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 16Ma, with a progressive change from calcalkaline 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. 16Ma. 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.

Submarine volcanic activity and giant amygdale formation along the Panama island arc as a precursor to 6000-year-old agate exploitation on Pedro González Island

“…This is consistent with the hypothesis that a decrease of hydrous slab component accompanied magmatic cessation regionally (Farris et al 2011;Buchs et al 2019a). Therefore, the unusual composition of Pedro González igneous suite suggests emplacement during or shortly before magmatic cessation, which is constrained to c. 16 Ma based on previous data from the Canal area (Buchs et al 2019a). This age of emplacement is also broadly consistent with previous geochronological constraints from igneous rocks in the Pearl Island archipelago (Lissinna, 2005), although caution is required in this comparison considering observed geochemical differences with Pedro González Island (Fig.…”

“…8), the analysed igneous rocks have the most extreme tholeiitic character found to date in Panama. This is consistent with the hypothesis that a decrease of hydrous slab component accompanied magmatic cessation regionally (Farris et al 2011;Buchs et al 2019a). Therefore, the unusual composition of Pedro González igneous suite suggests emplacement during or shortly before magmatic cessation, which is constrained to c. 16 Ma based on previous data from the Canal area (Buchs et al 2019a).…”

“…9d). High TiO 2 contents have only previously been observed in tholeiitic series of the Panama Canal area (c. 21 to 16 Ma) that are associated with magmatic cessation in central Panama (Buchs et al 2019a).…”

“…2), we have not yet found exposures of pre-Oligocene igneous basement overlain by shallow-marine limestones and conglomerates in the Pearl Islands. In addition, new geochemical results indicate that igneous rocks on Pedro González Island are compositionally similar to the post-Eocene volcanic arc, and most particularly to the early Miocene tholeiitic sequences of the Canal area that are associated with magmatic cessation in central Panama c. 16 Ma ago (Buchs et al 2019a;Figs 8, 9). As indicated by the AFM diagram and FeO*/MgO and CaO/Al 2 O 3 ratios (Fig.…”

“…However, younger volcanism has not been documented yet in eastern Panama. Magmatic cessation occurred c. 16 Ma ago in the Canal area, which could also correspond to the end of volcanism in eastern Panama (Buchs et al 2019a). As further discussed below, only two samples of igneous rocks have been analysed and dated in the Pearl Island archipelago (Lissinna, 2005), which suggest the occurrence of early Miocene (c. 22 to 18 Ma) arc volcanism in the studied area.…”