MAGNETOTELLURIC ANALYSIS OF THE SOUTHERN OKLAHOMA AULACOGEN

The Southern Oklahoma aulacogen is a major tectonic feature in the south-central United States that is characterized by large amounts mafic intrusive material formed in the Early Cambrian and an array of northwest-trending faults. Neoproterozoic-Cambrian rifting of Rodinia reflected in northwest-trending faults within the SOA and the intrusion of an extensive igneous suite. Later, the Paleozoic Ouachita orogenesis, previously formed faults of the SOA were reactivated as reverse and strike-slip faults giving rise to the Arbuckle, Wichita and Amarillo Uplifts. Deep seismic reflection/refraction surveys, gravity modeling and broadband seismic studies have shown that the base of the Paleozoic sedimentary layer ranges between 4 to 11 km, the Cambrian intrusions are at least 14 km thick and the Moho depths range from 36 to 48 km with the shallower regions being related to low velocity zones directly under the SOA. However, the formation of the SOA has been controversial with both rifting-related or transform fault models being both applied to explain its origin. In this study, Earthscope and broadband magnetotelluric data were analyzed. A dimensionality analysis indicated that the electrical resistivity structure is three-dimensional. Thus, the data were inverted for a three-dimensional electrical resistivity structure. The resultant models indicated that the SOA is associated with a lower electrical resistivity down to 80-100 km and the lower lithosphere is associated with a lower electrical resistivity to the NW of the SOA down to 280 km. The lower electrical resistivity crustal region may represent shear zones and suggests that the SOA may have been formed by strike-slip processes.