3D numerical modelling of the evolution of a restraining bend: the example of the Jamaican duplex system

Modelling strike-slip systems over geological timescales (> 1 Ma) and under high deformation (> 1) poses significant challenges. A primary difficulty arises because most of the displacement in these systems is horizontal, while the lithospheric strength is predominantly controlled by its vertically stratified rheological variations. As a result, two-dimensional models introduce substantial errors and are inadequate for capturing the complexities of strike-slip deformation. Furthermore, the inherently three-dimensional nature of the problem makes boundary conditions critical. To realistically simulate the horizontal sliding of two tectonic plates, the driving forces should ideally be applied far from the deformation zone, along boundaries parallel to the motion.

In this study we present new 3D numerical thermo-mechanical models using newly developed type of boundary conditions to simulate for the first-time strike-slip restraining bend systems evolving over more than 15 Myrs that we compare with the Jamaican segment of the Enriquillo-Plantain Garden Fault, one of the two strike-slip fault zones which mark the boundary between the Caribbean and the North America plates. This text-book example of compressional bend on a left-lateral wrench fault, uplifts topography in the Blue Mountains. It however displays sets of conjugate shear zones and tension faults which confer a little complexity in the natural example. To simulate the long-term deformation of the lithosphere, we use pTatin3d, a parallel finite element software that solves the equations governing the conservation of momentum and mass for an incompressible fluid with non-linear viscosities.

Models show the evolution from parallel strike-slip shear zones linking with P-shear around which positive flower structure develops. The evolution in time shows that the duplex system grows laterally with the development of new P-shear surrounded by thrust faults. Additionally, we provide the evolution in time and space of the topography, the 3-dimensional fault network and its structural analysis, the long-term slip-rate, and the stress regime of active faults. We finally compare the results to the observations of the morphostructures of the island.