U-PB DETRITAL ZIRCON SIGNATURE OF THE OUACHITA OROGENIC BELT

The Late Paleozoic Ouachita fold-and-thrust belt extends from the southern terminus of the Appalachian thrust belt in eastern Mississippi up through central Arkansas, southeastern Oklahoma, and Texas terminating in northeastern Mexico. A series of Carboniferous foreland basins were formed sequentially to the thrust front. Although it is understood that the interaction between the Laurentian craton and the Appalachian-Ouachita orogenic belts controlled sediment routing in the southern midcontinent region throughout the Paleozoic, previous studies have been unable to discern sediments derived from the Ouachita orogenic belt.

In this study, six Ordovician to Mississippian aged clastic units from the Ouachita Mountains in central Arkansas were sampled and tested using U-Pb detrital zircon geochronology. Three major age peaks are prominent, including the Grenville Province (~0.9-1.2 Ga), the Granite-Rhyolite Province (~1.3-1.5 Ga), and the Superior Province (>~2.5 Ga) in Ordovician to Silurian aged Crystal Mountain Sandstone, Blakely Formation, and the Womble Shale. A change in this signature becomes clear at the beginning of the Carboniferous from Early Mississippian Stanley Group samples showing the additional Paleozoic age peak (~490-520 Ma) potentially derived from the Appalachian orogenic belt to the east. This stratigraphic variation of detrital zircon age signature suggests that the transition from a passive to an active margin in the Ouachita trough started, at the latest, in early Mississippian times. Results of this study also provide an important reference for provenance interpretation in southern Midcontinent.