Vertical deformation along the northern Caribbean plate boundary zone, Haiti

Oblique plate convergence results in complex deformation patterns, making tectonic and geodynamic interpretations challenging. North of Haiti, oblique convergence occurs between the Caribbean and the North American plates. In this area, the 20° oblique EN E -WSW convergence of the North American plate is partitioned between the underthrust of the Bahamas carbonate banks beneath the Caribbean plate along the E -W-trending North Hispaniola reverse Fault Zone (NHFZ), and further south by the E -W-trending, sinistral Septentrional Oriente Fault Zone (SOFZ). Between the NHFZ and the SOFZ, an E-W-trending accretionary prism accommodates part of the obliquity. South of the SOFZ, the oblique convergence is accommodated by NW-trending folds and thrusts across Haiti, and by the southern E -W-trending sinistral Enriquillo-Plantain-Garden Fault Zone (EPGFZ). This study aims to characterize Quaternary deformation across the SOFZ, by analyzing uplifted coastal terraces located north and south of the fault zone. We present a detailed mapping of these geomorphological markers and quantify spatiotemporal variations in their elevations. The results reveal inactive reverse faults and folds, as well as contrasting deformation patterns of coastal terraces on either side of the SOFZ, with significant spatial and temporal uplift gradients associated with superimposed long-wavelength tilting and short-wavelength folding. North of the SOFZ, the eastward uplift gradient indicates that the accretionary prism accommodates much of the oblique convergence to the East. South of the SOFZ, the southward tilt of the coastal terraces in the northwestern peninsula of Haiti may reflect spatial variations in the structure of the underthrusting North American plate, with thicker continental crust to the west producing an isostatic effect beneath the Caribbean plate. This process could generate long-wavelength uplift of the latter as the slab is underthrusting below the plate boundary. Short-wavelength NW-trending folding overlaps this long-wavelength uplift pattern and, to a lesser extent, accommodates the shortening produced by the plate convergence.