SOME NEW OBSERVATIONS ON THE EXTENT OF THE SOUTHERN OKLAHOMA AULACOGEN AND ITS HISTORY OF VERTICAL MOVEMENTS

The Southern Oklahoma aulacogen is a classic example of a failed intracratonic rift that formed in the Cambrian and was tectonically inverted to form a series of large uplifts and flanking basins during the Ancestral Rocky Mountain (ARM) orogeny. This set of structures extends northwestward from the early Paleozoic Laurentian margin in northeasternmost Texas and has been interpreted to extend along this trend as far as the Uncompahgre uplift in western Colorado. The late Paleozoic intraplate deformation that inverted the SOA rift structures and formed the remainder of the ARM is both massive and enigmatic. The Wichita uplift is the largest ARM structure experienced ~10 km of uplift that exposed a variety of Cambrian igneous rocks before being worn down to a near seal-level peneplain. Burial and preservation of the topography requires active subsidence of at least 1 km in the early-middle Permian. The Uncompahgre uplift (Colorado) exhibits at least 6 km of structural relief that formed during ARM orogenesis. The Pennsylvanian-Permian Cutler Formation wedges toward the uplift. New field data indicate the youngest Cutler strata onlap the basement and bury ~1 km of relief carved in the uplift that preserved in the form of modern Unaweep Canyon. Recent drilling results show that this canyon contains a basal unit of late Paleozoic age. Preservation of significant paleorelief beneath Permian strata on both of these widely separated uplifts along with regional evidence for the disappearance of coarse clastic mantles around ARM uplifts suggests the uplifts and their immediate surroundings succumbed to active (tectonic) subsidence soon after reaching their apogee. Geophysical data show that both of these features involve large-scale reverse faulting that brought large mafic massifs from mid-crustal depths near or to the surface. The load represented by these massifs may have played a role in the subsidence. In addition, 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. These Cambrian-aged intrusives produced strong gravity and magnetic signatures indicating they are large and possibly represent an arm of the Southern Oklahoma aulacogen.