GULF OF MEXICO BASIN STRUCTURE: WHERE IS THE BASIN’S NORTHEASTERN BOUNDARY AND WHAT ARE THE SABINE AND MONROE UPLIFTS?

Here we are about 50 years after Plate Tectonics was largely accepted as the explanation for most of the structural features of the Earth’s surface. Even though the Gulf of Mexico Basin (GoMB) has the greatest concentration of geologists and geophysicists in the world we still do not have an accepted Plate Tectonic explanation for the structures of the northern rim of the GoMB.

In particular, there are two vastly different locations proposed for a strike-slip system which bounds the GoMB on its northeastern side. One of these runs from Alabama to Oklahoma with a west-northwesterly strike. The other is almost co-located with the first in Alabama but runs to the area of the eastern end of the exposed Ouachita Mountains with a northwesterly strike. Authors have defended each of these in various ways. We need to settle on the location and nature of this boundary in order to develop a Plate Tectonic model for the GoMB. Maps of regional geologic and geophysical data yield a strong case for the northwesterly striking location for the boundary.

The Sabine Uplift in northeastern Texas and northwestern Louisiana and the Monroe Uplift near the join of Arkansas, Louisiana and Mississippi are uplifts at least 150 km (100 mi) in diameter. Each has been rising since the early stages of formation of the GoMB in the Mesozoic and likely is still rising today. What is the cause of these uplifts? Some authors have proposed that they are trapped island arcs related to the Appalachian – Ouachita forming late Paleozoic coalition of Pangaea. Others have proposed that they are “exotic terranes” trapped between the Laurentian and Gondwanan cratons during the Pangaean forming orogenic event. Another hypothesis is that they are “incipient metamorphic core complexes” resulting from thin slab rifting during the initial stages of the opening of the present GoMB. These are very different tectonic interpretations. We need to know the lithologies and structures of these uplifts.