Interpretation of Crustal Structure from Regional Gravity Anomalies, Ouachita Mountains Area and Adjacent Gulf Coastal Plain

Abstract

A gravity data base from more than 35,000 stations was used to generate a series of regional gravity maps of the Ouachita Mountains area including adjacent parts of the craton and the Gulf coastal plain. These maps were used in conjunction with information from 96 wells, data from pre-existing geophysical and geological investigations, and computer models to interpret four gravity profiles that transect the study area (approximately lat. 30-37°N, long. 91.5-99°W). These models, gravity maps, and previous investigations were then used to analyzed various regional gravity anomalies and to interpret the gross crustal structure of the region and its tectonic implications. These data suggest that variably attenuated continental crust lies beneath the Gulf coastal plain, south of the Ouachita system gravity gradient, as opposed to typical continental crust of the craton north of this gradient. This variation in crustal structure probably reflects the complexity of Eocambrian and early Mesozoic rifting in the area. The Arkoma basin gravity minima may result from the combined effect of a late Paleozoic foreland basin and an Eocambrian northwest-trending, rift-related basin. The Ouachita system interior zone gravity maximum varies along strike of this orogenic belt. This anomaly appears to be a good indicator of the position of the Eocambrian continental margin and associated rift zone. Gravity anomalies in the Gulf coastal plain appear to be a combined e fect of variable crustal attenuation, basins and uplifts, and mafic intrusions. Gravity maxima in the southern Oklahoma aulacogen result from uplifts and deep-seated mafic intrusions; gravity minima result from deep sedimentary basins.