MAGNETOTELLURIC MODELS IN THE OUACHITA OROGENIC BELT

The Ouachita Orogenic belt, a Late Paleozoic orogenic belt in the southern USA, stretches from Mississippi to northern Mexico. A key region is understanding the evolution of this belt is within the Ouachita Mountains in Arkansas and Oklahoma which contains the most extensive outcrops of the orogenic belt. Numerous geophysical investigations have, thus been conducted within this region with the most being PASSCAL wide-angle reflection/refraction experiment that extended from the Ouachita Mountains in Arkansas to the Sabine uplift in Louisiana. The resultant seismic model and subsequent gravity models along the seismic profile, extended into the northern Gulf of Mexico, imaged the Iapetan rifted margin and showed that it was not strongly deformed and contained a thick mass of Ouachita facies sedimentary rocks above transitional or oceanic crust outboard of the rifted margin of Laurentia. The longer gravity model showed that the southern US was the site of at least 3 extensional events in creating the Gulf of Mexico, where extension was finally successful south of the Sabine Uplift. Recent shear wave and surface wave tomographic models and receiver functions from the Earthscope experiment indicated that the Sabine Uplift is associated with faster and thicker crust and a region in the southern Ouachita Mountains in Arkansas is associated with lower velocities, thinned crust, and low Vp/Vs values indicative of crustal delamination. The more recent Earthscope magnetotelluric (MT) experiment collected long period data in and surrounding the Ouachita Orogenic belt and preliminary two- and three-dimensional models indicate that the southern Ouachita Mountains are associated with low electrical resistivities that extend to 60-70 km in depth, in the same region as the low seismic velocities and that the Sabine Uplift has higher electrical resistivity values again agreeing the seismic results.