VARIATIONS IN LITHOSPHERIC STRUCTURE ALONG THE OUACHITA OROGENIC BELT

To understand the lithospheric structure of the Ouachita orogenic belt and how it varies across the entire belt, we have complied and integrated different data sets to produce a set of lithospheric scale transects that cross this orogenic belt. These transects range from the southern Appalachians to the Marathon Mountains in west Texas. The final transects are presented as gravity models but they are constrained by the available seismic reflection/refraction, magnetic, well and geological data. The key transect is based on the PASSCAL wide-angle reflection/refraction experiment that extended from the Ouachita Mountains in Arkansas to the Sabine uplift in Louisiana. This experiment imaged the Iapetan rifted margin and showed that it was not strongly deformed. It also revealed a thick mass of Ouachita facies sedimentary rocks above transitional or oceanic crust outboard of the rifted margin of Laurentia. Our integrated models and geologic constraints show that the Appalachian and Ouachita orogenic belts were formed during assembly of Pangea (by ~270 Ma), and were driven onto the Iapetan rifted margin by collisions with arcs, exotic terranes, and other continents. They also show that the sinuous curves of the Appalachian-Ouachita orogen mimic the shape of the Iapetan rifted margin and subsequent passive-margin shelf edge. Our results show that all around the Ouachita thrust belt, imbricated continental slope facies (in an accretionary prism at the leading edge of an arc complex) were thrust onto the continental shelf. Our integrated seismic and gravity modeling constrained by well and geological data efforts indicate that the Ouachita orogeny appear to be the results of soft collisions that have left the pre-orogenic rifted margins largely intact and reflect the complex interactions of compressional and strike-slip deformation.