Evidence for Caribbean Plate Subduction Beneath the Isthmus of Panama and Implications for Subduction Initiation and the Closure of the Central American Isthmus During the Miocene

The evolution of the Isthmus of Panama during the Miocene resulted in climatic shifts leading to global cooling, reorganization of ocean currents, and regional mass extinctions. The causes of this change in ocean circulation between ∼15 and 5 Ma have been debated, with various tectonic scenarios being proposed as explanations for this event. However, few geophysical imaging investigations have been carried out beneath Panama to probe the tectonic structure of this region. Here we investigate the crust and upper mantle of the Isthmus of Panama, directly beneath the Panama Canal, using seismic receiver function analysis. We focus on back‐azimuthal harmonic regression to isolate directionally dependent signals. We report evidence for clearly defined southernly dipping anisotropic layers at depths between ∼38 and 49 km, coincident with relocated seismicity beneath the Panama landmass. Our tectonic interpretation is informed by a synthetic modeling exercise incorporating a Bayesian inversion framework to investigate the harmonic regression terms. We interpret our results as evidence for Caribbean Plate subduction beneath the Isthmus of Panama. Considering our results, the depths of relocated seismicity, and present‐day plate motion, we estimate that Caribbean Plate subduction initiated ∼14–10 Ma, broadly coincident with changes in deep ocean circulation through what is today the Panama landmass. We propose that incipient subduction caused progressive uplift of the overriding plate, leading to the cessation of deepwater flow ∼7.5 Ma and of shallow water flow ∼5 Ma, and culminating in the formation of the isthmus of Panama and the Great American Biotic Interchange by ∼2.7 Ma.