Structural development of a high-pressure collisional accretionary wedge: The Samaná complex, Northern Hispaniola

Abstract

The Samaná metamorphic complex exposes a segment of a high-pressure collisional accretionary wedge, built during Caribbean island arc-North America continental margin convergence. Combined detailed mapping, structural and metamorphic analysis, and 40Ar/39Ar geochronology show that the deformation can be divided into five main events. Early subduction-related D1 deformation and high-P/low-T M1 metamorphism under lawsonite blueschist (325–425°C/12–18 kbar; Rincon Marbles and Santa Bárbara Schists lower structural nappes) and eclogite facies conditions (425–450°C/18–20 kbar; Punta Balandra upper structural nappe), was followed by M2 decompression and cooling in the blueschist facies conditions during D2 folding, thrusting and nappe stacking. 40Ar/39Ar plateau ages and T-t/P-t estimations revealed Late Eocene to earliest Miocene retrograde M2 metamorphism in the different nappes for a consistent D2 top-to-the-ENE tectonic transport, which suggests a general northeastward progradation of deformation. The D3 event substantially modified the nappe stack and produced open to tight folds with amplitudes up to kilometer-scale and the D4 ductile to brittle normal shear zones and faults, and related subhorizontal folding, record a late extensional deformation, which also affects the whole nappe pile. Non-penetrative D3 and D4 fabrics indicate M3 cooling in and under the M3 greenschist-facies conditions. From the Miocene to the Present, the nappe pile was cut and laterally displaced by a D5 sinistral strike-slip and reverse fault system associated with the Septentrional fault zone.