U-PB DETRITAL ZIRCON SIGNATURE OF THE CARBONIFEROUS DEEP-WATER CLASTIC DEPOSITS IN THE OUACHITA MOUNTAINS AND ITS IMPLICATIONS

The southern margin of the North American continent transformed from a passive margin to an active margin during the Ouachita orogeny. Thick and near–continuous Paleozoic successions in the Ouachita Mountains provide a unique opportunity to document changes in both sedimentation and tectonics. In contrast to well-documented Taconic, Acadian, and Alleghenian orogenic events, limited detrital zircon studies of the Ouachita orogeny and associated successions have been published, and sediment sources of these deep-water, synorogenic clastics remain less constrained.

In this study, a total of six outcrop samples (n=617) from the Mississippian Stanley Group and Lower-Middle Pennsylvanian Jackfork and Johns Valley Groups were collected and processed for U-Pb detrital zircon geochronologic analyses to depict sediment sources and dispersal patterns during the Ouachita orogeny. Results show that the age distributions of the Carboniferous deep-water clastic deposits in the Ouachita Mountains are characterized by major peaks of the Paleozoic (~350-500 Ma), Grenville (~900-1350 Ma), and Midcontinental Granite-Rhyolite (~1350-1500 Ma), minor peaks of Yavapai-Mazatzal (~1600-1800 Ma) and Superior (> ~2500 Ma) provinces. These deep water clastics share great similarities with the Appalachian sources and are likely derived from similar sources. From the Mississippian Stanley Group to the Pennsylvanian Jackfork and Johns Valley Groups, the Yavapai-Mazatzal population shows marked enrichment (up to ~12%), suggesting Precambrian basement uplifts, possibly related to the Ancestral Rockies to the northwest, might be another potential source. Compilation and comparison show the Neoproterozoic age population (~550-800 Ma), most likely associated with the peri-Gondwana terrane to the south, ranges from 3% to 35% within the Mississippian Stanley Group. The variation indicates that the Stanley Group may have strong but short-lived local contribution from the Gondwana terrane in addition to the regional Appalachian sources. Overall, despite its proximal location, these Carboniferous deep-water clastic deposits in the Ouachita Mountains received limited contribution from the Ouachita orogenic belt itself.