Plate Tectonic Constraints on the Biogeography of Middle America and the Caribbean Region

Abstract

North America-Eurasia and South America-Africa were certainly joined in the classic reconstruction of Pangaea by Middle Triassic time. The line of collision and suture included the Appalachian Quachita-Marathon orogenic trend in the United States extending southwestward into what is now northeastern and southeastern Mexico and into Guatemala. Widespread continentality prevailed and there was no Gulf of Mexico or Caribbean Sea. In Late Triassic time and continuing into Early Jurassic time this construct began to founder by initial rifting between South America-Africa and North America. No oceanic crust was formed, however, thus Africa-South America were still completely connected by land or shallow sea to North America until mid-Jurassic time. During this same uppermost Triassic to Middle Jurassic period a largely continental magmatic arc was draped across the Pacific margin of southwestern North America and apparently continued unbroken into northwestern South America. Sometime in the Middle Jurassic oceanic crust began to form by seafloor spreading in the central Atlantic and Gulf of Mexico as separation of South America-Africa from North America accelerated. Once this dense crust began to form the trailing margins of the continents subsided below sea-level and construction of the Atlantic and Gulf coast continental shelves began. Evidence is quite conclusive that this ocean floor spreading did not reach the Pacific Ocean, but was transformed from the southwestern corner of the newly opened Gulf of Mexico northwestward across Mexico via a complex left-slip transform fault system that reached the Pacific margin near Los Angeles. In Early Cretaceous time spreading continued in the central Atlantic but extended southward into the southern Atlantic. As the main axis of spreading extended into the south Atlantic, spreading ceased in the Gulf of Mexico. The south Atlantic spreading initiated separation of South America from Africa, but they probably remained in partial contact via ridge-ridge transform faults until Late Cretaceous time. South America must have finally completely separated from North America in Early Cretaceous time, probably via a rift along the eastern edge of Yucatan and the Nicaraguan rise. By Late Jurassic time the Pacific continental margin arc had waned and was replaced by a complex, largely oceanic, magmatic arc whose position relative to southwestern North America and northwestern South America is not known. What we do know is that by Late Cretaceous-Early Tertiary time it had accreted against the Pacific margins of both. Connections between the continents are also not known but could have included a largely submarine magmatic arc, parts of which may have subsequently dispersed eastward as the Greater Antilles. Much of what is now Middle America is apparently underlain by oceanic crust at least as young as Late Cretaceous in age. By Late Cretaceous time the Greater Antilles magmatic arc seems to have fully formed and subsequently moved northeastward as a northeast-facing subduction system during Late CretaceousEarly Tertiary Laramide time. The Greater Antilles arc-trench system ceased activity in Late Eocene time as it collided with Florida and the Bahama platform and as Laramide orogeny waned throughout western North America. This was followed by a major plate reorganization in the Caribbean-Middle America region nearly 40 m.y. B.P. which established the Caribbean plate more or less as we know it today. The principal change was initiation of the Lesser Antilles magmatic arc as an east-facing subduction system that began to consume Atlantic ocean floor. Also, a west-facing subduction system may have formed about this time along a proto-Central American western margin of the Caribbean plate. However, much of what is now Central America may have initially been off southern Mexico. The northern and southern margins of the Caribbean plate evolved into complex transform and transpressive systems as North and South America moved westward past a nearly stationary Caribbean plate. These motions significantly fragmented the Greater Antilles into their present array. There is no evidence for any complete land connection between North and South America via the Greater and/or Lesser Antilles throughout later Mesozoic or Tertiary time. Nor is there any evidence for complete land connection via Central America and the Isthmus of Panama before Neogene time.