THE TOBAGO TERRANE

The Tobago terrane is an extensive block of lithosphere in the southea stern corner of the boundary zone between the Caribbean and South Amer ica plates. The terrane is defined by its tectonic stratigraphy, which has five major aspects: (1) oceanic lithosphere of Cretaceous or earl ier ages; (2) a suprajacent complex of marine sedimentary rocks (volca nigenic and hemipelagic) and island-arc magmatic rocks of late Early a nd Late Cretaceous ages; (3) Paleogene island-are rocks; (4) Paleogene and early Miocene forearc-basin rocks, and (5) Neogene sedimentary co ver. The Tobago terrane is bounded by faults that include ages of moti on from the Cretaceous to the present. The Tobago terrane probably has translated a large distance relative to nearby South America and Trin idad and also has undergone motions relative to the Caribbean plate. T he Tobago terrane may have maintained coherency since inception as a f ragment, but a history of progressive amalgamation of similar basement blocks also is possible. Exposed and drilled rock units assigned to t he Tobago terrane include the Mejillones and Bocas complexes and supra jacent sediments of the Carupano Basin; the El Copey Formation of the Paria coast; the North Coast Schist and Cretaceous are rocks of Tobago ; the La Rinconada complex of Margarita; the Los Frailes basalt and re lated dikes of Margarita; and the Los Testigos magmatic are. Highlight s of the developmental history of the Tobago terrane include the follo wing: (1) formation of oceanic lithosphere over an uncertain period be fore similar to 120 Ma in Tobago but perhaps extending to as young as 90 Ma in Margarita; (2) underthrusting and underplating of the oceanic lithosphere in a subduction zone by continent-derived rocks of the Ar aya-Margarita terrane and deformation of the overriding lithosphere be fore similar to 90 Ma; (3) heterogenous uplift and cooling in the Earl y Cretaceous; (4) widespread island-are magmatism and related marine s edimentation, probably linked to the subduction of the Araya-Margarita terrane between Barremian and Santonian or later times; (5) coupled d evelopment of the Los Testigos magmatic are and the Caracolito forearc basin along the northern and central reaches, respectively, of the te rrane in Paleogene time, as related to subduction of the Atlantic ocea nic slab; (6) uplift and denudation of the western reach of the terran e in the Paleogene and of the southern half of the terrane in mid-Ceno zoic time; (7) overriding of and variable coupling to the Paria-Trinid ad terrane along the southern margin of the Tobago terrane (8) wedging into and possibly below the Barbados accretionary prism along the Tob ago terrane's eastern margin in Cenozoic time; (9) collision with and southward overriding. of the terrane complex above continental South A merica in the Miocene; and (10) denudation and extensional faulting of the elevated southern fringe of the Tobago terrane in late Neogene ti me.