VARIATIONS IN LITHOSPHERIC STRUCTURE ALONG THE OUACHITA BELT AND THEIR RELATION TO TRANSFORM OFFSETS

As part of our ongoing effort to understand the structure and evolution of the Ouachita orogenic belt, we have complied and integrated a wide variety of data to produce a set of crustal scale transects that cross this orogenic belt. 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. Recent geophysical and geological studies in central Europe along the Trans-European suture zone (TESZ) region have delineated the rifted margin of Baltica, and it is quite similar to crustal models we have developed for the Ouachita margin. Our integrated seismic and gravity modeling efforts indicate that the Variscan orogeny in central Europe and 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.