REGIONAL GRAVITY ANOMALIES OF THE OUACHITA OROGENIC BELT, SOUTHERN OKLAHOMA AULACOGEN, AND ADJACENT GULF COASTAL PLAIN: IMPLICATIONS FOR THE TECTONIC EVOLUTION OF THE SOUTH-CENTRAL U.S

A gravity data base of over 40,000 stations was used to generate regional Bouguer anomaly maps of the Ouachita orogenic belt, Southern Oklahoma aulacogen, adjacent cratonic areas, and the Gulf Coastal Plain. These maps were interpreted using 2-D forward modeling of four regional gravity profiles constrained by 96 wells and previous studies.

The gravity maps and models suggest that regionally high Bouguer gravity values, interspersed with lows associated with salt basins, are caused by a variably attenuated, but thinner continental crust beneath the Gulf Coastal Plain south of the Ouachita orogenic belt, as opposed to regionally lower Bouguer gravity values associated with thicker cratonic crust north of the Ouachita system. This crustal transition is also marked by a distinct gravity high that follows the buried interior zone of the Ouachita orogenic belt, but is a result of much more than just higher density metamorphic rocks of the interior zone. It is likely that this gravity high is caused by either 1) obducted oceanic lithosphere trapped within a “soft” suture zone created by late Paleozoic continent-continent collision at the southern margin of the Grenville craton, 2) an accreted volcanic arc, or 3) mid-crustal mafic rocks that intruded into highly extended continental crust during either the latest Precambrian breakup episode or during Mesozoic-Cenozoic extension that formed the Gulf Coastal Plain. Cratonward of this gravity high, large asymmetric negative Bouguer gravity anomalies mark the presence of deep foreland basins created during the Ouachita orogeny and filled with folded and thrusted passive margin accretionary wedge sedimentary rocks and volcaniclastic rocks deposited in the Ouachita trough.

The Southern Oklahoma aulacogen extends northwestward from the Ouachita orogenic belt just north of Dallas, Texas. This aulacogen is marked by a linear gravity high associated with the Wichita-Criner and Arbuckle uplifts that intersects the gravity high of the Ouachita system, and a gravity low associated with the southern Anadarko basin and Ardmore basin. The gravity highs of the aulacogen have been modeled as a combination of granitic basement and Precambrian mafic intrusions uplifted during the formation of the ancestral Rocky Mountains, while the lows are thick sedimentary basins.