LITHOSPHERIC STRUCTURE OF THE SOUTHERN OKLAHOMA AULACOGEN AND SURROUNDING REGION AS DETERMINED FROM BROADBAND SEISMOLOGY AND GRAVITY

The Southern Oklahoma Aulacogen (SOA) is an easily recognized as perhaps the second largest gravity anomaly on a Bouguer gravity anomaly maps of North America. The SOA lies in the Granite Rhyolite province of Oklahoma and is characterized by large magnitude basement faults that were active during Cambrian rifting (550 Ma) and during the Ouachita orogeny in the late Paleozoic (313-285 Ma). The SOA was originally considered to be a failed rift of a triple junction associated with the Cambrian-aged opening of the Iapetan Ocean. This model is supported by the three-armed pattern of gravity highs at the junction of the SOA with the Ouachita orogen, the age of the bimodal series of gabbroic and rhyolitic rocks (that are clearly mantle derived), and the interpretation of a thick succession of clastic metasedimentary rock as rift-fill. More recently, some studies have suggested that the SOA is a leaky transform fault system that borders part of southern Laurentia. This study uses Earthscope broadband seismic to do single station analysis of Vp/Vs ratios and depths to various Crust and upper mantlee boundaries to resolve the nature of the SOA and to determine the depth (to the Moho) to which features related to the origins of the SOA are preserved.

Receiver functions analysis (RFs) from the Earthscope data found an abrupt change in depth to the Moho across the SOA in the western half of Oklahoma. Depths to the Moho on the south side of the SOA are generally shallower than to the north. RF analysis found several layers within the crust at 5 km, 13 km, and 27 km. All of these layers, including the Moho have a large change in depth at the high plains to rolling plains boundary. This trend is very most evident in the Moho where depths range from 41 km deep to 49 km. Additional processing is underway to map out variation in the Vp/Vs ratio throughout the region and into the mantle. RF analysis and Pn tomography and gravity will be used to produce a continuous model of the Moho beneath the region.