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 (D 1 ) 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.

Newly available seismic reflection data are applied to an interpretation of the Cibao basin of Hispaniola. The data include multichannel seismic reflection profiles from Samana Bay and the central part of the Cibao Valley, and single-channel seismic profiles from the western offshore extension of the Cibao Valley and the Windward Passage. A single track of GLORIA imagery through the Windward Passage is also used. The data in Samana Bay reveal a major, active, easterly oriented normal fault (transcurrent?) and a significant increase in sedimentation from the north, which probably began during Miocene to Pliocene time. A seismic reflection line in the central part of Cibao Valley demonstrates that the sedimentary material in the valley is at least 5 km thick, with the thickest section in the north adjacent to the Septentrional fault. The southern margin of the Cibao Valley appears to be the locus of a hingeline, although minor faults may be present. The oldest sedimentary basin fill overlying Cretaceous basement is probably of middle Miocene age based on outcrops of rock. At the western end of the Cibao Valley, the Septentrional fault curves northwesterly before going offshore. In addition, the Tortue fault, which extends offshore along the north coast of Haiti, is an extension of either the Guayubin-Hispaniola fault zones or is a southwestern branch of the Septentrional fault. It can be identified on the sidescan sonar images in Windward Passage.