THOUGHTS ON THE RELATIONSHIP OF STRUCTURES OF THE NORTHERN MARGIN OF THE GULF OF MEXICO BASIN TO EARLY RIFTING OF THE BASIN

Lineaments and structures indicate that the basement of the North American Continent east of the Rocky Mountains is fundamentally fractured in orthogonal directions, NW and NE. This set of weaknesses has controlled structures developed during break-ups and collisions since at least the Neoproterozoic Iapetian rifting of Laurentia. Major portions of the northeastern and northwestern margins of the Gulf of Mexico basin (GOMB) are bounded by rifts and transforms from this rifting event. Subsequent Paleozoic Appalachian-Ouachita collision occurred against this Precambrian margin resulting in collapse or overriding of promontories and filling of embayments, including the Ouachita embayment within which the GOMB formed. The NW – NE pervasive fractures also exist within the Ouachita embayment filling basement and controlled Mesozoic rifting of the GOMB. Some structures of the northern margin of the GOMB; e.g., LaSalle Arch, Angelina-Caldwell Flexure and southern portion of the North Louisiana Salt Basin; appear, by their orientations, to have been influenced by these fractures. Others; e.g. Sabine Uplift, Monroe Uplift and the Arkansas-Louisiana portion of the North Louisiana Salt Basin; appear not to be so directly related to these fractures.

Interpretations of maps of gravity, crustal thickness and heat flow and cross-sections of the northern GOMB lead to the hypothesis that the initial opening of the GOMB was by broad extension (from the NW to the SE) similar to the broad extension which in western North America resulted in Metamorphic Core Complexes. However, subsequent deposition has prevented exposure of the GOMB complexes resulting in “Incipient Metamorphic Core Complexes (IMCC),” e.g. Sabine and Monroe Uplifts. These IMCCs have a long history of rising and probably are continuing to rise today.