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Geochemistry of Compositionally Distinct Late Cretaceous Back-Arc Basin Lavas: Implications for the Tectonomagmatic Evolution of the Caribbean Plate

The Cretaceous Blue Mountain Inlier of eastern Jamaica contains the Bellevue lavas, which represent a Mid- to Late Campanian back-arc basin succession of tholeiitic volcanic rocks. The lavas are composed of basic/intermediate and intermediate/acidic subgroups that can be related by intraformation fractional crystallization. Trace element and Hf radiogenic isotope data reveal that the mantle component of the Bellevue magmas is consistent with derivation from a mantle plume (oceanic plateau) source region. Modeling indicates that the magmas formed by 10%–20% partial melting of an oceanic plateau mantle source comprising spinel peridotite that had previously undergone approximately 5%–7.5% prior melt extraction in the garnet stability field. Trace element and radiogenic isotope systematics suggest that the Bellevue mantle source region was contaminated with a slab-derived component from both the altered basaltic slab and its pelagic sedimentary veneer. The data from the Bellevue lavas support the plateau reversal model of Caribbean tectonic evolution, whereby subduction on the Great Arc of the Caribbean was to the northeast until the Caribbean oceanic plateau collided with the southern portion of the Great Arc in the Santonian (85.8–83.5 Ma), resulting in subduction polarity reversal and thus southwest-dipping subduction. This polarity reversal allowed oceanic plateau source regions to be melted beneath a new back-arc basin to the southwest of the Great Arc.