Origin of Caribbean Plateau Basalts, the Arc-Arc Caribbean-South America Collision, and Upper Level Axis Parallel Extension in the Southern Caribbean Plate Boundary Zone

J. Pindell, Department of Earth Science, Rice University, 6100 Main Street, Houston, Texas, 77005 USA

Three new aspects of the Pacific-origin model for Caribbean evolution are proposed as part of the BOLIVAR program. First, mid-Cretaceous emplacement of the Caribbean Plateau Basalt Province is NOT due to the often-cited idea that the plate rode over Galapagos hot spot, whose proven age is less than Eocene and whose hypothetical Cretaceous mantle reference position was well west of Caribbean lithosphere, but rather due to progressive Cretaceous subduction of the Proto-Caribbean Spreading Center (a western arm of the Atlantic) beneath the Caribbean Plate as the Plate was engulfed between the American continents. A sub-Caribbean subduction shadow approaching the size of the Basalt Province is permissible on plate kinematic grounds, suggesting a Basin and Range [continental] analogue for Late Cretaceous extension, thinning and volcanism in/on Caribbean crust. Second, plate kinematic and tomographic data suggest that Cenozoic North Americaĺ─ýSouth America convergence was accommodated at a N-facing Proto-Caribbean subduction zone along northern South America prior to the E-wardly diachronous collision of the Caribbean Plate with South America. Further, incision depths to Albian and normal fault offsets reaching 500m on the regional Paleogene northern South American unconformity are too great to be explained by a migrating forebulge model (traditional arc-continent view of Caribbean-South America collision). Thus, Caribbean-South America interaction was an E-ward younging dextral oblique island arc-Andean arc collision, although the latter was amagmatic due to minimal rate and amount of Proto-Caribbean subduction, which took place above a vertically-interring Proto-Caribbean lithosphere. Deep, S-ward lessening Paleogene incision in northern South American basins is described as forearc uplift, ie thrusting of the South American hanging wall onto the flexurally arched and buttressed Proto-Caribbean lithosphere between the converging Caribbean and South American plates, prior to Caribbean collision. In addition, facies and sand/conglomerate mineralogy in the Scotland Fm of Barbados suggest that it represents part of the Proto-Caribbean, not Caribbean, Paleogene accretionary prism, and was accreted late (in the Mid-Miocene) into the Caribbean prism. Third, the highly-oblique Caribbean-South America collision above the Proto-Caribbean slab requires strong axis-parallel extension in the plate boundaryĺ─˘s basement rocks and sedimentary cover. Seismic examples and Middle Miocene sedimentary facies development in Trinidadĺ─˘s Central Range demonstrate how such extension occurs in upper structural levels of the orogen to complement axis-parallel extension at basement levels described elsewhere.