From Aptian Onset to Danian Demise of Subduction along the Northern Margin of the Caribbean Plate (Sierra del Convento Melange, Eastern Cuba)
The serpentinite-matrix melange of the Sierra del Convento, eastern Cuba, represents an oceanic subduction channel related to Mesozoic subduction in the Caribbean realm which provides evidence for a long-lasting history of subduction, accretion, melange formation, and uplift, and for Aptian onset of subduction in the region. Exotic blocks of MORB-derived plagioclase-free epidote±garnet amphibolite followed a hot subduction-related prograde P-T path, reaching ca. 750 °C, and 14-16 kbar at peak conditions. Fluid flux at this stage triggered melting of the amphibolites to yield peraluminous tonalitic-trondhjemitic melts, which appear intimately associated with the amphibolites. Trondhjemitic-granitic varieties richer in K2O suggest the local participation of a sedimentary source, likely diluted through the infiltrating fluid. Calculated conditions for the magmatic assemblages (plagioclase, quartz, epidote, ±paragonite, ±pargasite, ±muscovite) of the siliceous rocks yield pressures of ca. 15 kbar, indicating crystallization at depth in the subduction environment. SHRIMP U-Pb zircon dating of two granitoid samples gives crystallization ages of 113-114 Ma. Partial melting of subducted oceanic crust in eastern Cuba is unique in the Caribbean realm and is interpreted as the result of onset of subduction of young oceanic lithosphere during the Aptian (ca. 120 Ma), in agreement with regional geological data. Calculated P-T conditions for the retrograde blueschist-facies overprints present in all rocks indicate counterclockwise P-T paths during exhumation in a colder, syn-subduction scenario. 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). The above P-T-t data and additional ages of other rocks from the area suggest the following stages of evolution:(a) hot subduction during 120-115 Ma with heating and burial rates of 150 °C/Ma and 11 km/Ma, respectively, developed shortly after onset of subduction of young oceanic lithosphere; (b) relatively fast near-isobaric cooling (25 °C/Ma) during 115-107 Ma, developed after accretion of the blocks to the upper plate mantle; (c) slow syn-subduction cooling (4 °C/Ma) and exhumation (0.7 km/Ma) in the subduction channel in a colder (mature) subduction environment during 107-70 Ma, and d) fast cooling (70 °C/Ma) and exhumation (5 km/Ma) during 70-65 Ma, when arc-continent collision occurred and subduction terminated in the region.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 8170 Subduction zone processes (1031;