Chapter 2 New constraints on the late cretaceous/tertiary plate tectonic evolution of the caribbean

Abstract

We review the plate tectonic evolution of the Caribbean area based on a revised model for the opening of the central North Atlantic and the South Atlantic, as well as based on an updated model of the motion of the Americas relative to the Atlantic-Indian hotspot reference frame. We focus on post-83 Ma reconstructions, for which we have combined a set of new magnetic anomaly data in the central North Atlantic between the Kane and Atlantis fracture zones with existing magnetic anomaly data in the central North and South Atlantic oceans and fracture zone identifications from a dense gravity grid from satellite altimetry to compute North America-South America plate motions and their uncertainties. Our results suggest that slow sinistral transtension/strike-slip between the two Americas at rates roughly between 3 and 5 mm/year lasted until chron 25 (55.9 Ma). Subsequently, our model results in northeast-southwest-oriented convergence until chron 18 (38.4 Ma) at rates ranging between 3.7 ± 1.3 and 6.5 ±1.5 mm/year from 65°W to 85°W, respectively. This first convergent phase correlates with a Paleocene-Lower Eocene calc-alkaline magmatic stage in the West Indies, which is thought to be related to northward subduction of Caribbean crust during this time. Relatively slow convergence until chron 8 at rates from 1.2 ± 0.9 to 3.6 ± 2.1 mm/year from 65°W to 85°W, respectively, is followed by a drastic increase in convergence velocity. After chron 8 (25.8 Ma), probably at the Oligocene-Miocene boundary, this accelerated convergence resulted in 92 ± 22 km convergence from chron 8 to 6, 127 ± 25 km from chron 6 to 5, and 72 ± 17 km from chron 5 to the present measured at 85°W near the North Panama Deformed Belt at convergence rates averaging 9.6 ± 3.1 and 9.6 ± 2.1 mm/year from chron 8 to 6 and chron 6 to 5, respectively, slowing down to 5.2 ± 1.3 mm/year after chron 5. Neogene convergence measured at the eastern Muertos Trough, at 17.5°N, 65°W, is 41 ± 18 km from chron 8 to 6, 58 ± 25 km from chron 6 to 5, and 22 ± 17 km from chron 5 to present day, at rates between 4.4 ±1.7 and 1.6 ± 1.0 mm/year. These well-resolved differential plate motions clearly show an east-west gradient in plate convergence in the Neogene, correlating well with geological observations. We suggest that the Early Miocene onset of underthrusting of the Caribbean oceanic crust below the South American borderland in the Colombian and Venezuelan basins, the onset of subduction in the Muertos Trough, and folding and thrust faulting at the Beata Ridge and the Bahamas, and the breakup of the main part of the Caribbean plate into the Venezuelan and Colombian plates, separated by the Beata Ridge acting as a compressional plate boundary (Mauffret and Leroy, Chapter 21) may all be related to the accelerated convergence between the two Americas. The main differences with previous analyses are that (1) our model results in substantial variations in convergence rates between the two Americas after chron 25 (55.9 Ma), (2) we have computed uncertainties for our North America-South America plate flow lines, and (3) we show Tertiary Caribbean plate reconstructions in an Atlantic-Indian hotspot reference system. Our absolute plate motion model suggests that the Caribbean plate has been nearly stationary since chron 18 (38.4 Ma). The east-west gradient in convergence between the Americas in the Neogene has not resulted in substantial eastward motion of the Caribbean plate, but rather contributed to causing its breakup into the Colombian and Venezuelan plates along the Beata Ridge where east-west-oriented compressional stresses are taken up. Our model also suggests that the eastward escape of the Caribbean plate in a mantle reference frame ceased when seafloor spreading started in the Cayman Trough, if the current interpretation of magnetic anomalies in the Cayman Trough is not grossly in error. Our model suggests that the opening of the Cayman Trough was accomplished by westward motion of the North American plate relative to a stationary Caribbean plate in a mantle reference system. This implies that subsequent North America-Caribbean and South America-Caribbean tectonic processes were no longer dominated by Cocos-Caribbean and Nazca-Caribbean plate interactions, as the latter had ceased to drive the Caribbean plate eastwards. We conclude that the west-northwestward motion of South America relative to a trapped, stationary Caribbean plate caused oblique collision along the passive margin of eastern Venezuela in the Neogene.