Abstract

Structural field relationships, petrography and geochemical features of plagiogranites and associated intermediate (diorite) to mafic rocks (basalt and gabbro) of the Habana–Matanzas ophiolites in northern Cuba suggest that these felsic and mafic rock units represent a boundary case between forearc and volcanic arc ophiolite types. Subduction-related basalts can be subdivided into back-arc, back-arc to forearc, forearc and volcanic arc types. The majority of the basalts plot in the oceanic arc (as well as joint oceanic arc–continental arc) field of the Th/Yb–Nb/Yb diagram. The samples that classify as volcanic arc basalts plot in the continental arc field of the Th/Yb–Nb/Yb diagram and within the island arc tholeiite and boninite fields in the V–Ti diagram. The Habana–Matanzas plagiogranites and associated basalts, diabases and gabbros display significantly negative Ta–Nb anomalies and are depleted in heavy rare earth elements. 40Ar/39Ar whole-rock plateau ages of these plagiogranites reveal minimum crystallization ages of 98.11 ± 0.50 Ma, providing the first important time constraint for suprasubduction zone oceanic crust formation on the island of Cuba. Based on our petrogenetic modelling and geochemical characterization, we conclude that magmas of the plagiogranites and associated intermediate rocks of the Habana–Matanzas ophiolites were derived from partial melting of highly depleted, pre-existing crustal rocks (basalt and/or gabbro).

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