ALBERT

Description: Within the last decade, modern petrological and geochronological methods in combination with detailed studies of the field geology have allowed the reconstruction of tectonic processes in the northwestern part of the Caribbean Plate. The development of an oceanic Proto-Yucatan Basin can be traced from the Late Jurassic to the Mid-Cretaceous. From the Mid-Cretaceous onward, an interaction of this basin with the Caribbean Arc can be observed. Geochronological data prove continuous magmatic activity and generation of HP mineral suites in the Caribbean Arc from the Aptian to the Campanian/Maastrichtian. Magmatism ceased at least in onshore central Cuba at about 75 Ma, probably as the southern edge of the continental Yucatan Block began to interact with the advancing arc system. Similarly, the youngest recorded ages for peak metamorphism of high-pressure metamorphic rocks in Cuba cluster at 70 Ma; rapid uplift/exhumation of these rocks occurred thereafter. After this latest Cretaceous interaction with the southern Yucatan Block, the northern Caribbean Arc was dismembered as it entered the Proto-Yucatan Basin region. Because of the continued NE-directed movement, Proto-Yucatan Basin sediments were accreted to the arc and now form the North Cuban fold and thrust belt. Parts of the island arc have been thrust onto the southern Bahamas Platform along the Eocene suture zone in Cuba. Between the arc's interaction with Yucatan and the Bahamas (c. 70 to c. 40 Ma), the Yucatan intra-arc basin opened by extreme extension and local seafloor accretion between the Cayman Ridge (still part of Caribbean Plate) and the Cuban frontal arc terranes, the latter of which were kinematically independent of the Caribbean. Although magmatism ceased in central Cuba by 75 Ma, traces of continuing Early Palaeogene arc magmatism have been identified in the Cayman Ridge, suggesting that magmatism may not have ceased in the arc as a whole, but merely shifted south relative to Cuba. If so, a shallowing of the subduction angle during the opening of the Yucatan Basin would be implied. Further, this short-lived (?) Cayman Ridge arc is on tectonic strike with the Palaeogene arc in the Sierra Maestra of Eastern Cuba, suggesting south-dipping subduction zone continuity between the two during the final stages of Cuba-Bahamas closure. After the Middle Eocene, the east-west opening of the Cayman Trough left the present Yucatan Basin and Cuba as part of the North American Plate. The subduction geometry, P-T-t paths of HP rocks in Cuban melanges, the time of magmatic activity and preliminary palaeomagnetic data support the conclusion that the Great Antillean arc was initiated by intra-oceanic subduction at least 900 km SW of the Yucatan Peninsula in the ancient Pacific. As noted above, the Great Antillean Arc spanned some 70 Ma prior to its Eocene collision with the Bahamas. This is one of the primary arguments for a Pacific origin of the Caribbean lithosphere; there simply was not sufficient space between the Americas, as constrained by Atlantic opening kinematics, to initiate and build the Antillean (and other) arcs in the Caribbean with in situ models.

Description: An elemental and radiogenic isotope study of Cretaceous island arc rocks on Tobago, West Indies, reveals the magmatic processes taking place at the eastern edge of the Pacific-derived Caribbean Plate during development of the Greater Antilles Arc. The ~110–103 Ma Volcano-Plutonic Suite comprises the ultramafic–intermediate Tobago Pluton and genetically related Tobago Volcanic Group. The volcanic rocks (breccias, tuffs, and mafic–intermediate lavas) have undergone shallow-level fractional crystallization involving plagioclase, clinopyroxene, olivine, and Fe–Ti oxides, but also preserve trace element evidence for ‘cryptic’ amphibole fractionation. The suite is inferred to have formed from a spinel lherzolite mantle wedge source fluxed largely by slab- and recycled volcanogenic sediment-derived fluids. A tonalitic mega-dyke intruding the pluton resembles high-silica adakites, and geochemical constraints indicate a likely origin by partial melting of the arc crust. A mafic dyke swarm (~103–91 Ma) is partly coeval with the volcanic rocks, but some, perhaps the youngest dykes, are derived from isotopically distinct arc mantle sources compared with the volcanic rocks. Rare Nb-enriched and high-Nb dykes may relate to melting of a high field strength element-enriched source. Current Caribbean tectonic models involve the continuation of east-dipping Farallon Plate subduction beneath the proto-Caribbean seaway either until an Early Cretaceous initiation of proto-Caribbean subduction, or collision of the Caribbean Oceanic Plateau with the Greater Antilles Arc at ~90–80 Ma. Both models may be compatible with the tectono-magmatic history of Tobago, wherein Tobago is thought to have detached from the fore-arc of the Caribbean arc system during Eocene intra-arc extension, the growth of the Grenada Basin, and inception of the Lesser Antilles Arc. Tobago- or La Désirade-like Mesozoic arc crust underlies much of the present-day Lesser Antilles Arc and not, as has recently been proposed, portions of the plume-derived Caribbean Oceanic Plateau.

Description: During the last century, three different ways of interpreting the tectonic evolution of the Gulf of Mexico and the Caribbean have been proposed, taking into account the Bailey Willis School of a permanent pre-Jurassic deep sea basin, the Edward Suess School of a subsided continental terrain, and the Alfred Wegener School of continental separation. The present investigation is concerned with an outline of an interpretation which follows that of Pindell and Dewey (1982). An attempt is made to point out ways in which the advanced hypotheses can be tested. The fit of Africa, North America, and South America is considered along with aspects of relative motion between North and South America since the early Jurasic. Attention is given to a framework for reconstructing Caribbean plate evolution, the evolution of the Caribbean, the plate boundary zones of the northern and southern Caribbean, and the active deformation of the Caribbean plate.