Volcanic shutdown of the Panama Canal area following breakup of the Farallon plate

Abstract

The Panama Canal area is a significant part of the Panama Isthmus, where prominent volcanic fronts of eastern Central America are interrupted by a topographic low of unclear tectonic and magmatic origin. Determining why no prominent volcanic system occurs along the Canal is essential to understand the formation of the Isthmus in an area believed to have hosted one of the last inter-American straits between the Atlantic and Pacific Oceans. We provide here new geochronological and geochemical constraints from volcanic units of the Panama Canal that belong to the recently-identified Central Panama Volcanic Field. Whole rock and mineralogical geochemical compositions document a secular magmatic change from ca. 25 to 16 Ma, with a progressive change from calc-alkaline to tholeiitic and possibly alkaline/transitional geochemical affinities. The age of the youngest volcanic unit of the Canal is similar to that of the youngest documented arc volcanism in eastern Panama ca. 18 Ma. We propose based on these observations and consistency with regional geological constraints that the Canal volcanism represents a unique example of magmatic cessation along a volcanic arc. This cessation occurred shortly after the breakup of the Farallon plate ca. 23 Ma, suggesting a causal link between volcanic shutdown and transition from orthogonal to oblique subduction along Central and Eastern Panama. We suggest that this tectonic event suppressed hydrous melting in the subduction zone and led to regional magmatic waning in Central and Eastern Panama ca. 16 Ma. The pre-existence of a transisthmian fault system in Central Panama probably facilitated extraction of the last supra-subduction melts during volcanic shutdown. Our results suggest that the end of volcanism, combined with transisthmian faulting, impeded the development of high topography in the Panama Canal area. Without this unusual tectono-magmatic evolution, the occurrence of a late inter-oceanic strait in Central Panama and the construction of the Panama Canal would not have been possible.