WHAT WAS BETWEEN THE YUCATAN PENINSULA AND THE OUACHITA MOUNTAINS AT THE END OF THE PALEOZOIC?: HISTORIES OF PRESENT STRUCTURES OFFER CLUES

A few years ago satellite gravity became available which imaged the oceanic spreading centers in the Gulf of Mexico, demonstrated how the Yucatan Peninsula rotated away from Laurentia and located the position of the Peninsula prior to rifting. The pre-rift location of the northern edge of the Peninsula was about 300 km from the early Paleozoic rift passive margin of southern Laurentia in Arkansas. What lay in that gap at the end of the Paleozoic?: 1) portions of the Peninsula, 2) island arc complexes, 3) micro-continental terranes, 4) thickened oceanic crust (ophiolites) or 5) some combination of the above.

The Sabine Uplift, Angelina-Caldwell Flexure, LaSalle Arch and the Monroe Uplift are structural features which lie in the area of the “gap” stretching from northeastern Texas across northern Louisiana to northwestern Mississippi. From the early Mesozoic to the present these features have complex histories of structural activity which are not easily explained with typical plate tectonic concepts. Recent understanding that dynamic topography, caused by the foundering of the Farallon Plate and of the Hess Conjugate (eastern portion of a Pacific spreading center volcanic accumulation which split into the Hess Rise on the Pacific Plate and its conjugate on the, now subducted, Farallon Plate), has strongly influenced elevations in the eastern United States, may offer explanations for the complex structural histories. It is likely that these explanations will contain clues to what lies in the “gap.”