Caribbean structural breaks and plate movements

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Abstract
The Caribbean Plate was created as the North and South American Plates began to separate about 140 m.y. ago, allowing the Phoenix/Farallon spreading ridge to extend eastward. The Caribbean Plate was separated from the Phoenix/Farallon spreading ridge, about 110-100 m.y. ago, by a subduction zone near present-day Central America, connected by transform faults to the older Greater Antilles subduction zone. Geologic data from the margins of the Caribbean Plate indicate six important discontinuities in the history of the plate. Near the beginning of the Albian (110 m.y. B.P.), northeast-dipping subduction in the Greater Antilles zone may have been blocked by underthrusting of part of the Chortis Block of Central America, causing subduction to flip to southwest-dipping, perhaps followed by the beginning of subduction beneath Central America. A Santonian (85 m.y. B.P.) discontinuity may be the result of thickened oceanic crust formed at the Galapagos hot spot reaching the Central American subduction zone and blocking or modifying subduction. At the beginning of the Tertiary (66 m.y. B.P.), the Caribbean Plate changed its relative motion from northeastward to eastward and began to underthrust northern South America. In the Late Oligocene (27 m.y. B.P.), the Farallon/Phoenix Plate separated into the Nazca and Cocos Plates. The present-day emergence (5-0 m.y. B.P.) has not yet been correlated with plate motion changes. Major changes in plate arrangement and motion are thus reflected in the Caribbean Plate by major geologic discontinuities such as unconformities. Geologic structures along the plate margins are the resultants of the direction of relative plate motion, and of the type of lithosphere. Oblique plate motion produced horizontal slip accompanied by slow subduction without volcanism, by uplift and erosion, or by a combination of processes. Oceanic lithosphere forms relatively simple plate boundaries, as in the Greater Antilles, but continental lithosphere forms complex border zones composed of old structural blocks moving along ancient zones of weakness, as in northern South America.

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