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Blueschist metamorphism and deformation on the Samana Peninsula; A record of subduction and collision in the Greater Antilles

By
James Joyce
James Joyce
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Published:
January 01, 1991

The Samana Peninsula exposes part of a belt of metamorphic rocks that lie between late Mesozoic-Early Tertiary island-arc rocks of Hispaniola and Puerto Rico and carbonate rocks of the Bahama Platform. The peninsula is composed of pelitic, carbonate, and mafic volcanic rocks deformed and metamorphosed under low-temperature and high-pressure conditions and unconformably overlain by middle to Late Tertiary shallow-water sedimentary rocks. Three metamorphic zones are recognized in the complex: Zone I covers most of the peninsula and is characterized by lawsonite-albite assemblages; Zone II and the Punta Balandra Zone are limited to interlayered marble and schist along the southeast coast; Zone II mafic rocks are characterized lawsonite-actinolite-glaucophane blueschist assemblages. The Punta Balandra Zone mafic rocks exhibit epidote/clinozoisite-garnet-glaucophane blueschist assemblages and epidote/clinozoisite-garnet-omphacite eclogite assemblages.

Geothermometer and geobarometer calculations based on mineral analyses and the coexistence of lawsonite-zoisite-paragonite-quartz suggest minimum temperatures and pressures of 430° to 480°C at 10 to 12 kbar for the formation of the Punta Balandra Zone blueschists and eclogites. Radiometric ages indicate the blueschist and eclogite crystallization commenced by 80 Ma.

The prograde metamorphism and deformation (D1) that produced layer parallel schistosity, foliation, glaucophane lineation, and localized occurrence of eclogite are interpreted as products of accretion and underplating in a subduction complex or collision zone. The second deformation formed tight to isoclinal folds and is interpreted as a product of northeast-directed thrusting. Following the second deformation, Zone II and Punta Balandra Zone rocks were overprinted by greenschist assemblages. Phengite K-Ar ages suggest that the thrusting and greenschist overprinting occurred before 40 to 37 Ma. Middle to Late Tertiary shallow-water limestones unconformably overlie the metamorphic rocks and mark the final emergence of the metamorphic rocks to the surface. These rocks show little evidence for deformation other than fracturing and uplift. Latest Tertiary conglomerate and limestones flanking the southern margin of the peninsula are strongly tilted and faulted. The influx of the coarse-grained sediment and the deformation were probably due to uplift along the Septentrional-Northern Samana Bay faults since late Miocene time. Left-lateral motion along the Septentrional-Northern Samana Bay fault may have displaced Samana westward relative to Hispaniola and Puerto Rico.

The metamorphic rocks of the Samana Peninsula are interpreted to represent sedimentary and oceanic igneous rocks offscraped and underplated onto a subduction complex. The largely carbonate composition and the occurrence of oolitic dolomites in the metamorphic complex suggest that a carbonate bank may have collided with the Greater Antilles subduction zone. The Samana metamorphic rocks may represent part of a collision zone between the Bahama Platform and the Greater Antilles.

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GSA Special Papers

Geologic and Tectonic Development of the North America-Caribbean Plate Boundary in Hispaniola

Paul Mann
Paul Mann
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Grenville Draper
Grenville Draper
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John F. Lewis
John F. Lewis
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Geological Society of America
Volume
262
ISBN print:
9780813722627
Publication date:
January 01, 1991

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