MAGNETOTELLURIC MODELS ACROSS THE OUACHITA OROGENIC BELT IN ARKANSAS AND OKLAHOMA

The Ouachita Orogenic belt is the longest orogenic belt in the US. A key region is understanding the evolution of this belt is the Ouachita Mountains in Arkansas and Oklahoma. Additionally, the most important study in understanding the lithospheric structure of the southern US is the PASSCAL wide-angle reflection/refraction experiment that extended from the Ouachita Mountains in Arkansas to the Sabine uplift in Louisiana and the subsequent gravity model in this region. The seismic experiment 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 gravity model extended the seismic experiment into the Gulf of Mexico and 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. The recent Earthscope magnetotelluric (MT) experiment collected long period data in the Ouachita Orogenic belt. Preliminary two-dimensional models of the widely spaced (70 km) data indicates that the main Ouachita sedimentary units are electrically conductive, the Sabine Uplift is relatively resistive and an electrically low conductive region is found in the same region as the dense and seismic high velocity region that may be associated with the transitional or ocean crust.