LITHOSPHERIC CROSS SECTIONS ALONG THE SOUTHERN MARGIN OF NORTH AMERICA

The southern margin of Laurentia was produced by Neoproterozic to Cambrian age rifting. The resulting continental margin was relatively stable until the Ouachita-Appalachian orogeny, which involved a complicated succession of collisional events, followed by Mesozoic rifting. In order to investigate the lithospheric structure of the continental margin of southern and southeastern North America, we have complied geological and geophysical data along these margins. These data have been incorporated into six lithospheric models that are new or updated from previous models of lithospheric structure across the margin. One model extends from the craton in Tennessee; across the Black Warrior foreland basin, the Ouachita thrust belt, the Mississippi salt basin, and the Wiggins arch; and into the Gulf of Mexico. The most prominent features in this model are a crustal-scale block associated with the Wiggins arch and thinned crust under the Mississippi salt basin. A parallel north-south-trending model farther west shows another crustal-scale block, which extends across much of western Louisiana. In central Texas, no crustal block is found outboard of the Laurentian margin, and the transition from continental to oceanic crust is broad, possibly reflecting the effects of both Cambrian and Mesozoic rifting. In west Texas, however, a profile across the Devils River uplift indicates a large crustal block (Coahuila terrane) which occupies a large part of Coahuila in Mexico. A new model, extending from central Tennessee across the Appalachian thrust belt to central Florida includes a relatively dense body associated with the Suwannee terrane (African crust), which is sutured to the continental margin of Laurentia. Father west, all of the models except the central Texas model show a relatively narrow zone of transitional crust at the continental margin, suggesting transform faults along northwest-trending segments of the continental margin.