STRUCTURAL ANALYSIS AND TIMING OF THE BROKEN BOW UPLIFT, OUACHITA OROGEN, OKLAHOMA

The Broken Bow uplift, a segment of the Ouachita orogen in eastern Oklahoma, exposes a nearly complete Cambrian to Late Pennsylvanian stratigraphic succession in the interior of a fold-and-thrust belt. The timing of uplift is constrained by Carboniferous syntectonic sediments and Late Carboniferous-Middle Permian fission track ages. The tectonic relationship between the Broken Bow uplift and the Benton uplift, located to the east in west-central Arkansas, is not well known from the published data. Previous workers suggest that a single anticlinal structure is present, while other researchers favor separate basement-cored crustal structures. Apatite and zircon fission track dates and retrodeformable cross sections place constraints on the timing of uplift and the relationships between these structures.

A preliminary zircon fission track date of 295.3±25.2 Ma from Silurian Blaylock Formation in the Broken Bow uplift indicates syn-tectonic cooling. Ongoing fission track work will refine the timing of formation for the Broken Bow uplift. Zircon fission track ages from the Benton Uplift range 307 ± 18.8 Ma to 333.4 ± 38.9 Ma and may indicate a westward younging of thrusting. This interpretation, supported by a pattern of vitrinite reflectance and illite crystallinity, is consistent with lower thermal maturation in the western part of the orogen. Analysis of retrodeformable cross sections indicates a viable interpretation of the crustal-scale structures and the location of major décollements. Restored cross sections in the Benton uplift to the east indicate 10-15% in the syn-tectonic sediments when compared to basement. New restored retrodeformable cross sections for the Broken Bow uplift may show a difference in the amount of shortening between the units which could suggest a similar deformation style, including a single anticlinal structure in both Oklahoma and Arkansas. Coupling retrodeformable cross sections with thermochronologic dates will provide the sequence of tectonic events and allow for a comparison to wedge models, which predict the timing of deformation from hinterland to foreland.