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–Pbradiogenic isotope data for Cretaceous igneous suites from easternCuba. These rocks are related to the Greater Antilles paleo-islandarc magmatism and have three different igneous styles. Group1 consists of tholeiitic basalts and rare basaltic andesitesthat have normal mid-ocean ridge basalt (N-MORB)-like compositionssimilar 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 ²⁰⁸Pb/ ²⁰⁴Pb = 37·65–37·74).Group 2 comprises basaltic and rare basaltic andesitic subvolcanicdykes with major- and trace-element and isotopic compositionssimilar to those of island arc tholeiites (TiO₂ = 0·7–1·4wt%; La/Yb_(N) = 0·6–0·9, Th/Nb = 0·06–0·68,and initial ²⁰⁸Pb/ ²⁰⁴Pb = 37·74–38·25).Group 3 is composed of low-Ti (TiO₂ = 0·3–0·9wt%) calcalkaline igneous rocks that have an unambiguous subduction-relatedcharacter (La/Yb_(N) = 1·1–5·0, Th/Nb = 0·35–1·55,and initial ²⁰⁸Pb/ ²⁰⁴Pb = 37·94–38·39).The parental magmas of the three groups formed by variable meltingdegrees (< 5–25%) of spinel lherzolite, with more depletedmantle sources for Groups 2 and 3 than Group 1. The trace-elementand radiogenic isotope compositions of primitive Group 3 samplesare strongly bimodal. One subgroup of samples is characterizedby 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 ²⁰⁶Pb/²⁰⁴Pb (18·57–18·62)and _Nd (7·6–9·4). The remaining primitiveGroup 3 samples have higher Ta/Yb (0·06–0·11)and Th/La (0·24–0·32), and highly subchondriticNb/Ta (7·6–9·1), coupled with lower initial²⁰⁶Pb/²⁰⁴Pb (18·24–18·29) and _Nd (3·4–5·5).These signatures were induced by two distinct slab componentsthat mainly reflect the contributions of Cretaceous Atlanticmarine and North American continental sediments, respectively.Nb/Ta in the first subgroup was influenced by melting of rutile-bearingsubducted crust, whereas in the second it was inherited fromrecycled continental sediments. The involvement of Atlanticand North American sediments in Cuban Cretaceous magmatism indicatesthat the Proto-Caribbean (North American-Proto Atlantic) lithospheresubducted beneath the Greater Antilles arc during the Late Cretaceous(pre-Campanian), consistent with geotectonic models involvingonset of SW-dipping subduction beneath the Greater Antillespaleo-arc during the Aptian. The variable mantle source depletionand magnitude of the subduction component probably reflect differentsettings across the arc, from the arc front to a back-arc spreadingridge. KEY WORDS: eastern Cuba; Greater Antilles paleo-island arc; mantle source depletion; Nb/Ta fractionation; slab component