Paper No. 275-5
Presentation Time: 9:05 AM
METAMORPHIC COMPLEXES IN CUBA: P-T-T EVOLUTIONS, TECTONIC SETTINGS AND GEODYNAMIC IMPLICATIONS
Geochronologic data indicate continuous formation of metamorphic complexes in Cuba since 130 to ca. 50 Ma related to formation of oceanic island arc lithosphere, coeval subduction of oceanic and transitional lithosphere and subsequent arc-passive margin collision. Tectonic blocks of low-pressure amphibolite (ca. 5-10 km depth, 130-125 Ma) within serpentinite mélanges associated with the ophiolitic units 1200 km along the island (e.g., Cajálbana, La Tinta) represent mafic bodies of diabasic/gabbroic rocks that intruded the mantle in a fore-arc setting during subduction initiation. Tectonic blocks of MORB blueschist and eclogite (up to 60-70 km depth; 125-70 Ma) and fore-arc antigorite-serpentinite within serpentinite mélanges document fragments of the subduction channel (e.g., Bahía Honda, Santa Clara, Holguín). P-T conditions characteristic of warm subduction point to moderately young thermal age of the subducting lithosphere. Oscillatory zoning is common in garnet of the earliest eclogite blocks suggesting tectonic complexities during the early stage of subduction. Migmatitic MORB garnet amphibolite and anatectic trondhjemite-tonalite rocks (50 km depth, 700-750 ºC; 115-105 Ma) from eastern Cuba Sierra del Convento and La Corea mélanges followed counter-clockwise P-T paths and document hot thermal gradient during subduction, likely of an oceanic ridge. Amphibolite and orthogneiss (Mabujina Complex; ca. 20 km depth, up to 650-700 ºC; 90-92 Ma) of island arc protoliths occur tectonically below the volcanic arc unit of central Cuba. They are interpreted as the result of a discrete event of intra-arc collision involving an exotic arc block. In eastern Cuba, the Güira de Jauco amphibolitic complex (ca. 30 km depth, 650 °C, 85 Ma) represents a metamorphic sole below the Moa-Baracoa ophiolitic unit. It documents inception of a new subsidiary subduction zone in the back-arc region of the Caribbean arc previous to ophiolite obduction. Coherent eclogite-, blueschist-, greenschist- and amphibolites-facies complexes involving passive margin sedimentary-magmatic sequences (Cangre, Pinos, Escambray and Asunción terranes/complexes) and volcanic arc sections (Purial complex) document a major event of subduction/accretion at 75-65 Ma shortly before Paleogene arc-passive margin collision.