ABSTRACT

Several diverse lines of evidence indicate that the pre-Gulf of Mexico position of South America was adjacent to the northern Gulf Coast of North America in earliest Mesozoic time, as originally suggested by Walper and Rowett. These include: 1) correlation of the boundary between Hercynian and pre-Hercynian terranes in Africa with the subsurface boundary between the southern Appalachians and the Florida platform in North America, 2) similarities in the inferred Triassic history of the Gulf and Atlantic coasts of North America; 3) recognition of significant left-lateral faulting in Mexico and Central America, which indicates more westerly positions of the various crustal blocks of Middle America prior to initiation of drift and, consequently, eliminates overlap of South America and Mexico of other reconstructions; 4) accommodation of the Florida-Bahama platform (assumed to be continental) by subsequent crustal extension and left-lateral faulting; 5) accommodation of Atlantic coast-Africa overlaps by crustal extension reflected in the on-and offshore Triassic basins, and 6) satisfaction of paleomagnetic data which seem to require more northerly positions of the Gondwana continents relative to the Laurasian continents in latest Paleozoic and earliest Mesozoic time.

The post-rifting history inferred from the reconstructions and other constraints suggests the Gulf began opening in a north-south direction in early Mesozoic time, while right-lateral, obliquely divergent movement was occurring along the Atlantic coast between Africa and North America. Such motion was accommodated in part by formation of the Triassic rift basins. Subsequently, in late Triassic time, Africa and South America began moving in a south-easterly direction relative to North America. During this period, and into the early Jurassic, the Florida-Bahama platform was extended and emplaced along left-lateral faults roughly parallel to the direction of plate motion. Eastward motion of Mexico and Central America along left-lateral faults continued with opening of the Gulf of Campeche in Jurassic time, and movement of the various crustal fragments of Middle America into the Caribbean region during the Cretaceous and early Cenozoic. Contemporary east-west left-lateral movement is occurring along the plate boundary separating the North American and Caribbean plates.

These inferences suggest that the Gulf of Mexico is older than the Atlantic, and is underlain by the oldest oceanic crust still preserved in the world ocean basins. Further, it is likely that initial fragmentation of Gondwana from Laurasia involved a large component of strike-slip motion, concentrated along the axes of the older Appalachian-Hercynian mountain belts.