Recycling in the subduction factory: Archaean to Permian zircons in the oceanic Cretaceous Caribbean island-arc (Hispaniola)

Abstract

Little mineralogical evidence is left of the recycling of continental and oceanic crust into the mantle at subduction zones. Zircon, because of its exceptional robustness, is probably the only surviving phase and the best mineral tracer of this global-scale process. This article combines new in-situ U-Pb dating and O and Hf isotope analyses on Cretaceous (co-magmatic) and pre-Cretaceous (inherited) zircons separated from Albian-Aptian arc-related igneous rocks from the Dominican Republic. The O and Hf systematics of Cretaceous zircons reflect derivation from predominantly juvenile sources and variable mixing with evolved melts, as expected for an oceanic island-arc. Inherited zircons yield U-Pb ages between 256 and 2923Ma (n=219). Most studied inherited zircons are Permian-Carboniferous, peaking at ca. 300Ma, and formed in continental crust to judge from mineral inclusions (including quartz, orthoclase, muscovite and apatite), δ18O (6.16 to 12.67‰) and εHf(t) (−11.9 to 1.12) values. Ordovician to Proterozoic zircons yield δ18O between 4.93 and 9.21‰ and εHf(t) between −19.9 and 8.5 and hence crystallized in equilibrium with either mantle-derived (juvenile) magmas or magmas derived from melting of supracrustal rocks. For Archean zircons, δ18O between 6.98 and 7.94‰ and εHf(t) between −18.5 and −1.6 might reflect contribution of supracrustal materials in the parent magmas. We suggest that arc magmas picked up the inherited zircon cargo from their mantle sources. Accounting paleogeographic and paleo-tectonic constraints, Mexican and Colombian terranes are identified as the potential primary (magmatic) and secondary (sedimentary) sources for the studied inherited zircons. We envisage that inherited zircons were transported downward to the mantle beneath the Caribbean plate as detrital grains on top of the subducting Proto-Caribbean and/or Pacific slabs.