COEVAL DEEPENING OF SUPRACRUSTAL SEDIMENTS AND ECLOGITE-FACIES METAMORPHISM OF SIALIC CRUST: RECORD OF CAMPANIAN COLLISION AT THE CARIBBEAN-NORTH AMERICAN PLATE BOUNDARY

Late Cretaceous collision of the southernmost portion of the North American plate is well recorded in both supracrustal and high-pressure metamorphic rocks. Mid-Cretaceous continental platform deposits are overlain by strata belonging to the late Campanian (~73 Ma) Globotruncanita calcarata biostratigraphic zone that contain fauna indicative of slope environment under the photic zone. These beds are covered by Maastrichtian–Danian flysch, which contains 75 ± 1 Ma volcanic cobbles. Whole-rock trace element concentrations show that the cobbles were derived from a mature arc, suggesting that the colliding block was the active Greater Antilles Arc. Onset of subsidence was contemporaneous with subduction and eclogite-facies metamorphism of the plate’s Mesoproterozoic–Jurassic sialic basement (Chuacús Complex). Cpx-Grt-Phg thermobarometry of gneiss-hosted eclogites indicates conditions at ~700–800 °C and ~2.1–2.4 GPa, implying continental subduction to >60 km depth. SHRIMP-RG dating of eclogite metamorphic zircon yielded a 75.5 ± 2 Ma age. Chondrite-normalized rare earth element patterns of zircon lack Eu anomalies and show depletions in heavy rare earths, consistent with a plagioclase-free, garnet-rich, eclogite-facies assemblage during zircon formation. Therefore, the Campanian age represents the timing of continental subduction, as confirmed by a 76 ± 16 Ma Sm/Nd mineral isochron of an eclogite band contained in orthogneiss. The above features indicate that during the Campanian the leading edge of the North American plate subducted under the Great Antilles island arc to near-UHP conditions. Several km north of the core of the collision zone, North America's continental platform subsided and was covered by flysch derived mainly from the hanging wall.