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Abstract:
In Northwestern South America (NWSA) geodetic observations point to a consistent northeastward displacement of blocks, while the geological record shows a predominant shortening in NW-SE direction. Such clear evidence of strain partitioning has been extensively studied in the context of two convergent plates, but not in complex tectonic area involving several plates or tectonic blocks, such as in the northern Andes, where NWSA interacts with the Caribbean and Farallon/Nazca plates and the Panama-Choco Arc. We propose a new deforming plate reconstruction for the region that integrates crustal deformation along the NWSA margin into a recent kinematic plate motion model in the Cenozoic. This approach enables a qualitative analysis of strain partitioning over time. Our results indicate that deformation was neither spatially homogeneous nor did it occur continuously. The main drivers of the distribution of deformation were variations of convergence obliquity, heterogeneous lithospheric strength, geometry of the subducting slabs and the transition from subduction to collisional tectonics of the Panama-Choco Arc against NWSA. Our deforming plate model reproduces a strain-rate evolution consistent with the different episodes of deformation reported in the region. Beyond accounting for cumulative deformation, the present-day reconstructed velocity and strain vectors show strong agreement with modern geodetic data and earthquake focal mechanism solutions. Moreover, by integrating our reconstruction with paleoenvironmental interpretations, we propose a paleogeographic evolution of the region for the Cenozoic that closely aligns with the deformation and exhumation history of the northern Andes.
