Mantle Reference Frame and Generation of Detached- and Flat-Slab Subduction Geometries In Caribbean Evolution

Opposing polarities of the Lesser Antilles/Aves Ridge and Middle American arcs prevented the Caribbean Plate from having significant E-W motion in the Indo-Atlantic mantle reference frame while both arcs were active (since Santonian, 85 Ma). During this time, the Americas drifted west relative to the mantle and their Proto-Caribbean margins collided with segments of the stationary Great Caribbean arc at southern Yucatan (70Ma), Bahamas (40Ma), and eastern Venezuela (12Ma). These margins had subductable oceanic slabs that faced partly westward in the direction of plate advance. Prior to collision at each, convergence occurred by American slabs entering sub-Caribbean mantle, like at today's Lesser Antilles. Upon collision, however, buoyant American continental crust choked subduction such that westward drift could only continue by detaching from and overthrusting the former oceanic slabs; the detached south Yucatan and Bahamian slabs should now underlie eastern Colombian Basin and Silver Plain, respectively. The Eastern Venezuelan slab may still be detaching by eastward tearing. In contrast, when W-drifting American continental crust forms hanging walls to E-dipping subduction (Andean type), flat-slab geometries result because the continental forearcs are thrust across original trench positions. Along Neogene SW Mexico, flat slab Cocos lithosphere enters the mantle due to its own velocity relative thereto, and creates an arc far from the trench. However, along NW Colombia, the Caribbean Plate, being fixed in the mantle, has NOT entered the mantle while being overridden by Colombia, possibly contributing to lack of an arc. At Andean settings like these, orogenic intensity depends on the rate of trenchward hanging wall advance relative to roll back, and the buoyancy (crustal age, thickness and petrology), of the downgoing plate. By comparing local Caribbean geo-histories at these two types of collisions, it appears that Andean-type examples can cause much greater uplift due to resultant doubling of the crust.