Relict abyssal mantle in a Caribbean forearc ophiolite (Villa Clara, central Cuba): petrogenetic and geodynamic implications

Abstract

ABSTRACT The ophiolitic Villa Clara serpentinite-matrix mélange, central Cuba, forms part of the large ophiolitic belt of the Greater Antilles. The composition of ultramafic and mafic rocks allows classifying them into two main groups, revealing a complex multi-stage formation of oceanic lithosphere in varied tectonic settings: i) group 1 matches fertile MORB-like mantle typical of abyssal/transform fault peridotites, while ii) group 2 shows characteristics of refractory mantle-wedge forearc peridotites. These features are consistent with moderate extent of partial melting (4–8%) of depleted mantle at a mid-ocean ridge setting that created residual abyssal peridotite (group 1) and intense remelting (14–18%) of the latter in a forearc setting that created highly refractory peridotite (group 2). The elemental and isotopic characteristics of groups 1 and 2 serpentinites denote the influx of fluids evolved from the subducting slab. Mafic rocks appear as variably sized tectonic blocks within serpentinite that underwent variable alteration at low pressure. Immobile element concentrations allow identifying two main groups: i) group 1 is consistent with forearc basalts formed during the second stage of melting of (abyssal) peridotite, while ii) group 2 has a compositional pattern like island-arc tholeiitic basalts. A geodynamic evolution from abyssal to forearc settings is presented to explain the nature of the oceanic lithosphere of the Villa Clara ophiolitic bodies and ensuing serpentinization and mélange formation. This model may explain other ophiolitic bodies of the Caribbean arc in Cuba, Dominican Republic and Puerto Rico and elsewhere formed in abyssal/transform fault or forearc settings.