History of eruptive magmatism in the Caribbean Basin

The paper discusses spatial and temporal correlations of the distribution o f volcanic ash beds and the compositional evolution of pyroclastic material contained in the Mesozoic and Cenozoic sedimentary cover of the Caribbean Basin with the tectonics and magmatism of regional island-arc systems. The calculated volumes and deposition rates of pyroclastics in various stratigr aphic units of the Cretaceous and Cenozoic make it possible to reveal an un systematic periodicity of eruptive magmatism pulses in the Late Cretaceous, Early Eocene, Early Miocene, and Paleogene. These pulses complicated the " background" ash deposition, with the latter testifying that local eruptive volcanic processes and associated tectonic motions of continental and ocean ic blocks continuously proceeded in fault and subduction zones. It was esta blished that, starting from the Late Cretaceous (Turonian-Coniacian) to the present, the composition of the pyroclastic material systematically varied from predominantly basaltic to predominantly silicic (dacitic and rhyoliti c). This phenomenon is accounted for by an increase in the volumes of terri genous sediments, which were transported to the magma generating zones by p lates. The effect of continental terrigenous sediments on the composition o f Caribbean island-arc volcanics is confirmed by the fact that the Sr-87/Sr -86 ratio increases toward South America. The Late Cretaceous pyroclastics have smaller admixture of terrigenous sedimentary material and were derived mainly from oceanic basalts. These compositional trends of pyroclastics ar e not only typical of the Caribbean Basin but can also be discerned worldwi de. Our model for the genesis of the composition of the pyroclastic materia l is also applicable to other island-arc systems. The volcanic cycles are c orrelated with phases of tectogenesis and other geologic events.