correlative with the ages of earliest Las Delicias magmas. DZ populations attributable to Coahuila include distinctive Gondwanan ages, especially 800–500 Ma. An angular unconformity brackets a middle Wolfcampian (~295 Ma) age of latest Marathon thrusting.

Between Suwannee and Coahuila, continental crust of the Sabine terrane south of the Ouachita salient underlies the Gulf Coastal Plain. Drilling has not penetrated basement rocks, but siliciclastic and volcanic rocks have been drilled along the northern edge of the Sabine terrane. A forearc succession includes ~328–320-Ma tuffs from a magmatic arc along the leading edge of Sabine; xenocrystic grains have ages similar to those in Coahuila. An angular unconformity between Atokan and Demoinesian strata in trailing Ouachita thrust sheets indicates latest thrusting at ~310 Ma, similar to a ~309 Ma age of youngest deformed beds in the frontal thrust belt. East of the Ouachita salient, the Appalachian thrust front truncates the older Ouachita thrust sheets.

Close matches of DZ populations in the Marathon and Ouachita (Fort Worth basin) forelands indicate a provenance in Coahuila and probably Sabine, respectively, but southern Appalachian synorogenic detritus does not contain significant Suwannee-derived sediment. DZ ages in Permian redbeds suggest sediment dispersal from Coahuila and Sabine across the orogen and onto southern Laurentia, reaching at least as far as the Anadarko basin, perhaps driven by increased regional aridity and attendant sediment yield.