TECTONIC IMPLICATIONS OF CRUSTAL SCALE MODELS OF THE OUACHITA OROGENIC BELT

The southern margin of Laurentia was created by Neo-Proterozic to Cambrian age rifting. The resulting continental margin was relatively stable until the Ouachita-Appalachian orogeny which involved a complicated series of collisional events followed by Mesozoic rifting. However in the case of the Ouachita region, this margin is well preserved since the orogeny did not pervasively deform it. We have complied geological and geophysical data along the Ouachita portion of the margin and have created updated models of lithospheric structure across and along it. One model starts on the craton in Tennessee, crosses the Black Warrior foreland basin, the Ouachita thrust belt, the Mississippi salt basin, and the Wiggins arch before ending in the Gulf of Mexico. The most prominent features on this model are the crustal-scale block associated with the Wiggins arch and the crustal thinning under the Mississippi salt basin. Another N-S trending model located to the west shows another crustal scale block which extends across much of western Louisiana. On both of these models, the continental margin is narrow suggesting the presence of transform faulting. In central Texas, no crustal block is found outboard of the Laurentian margin and the transition from continental to oceanic crust is broad which may reflect the effects of both Cambrian and Mesozoic rifting. The cratonal region adjacent to the margin has been significantly deformed creating large structures such as the Southern Oklahoma aulacogen, the Reelfoot rift, and a series of foreland basins all of which represent significant modification of the crust. In spite of subsequent events, it seems clear that the formation of the Laurentian margin formed the structural framework of the region that has lasted to the present.