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The AAPG/Datapages Combined Publications Database
GCAGS Transactions
Abstract
Congenetic Relations of Atlantic Ocean and American Mediterranean
DeWitt C. Van Siclen (1)
ABSTRACT
Key to understanding the formative relationships between the early Atlantic Ocean, Gulf of Mexico and Caribbean Sea is the most southwesterly strip of North Atlantic lithosphere, which was produced by a mantle plume that can be traced to the present Sierra Leone Rise off Africa. During the Triassic, this plume was located beneath the three radial rifts within the supercontinent of Pangea that ultimately separated the Central Atlantic continents. After driving northern Florida to the north and west, this plume continued to occupy the resulting reentrant between future Africa and South America until they separated early in the Cretaceous. From this reentrant, it fed a unidirectional spreading ridge several hundred miles (about 300 km) long that stayed over the plume. There it generated a continuous strip of unusually buoyant oceanic lithosphere, while the usual symmetrical seafloor spreading was in progress on both sides. Presuming that the buoyancy was imparted by siliceous constituents from the flanking continents, the product will be referred to as the siliceous lithospheric strip. It begins beneath southern Florida and continues under the Bahama Platform.
Unidirectional spreading ended, however, when the Central North Atlantic spreading ridge, migrating westward after its final jump back to the edge of Africa, broke through the siliceous lithospheric strip off the northeast corner of South America. This projected symmetrical Central North Atlantic spreading across the southeastern Caribbean, thus opening a gap in the siliceous lithospheric strip that extends from the tip of the Bahama Platform almost to Barbados Island. There the strip resumes under a cover of younger materials and continues off northeastern South America to the Demerara Plateau which, with the similar Guinea Plateau off Africa, formed over the plume after undirectional spreading had ended. Opposite the center of the gap in the siliceous lithospheric strip, the bathymetry and sediment isopachs east of the Puerto Rico Trench reveal a low, northeast-trending basement ridge that still marks this extinct Central North Atlantic-Caribbean spreading center.
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