TECTONIC ORIGIN AND EVOLUTION OF THE CENTRAL AMERICAN HIGH-PRESSURE/LOW-TEMPERATURE SERPENTINITE MéLANGES: A NEW 3D GEODYNAMIC SCENARIO

In northern Central America three distinct high-pressure/low-temperature (HP/LT) serpentinite-matrix mélange belts occur. Two crop out along the Motagua fault zone; the North Motagua Mélange (NMM) and the South Motagua Mélange (SMM) in Guatemala. The southern most belt is the Siuna Serpentinite Mélange (SSM) in north-eastern Nicaragua and marks the boundary between continental and oceanic crust in southern Central America.

The SSM occurs as small tectonic window ~40 km long. This mélange underwent a single HP/LT event at ~139 Ma characterized by MORB and IAT protoliths, which indicate subduction and subsequent collision of a Middle Jurassic island arc during the Late Jurassic-Berriasian time. The SMM is exposed in a discontinuous belt ~60 km long. The occurrence of lawsonite eclogite and jadeitite blocks suggests a cold and wet subduction zone. This mélange records HP/LT crystallization, at ~154 Ma, ~144-132 Ma and ~125-113 Ma and formed during Late Jurassic subduction and Early Cretaceous final collisional event. In contrast, the NMM consists of mélange slices thrust onto the Maya block, and it extends fragmentally over 200 km. This mélange contains eclogite, garnet amphibolite and jadeitite blocks that record two different HP/LT events, a metamorphic peak of ~131-126 Ma and a subduction/exhumation ages of ~95-65 Ma. These ages indicate an initial collisional event follow by the reworking of HP/LT blocks until a final collision during the Late Cretaceous.

All of these data together with the distribution, composition and age of the igneous activity as well as sedimentation, structural geology, paleomagnetic data and geophysical structure of Central America were systematically compiled to constrain our new 3D plate tectonic synthesis since the Middle Jurassic (165 Ma). This new model strongly indicates a possible correlation between the SSM and SMM, which where probably formed in the Pacific frontal subduction zone during Late Jurassic-Early Cretaceous. In contrast, the NMM seems to be the result of a regional back-arc closure during the Late Cretaceous. In summary, the present distribution of Central American HP/LT belts must be the result of a protracted and complicated structural evolution linked to major left-lateral displacement along the North American- Caribbean plate boundary.