Geochemistry of Cretaceous magmatism in Eastern Cuba: recycling of North American continental sediments and implications for subduction polarity in the Greater Antilles paleo-arc

We present whole-rock major- and trace-element and Nd-Sr-Pb radiogenic isotope data for Cretaceous igneous suites from eastern Cuba. These rocks are related to the Greater Antilles paleo-island arc magmatism and have three different igneous styles. Group 1 consists of tholeiitic basalts and rare basaltic andesites that have normal mid-ocean ridge basalt (N-MORB)-like compositions similar to those found in back-arc basin basalts (TiO2 = 1.2-2.9wt%; La/Yb-( N) = 0.7-0.9, Th/Nb = 0.06-0.08, and initial Pb-208/Pb-204 = 37.65-3.74). Group 2 comprises basaltic and rare basaltic andesitic subvolcanic dykes with major- and trace-element and isotopic compositions similar to those of island arc tholeiites (TiO2 =0.7-1.4 wt%; La/Yb-(N) =0.6-0.9, Th/Nb = 0.06-0.68, and initial Pb-208/Pb-204 = 37.74-38.25). Group 3 is composed of low-Ti (TiO2 =0.3-0.9 wt%) calcalkaline igneous rocks that have an unambiguous subduction-related character (La/Yb-(N) = 1.1-5.0, Th/Nb = 0.35-1.55, and initial Pb-208/Pb-204 = 37.94-38.39). The parental magmas of the three groups formed by variable melting degrees (<5-25%) of spinel lherzolite, with more depleted mantle sources for Groups 2 and 3 than Group 1. The trace-element and radiogenic isotope compositions of primitive Group 3 samples are strongly bimodal. One subgroup of samples is characterized by low Ta/Yb (0.02-0.03) and Th/La (0.10-0.13), slightly subchondritic Nb/Ta (13.3-17.3), and relatively high initial Pb-206/Pb-204 (18.57-18.62) and is an element of(Nd) (7.6-9.4). The remaining primitive Group 3 samples have higher Ta/Yb (0.06-0.11) and Th/La (0.24-0.32), and highly subchondritic Nb/Ta (7.6-9.1), coupled with lower initial Pb-206/Pb-204 (18.24-18.29) and is an element of(Nd) (3.4-5.5). These signatures were induced by two distinct slab components that mainly reflect the contributions of Cretaceous Atlantic marine and North American continental sediments, respectively. Nb/Ta in the first subgroup was influenced by melting of rutile-bearing subducted crust, whereas in the second it was inherited from recycled continental sediments. The involvement of Atlantic and North American sediments in Cuban Cretaceous magmatism indicates that the Proto-Caribbean (North American-Proto Atlantic) lithosphere subducted beneath the Greater Antilles arc during the Late Cretaceous (pre-Campanian), consistent with geotectonic models involving onset of SW-dipping subduction beneath the Greater Antilles paleo-arc during the Aptian. The variable mantle source depletion and magnitude of the subduction component probably reflect different settings across the arc, from the arc front to a back-arc spreading ridge.