The role of Paleogene magmatism in the evolution of the northern Caribbean margin: The Sierra Maestra (southern Cuba)

The northern Caribbean area has a complex tectonic framework as a result of collision of the Cretaceous Greater Antilles arc against the Bahamas Platform, and the strike-slip tectonic regime of the Cayman fault zone that has been active since late Middle Eocene. The Sierra Maestra is an extension of the Cayman Ridge and occupies essential position in between the remnants of the Greater Antilles arc accreted terranes and the Cayman strike-slip belt. Previous biostratigraphic work indicates that the Sierra Maestra formed as an independent volcanic arc south of the Greater Antilles arc.; Trace elements show that the geochemical signature of the Sierra Maestra is intermediate between that of a typical oceanic arc and N-MORB and chemically bears strong similarity to primitive oceanic areas and related rifting environments such as the western Lau basin. The subduction component, both as slab derived fluids and sediments input, was minimal. Lead isotope ratios for the Sierra Maestra are homogeneous, indicating the existence of a single magma source. There is a significant overlap between the isotopic ratios of the Sierra Maestra and the Cretaceous island arc tholeiites of Puerto Rico indicating that the Paleogene arc rocks have a similar mantle source. The magmatism evolved by a combination of fractionation and mixing. The absolute age for the magmatism in the Sierra Maestra is constrained by U-Pb zircon age determinations to the interval 46–56 Ma, in agreement with the age inferred from the biostratigraphic work: from early Paleocene to Middle Eocene. Field observations indicate that the volcanism occurred in a submarine environment, at depths estimated between 2000 and 500 m. Volcanic activity was very intense and predominantly explosive, and produced thick pyroclastic sequence that makes up about 75% of the whole Sierra Maestra volcanic succession.; It is concluded that the Sierra Maestra represents a very immature oceanic arc environment, either a rejuvenation of the Greater Antilles arc (roll back of the older arc hinges), or an “infant arc”, i.e. the beginning stage of sinking lithosphere, and never evolved beyond the first stages of subduction.