Geodynamic evaluation of the pacific tectonic model for chortis block evolution using 3D numerical models of subduction

Past position and subsequent tectonic evolution of the Chortis Block represents one of the major uncertainties related to the geodynamic evolution of southern Mexico and northern Central America. This uncertainty has led to different hypotheses and evolutionary models based on tectonic, geological and paleographic studies that attempt to explain the origin and paleoposition of the Chortis Block. Among these models, a challenging hypothesis suggests the Chortis Block originates from a west-southwest position in the Pacific rather than attached to the Mexican margin. Additionally, this model proposes a high rate (200 km/20 Myr) of trench erosion along the Mexican margin just north of the present-day Chortis Block. In the Pacific model, the Chortis Block is being pushed eastward by the subduction movement of the Farallon and Cocos oceanic plates, and is finally captured by the Caribbean plate. In this study, the evolution of subduction along the Mexican and Central America margins is investigated numerically taking into account kinematic reconstruction of the Pacific model. The main goal is to investigate validity of the Pacific model for Chortis Block evolution by comparing our predicted slab geometries with present-day tomographic images. The kinematic 3D numerical models are integrated 45 Myr in time and use a mantle reference frame for tectonic plate evolution of the study area. These models generate subducting plate geometries that are only partial consistent with what is observed from seismic tomography, they reproduce realistic slab geometries only for the region located beneath the North America Plate, where the Cocos slab is flat at shallow depths and also stagnates along the mantle transition zone. On the other hand, for the region located beneath the Chortis Block the slab penetrates vertically through the upper mantle and even curls back in the upper portion of the lower mantle, a geometry that is inconsistent with seismic tomography images which shows the presence of east-dipping slab that tends to stagnate at 1000 km depth. This study indicate that the Pacific model is not an appropriate hypothesis for explaining the Chortis Block origin, and future studies should focus on alternative tectonic models.