Cretaceous island-arc rocks of the Caribbean island-arc system have been exposed by Cenozoic faulting in the Cordillera Oriental in eastern Hispaniola. High-K 2O intermediate to felsic volcanic rocks (Loma la Vega volcanics) are interbedded with marine epiclastic sedimentary rocks and tuffs (Las Guajabas tuffs) and unconformably overlie pre-Aptian sedimentary rocks, low-K 2O volcanic rocks (Guamira volcanics) and a granodioritic to tonalitic intrusion (El Valle pluton). The petrology and geochemistry of these units, in conjunction with regional stratigraphic data, are used to speculate on the tectonics of the newly developing Caribbean island-arc system during Early and Late Cretaceous time. The Loma la Vega volcanics are characterized by the presence of large phenocrysts of sanidine, and minor amounts of clinopyroxene, opaque oxides, and rare leucite in a devitrified matrix of chlorite and clay. Although the volcanic rocks have undergone some low-temperature alteration/ metamorphism, which redistributed some major elements and large-ion-litho-phile trace elements, the high-field-strength elements, rare-earth elements, and radiogenic isotopes appear to have been minimally affected. Based on abundances of the relatively immobile elements, trace-element enrichment patterns and isotopic compositions, the Loma la Vega volcanics are considered part of the high-K, calc-alkaline (CA) or shoshonitic island-arc volcanic series. In contrast, pre-Aptian (Early Cretaceous?) volcanic and plutonic rocks of the underlying Los Ranchos Formation have chemical characteristics similar to rocks in the island-arc tholeiitic or “primitive island-arc” (PIA) series that form coeval and along-strike sections of the Early Cretaceous Caribbean island arc in other parts of present-day Hispaniola, Cuba, Puerto Rico and the Virgin Islands. An abrupt and regional change in composition from island-arc tholeiites to high-K, calc-alkaline rocks is coincident with a hypothesized reversal in subduction polarity in pre-Aptian time. As inferred from previously published tectonic models, polarity reversal may have been triggered by attempted subduction of the Caribbean oceanic plateau beneath this segment of the Caribbean island arc. The observed magmatic and tectonic effects of the proposed Cretaceous Caribbean arc reversal are similar to the better documented Neogene subduction reversal event in the Solomon Islands arc in the southwest Pacific.