METAMORPHIC EVOLUTION OF SUBDUCTED HOT OCEANIC CRUST (LA COREA MELANGE, CUBA)

Thermobarometric estimates and predictions of theoretical and experimental isochemical P-T phase diagrams for epidote +/- garnet amphibolite blocks from the serpentinite melange of La Corea (eastern Cuba) indicate partial melting of subducted oceanic lithosphere occurred at peak metamorphic conditions of ca. 700 degrees C and 14 to 15 kbar. These anomalously high geothermal conditions suggest onset of subduction of young oceanic lithosphere of the Proto-Caribbean. The amphibolites have basaltic composition and MORB affinity. Partial melting produced tonalitic-trondhjemitic-granitic melts that crystallized at depth associated with the amphibolites. Calculated retrograde conditions for the amphibolites (450 degrees C and 8-10 kbar) indicate counterclockwise P-T paths during exhumation in the subduction channel, in agreement with published predictions on thermo-mechanical modeling of onset of subduction of young lithosphere. These findings have important consequences for the plate tectonic configuration of the Caribbean realm since they corroborate the existence of fragments of early subducted young oceanic lithosphere in the eastern Cuba melanges that indicate subduction of an oceanic ridge during mid-Cretaceous times.