THE FORMATION OF THE MIDDLE AMERICA AND THE PACIFIC OCEAN

A new synthesis of the plate tectonic evolution of the Middle America region (Southern California to Ecuador) and the Pacific Ocean since the Pangea break-up (230 Ma, Late Triassic) has been developed. The model is based on data derived from different geological and geodynamic constraints. In addition to detailed analysis of different continental blocks and accretionary complexes, the distribution, composition, and age of high-pressure-low-temperature (HP-LT) rocks, magmatic activity, sedimentary patterns, metamorphism, structural geology, paleomagnetic data, and geophysics have been systematically compiled and evaluated.

Kinematic reconstructions, performed using ArcGis®, enabled application and quantification of rotational motions and spreading/subduction rates to the numerous plates and tectonic blocks involved in the evolution of the study area. Boundary conditions are provided by the relative motions of the plates with respect to a fixed Baltica. Plate tectonic concepts were applied throughout the process, with plate boundaries being built and transformed in space and time. Plate velocities were calculated in all reconstructions and never exceed of 20 cm/y.

This new model allows a more comprehensive analysis of the tectonic development of the study area. In particular, the relationship and timing between (i) rift propagation and back-arc opening during the Pangea break-up, (ii) intra-oceanic collision, and subduction initiation in the paleo-North America active margin, (iii) island arc rifting, back-arc spreading, and inception of the intra-oceanic arcs in the paleo-Pacific ocean, (iv) island arc-active margin collision, back-arc inversion, active margin-passive margin collision, and translation of fragments of larger terranes along the Middle America margin, as well as (v) subduction zone evolution and exhumation of HP-LT rocks.