THE ROLE OF RIFTING IN THE TECTONIC EVOLUTION OF THE OKLAHOMA REGION

In the world of rift studies, the Southern Oklahoma aulacogen is a classic internationally known feature. This failed Cambrian-aged rift was inverted to form a series of very large uplifts and flanking basins during the Ancestral Rocky Mountain orogeny. This set of structures extends northwestward from the early Paleozoic rifted Laurentian margin in southeasternmost Oklahoma. Gravity data show that the inversion and extensive magmatic modification of the crust extends across the Texas Panhandle, but beyond that point, the anomalies are less pronounced. However, the magmatic modification of the crust during the Cambrian can be interpreted to extend along a northwest trend as far as the Uncompahgre uplift in western Colorado. In 2007 and 2008, the joint Oklahoma State University and University of Oklahoma field camp group conducted a gravity and magnetic survey of the region of the Gem Park and McClure Mountain mafic and ultramafic complexes in the Wet Mountains of southern Colorado. As would be expected, these Cambrian-aged intrusives produced strong gravity and magnetic signatures. However, the 40 mGal gravity high observed in 3 km across the Gem Park complex is remarkable. Based on this result, we extended our survey towards McClure Mountain and found that gravity and magnetic values continued to increase. These results, when merged with regional gravity and magnetic data, indicate that a large (> 100 km²) portion of the Wet Mountains is underlain by Cambrian mafic igneous rocks. Regional seismic data also indicate that this is the case. Thus, the region may be an arm of the Southern Oklahoma aulacogen. Also, new geophysical data indicate that the western arm of the massive Mid-Continent rift extends from Kansas across central Oklahoma. Its NNW-trending faults coincide at least to some extent with the ongoing earthquake swarm in central Oklahoma suggesting that old rift faults are experiencing reactivation.