PRELIMINARY 3D MODELING OF THE OUACHITA FOLD-THRUST BELT AND ARKOMA FORELAND BASIN

Late Paleozoic convergence between Laurentia and Gondwana formed the Ouachita fold and thrust belt and Arkoma foreland basin in eastern Oklahoma and western Arkansas. Numerous previous workers have suggested that the Late Paleozoic contractional evolution was influenced spatially by pre-existing rift-related crustal structure. For example, 1) frontal thrust ramps nucleated along rift-related normal faults, 2) two major basement-cored anticlinal duplexes localized a set distance (~50 km N) from the edge of the rifted continental margin, and 3) the attitudes of folds and thrusts reflect, in part, local variations in pre-contractional basement structures. We elucidate these relationships by synthesizing existing studies into a 3D model. A compilation geologic map and ten regional structural cross sections (Arbenz, 2008) were digitized and imported into the Move (https://www.petex.com/products/move-suite) software. Three-dimensional surfaces representing a) the top of the Precambrian basement, b) the basal decollement of the thrust belt, c) several major thrusts, and d) pre-contraction normal faults were interpolated from the structural cross sections and surface exposures. The modeling elucidates along-strike variations in orogenic architecture. For example, we resolve a S-protruding promontory beneath the western part of the Ouachita Mountains. This promontory coincides with the more southern location of the Broken Bow uplift basement duplex (Oklahoma side) when compared with the more northern Benton uplift basement duplex (Arkansas side), where there is no promontory. Similar duplexes in other orogenic belts (e.g., Himalaya) have been inferred to mediate orogenic wedge taper and therefore control elevation and shortening magnitude (Long and Robinson, 2021). In the Ouachita Mountains, the locations of the basement duplexes was dictated by the initial margin width, a function of the pre-orogenic rifting.