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Fifty-five-million-year history of oceanic subduction and exhumation at the northern edge of the Caribbean plate (Sierra del Convento mélange, Cuba)

Abstract:

Petrological and geochronological data of six representative samples of exotic blocks of amphibolite and associated tonalite-trondhjemite from the serpentinitic mélange of the Sierra del Convento (eastern Cuba) indicate counterclockwise P-T paths typical of material subducted in hot and young subduction zones. Peak conditions attained were ∼750 °C and 15 kbar, consistent with the generation of tonalitic partial melts observed in amphibolite. A tonalite boulder provides a U-Pb zircon crystallization age of 112.8 ± 1.1 Ma, and Ar/Ar amphibole dating yielded two groups of cooling ages of 106-97 Ma (interpreted as cooling of metamorphic/magmatic pargasite) and 87-83 Ma (interpreted as growth/cooling of retrograde overprints). These geochronological data, in combination with other published data, allow the following history of subduction and exhumation to be established in the region: (i) a stage of hot subduction 120-115Ma, developed upon onset of subduction; (ii) relatively fast near-isobaric cooling (25 °C Myr-1) 115-107 Ma, after accretion of the blocks to the upper plate lithospheric mantle; (iii) slow syn-subduction cooling (4 °C Myr-1) and exhumation (0.7 km Myr-1) in the subduction channel 107-70 Ma; and (iv) fast syn-collision cooling (74 °C Myr-1) and exhumation (5 km Myr-1) 70-60 Ma. © 2009 Blackwell Publishing Ltd.