NEW OBSERVATIONS ON THE EXTENT OF CAMBRIAN RIFTING IN COLORADO

The Southern Oklahoma aulacogen contains some of the largest structural features in North America and was tectonically inverted from a failed Cambrian-aged rift to a series of large uplifts and flanking basins during the Ancestral Rocky Mountain orogeny. This set of structures extends northwestward from the early Paleozoic Laurentian margin in northeasternmost Texas and can be interpreted to extend along this trend as far as the Uncompahgre uplift in western Colorado. Considerable geophysical data that reveal the deep manifestation of Ancestral Rocky Mountain structures in Oklahoma and Texas are available, and these data show that the scale and complexity of these structures is impressive. However, further to the northwest in New Mexico and Colorado, geological and geophysical data are scarce. Geological and geophysical data document that the amount of magmatic modification of the crust that accompanied the rifting is impressive in Oklahoma, but we can only infer the presence of rift structures from indirect geologic evidence. Gravity data show that extensive magmatic modification primarily in the form of mafic intrusions extends into the Texas Panhandle, but beyond that point, the anomalies are less pronounced, and there is some question about the nature and extent of the Cambrian rifting.

In addition to our recent studies in the Uncompahgre uplift region, 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, many of the topographically high outcrops of Proterozoic metamorphic rocks may actually be roof pendants, and the region may be an arm of the Southern Oklahoma aulacogen.