Fault kinematics, exhumation, and morphological signature of the Septentrional sliver (Dominican Republic)

Forearc slivers are important tectonic features due to their sensitivity to the dynamic and tectonic processes at subduction zones. For example, slivers may exhibit lateral, vertical, and rotational motions due to the subduction of buoyant features or structural highs on the downgoing plate. The Septentrional sliver along the Northern Caribbean Plate Boundary (NCPB) provides a natural example of the formation and evolution of a forearc domain during plate reorganization accompanied by multiple indentation episodes with progressive along-strike variation from a subduction to transform margin. The sliver was initially delineated in the Miocene with the formation of the Septentrional Fault Zone (SFZ), one of the two major strike-slip systems comprising the NCPB, facilitating the uplift of the Cordillera Septentrional. However, our present understanding of the relationship between the time-varying kinematics of the SFZ and the uplift and exhumation of the Cordillera Septentrional is limited. To address this, we conduct zircon and apatite (U-Th)/He analyses on in-situ and detrital samples gathered across the Cordillera Septentrional and combine these data with along-strike kinematic measurements, topographic analyses, and new field observations. Zircon and apatite He dates range from 55 to 2.7 Ma, with detrital dates indicating limited burial and resetting. The youngest apatite He dates are proximal to major structures, indicating increased near-field exhumation. In-situ dates along the SFZ are constrained to 7.5±0.7 Ma, with dates increasing to >25 Ma to the north. Combined with lithostratigraphy, date distributions correspond with two main exhumation pulses beginning in the late Eocene and late Miocene. The recent pulse of exhumation occurred by ~10 Ma at rates up to 0.3 mm/yr, leading to >2 km of vertical motion. Along the Septentrional fault zone, slickenline orientations, topographic analyses, and exhumation rates show substantial west-to-east variability corresponding to a change from transpression to transtension. In the west, the Cordillera is characterized by rugged topography, a quasi-stationary drainage divide, oblique to compressional slip indicators, and positive flower structures. To the east, fault surfaces show oblique to extensional slip indicators, a low-relief northeast tilted surface, a drainage divide propagating northward, and higher total exhumation. We propose that along-strike heterogeneity is due to time-varying boundary conditions imposed by the subduction of the buoyant carbonate Bahamas platform overlying thickened oceanic lithosphere. These effects result from three main factors: (1) fault geometry, (2) the subduction of high-standing ridges on the Bahamas Platform in the west, and (3) the progressive uncoupling of the plate interface due to the eastward translation of NCPB blocks past the indenter. Overall, this study provides insight into the evolution of the NCPB and the consequences of forearc indentation and along-strike complexity of the subduction-transform margin.