Magmatic evolution of Panama Canal volcanic rocks: A record of arc processes and tectonic change

Abstract

Volcanic rocks along the Panama Canal present a world-class opportunity to examine the relationship between arc magmatism, tectonic forcing, wet and dry magmas, and volcanic structures. Major and trace element geochemistry of Canal volcanic rocks indicate a significant petrologic transition at 21–25 Ma. Oligocene Bas Obispo Fm. rocks have large negative Nb-Ta anomalies, low HREE, fluid mobile element enrichments, a THI of 0.88, and a H2Ocalc of >3 wt. %. In contrast, the Miocene Pedro Miguel and Late Basalt Fm. exhibit reduced Nb-Ta anomalies, flattened REE curves, depleted fluid mobile elements, a THI of 1.45, a H2Ocalc of <1 wt. %, and plot in mid-ocean ridge/back-arc basin fields. Geochemical modeling of Miocene rocks indicates 0.5–0.1 kbar crystallization depths of hot (1100–1190°C) magmas in which most compositional diversity can be explained by fractional crystallization (F = 0.5). However, the most silicic lavas (Las Cascadas Fm.) require an additional mechanism, and assimilation-fractional-crystallization can reproduce observed compositions at reasonable melt fractions. The Canal volcanic rocks, therefore, change from hydrous basaltic pyroclastic deposits typical of mantle-wedge-derived magmas, to hot, dry bi-modal magmatism at the Oligocene-Miocene boundary. We suggest the primary reason for the change is onset of arc perpendicular extension localized to central Panama. High-resolution mapping along the Panama Canal has revealed a sequence of inward dipping maar-diatreme pyroclastic pipes, large basaltic sills, and bedded silicic ignimbrites and tuff deposits. These volcanic bodies intrude into the sedimentary Canal Basin and are cut by normal and subsequently strike-slip faults. Such pyroclastic pipes and basaltic sills are most common in extensional arc and large igneous province environments. Overall, the change in volcanic edifice form and geochemistry are related to onset of arc perpendicular extension, and are consistent with the idea that Panama arc crust fractured during collision with South America forming the observed Canal extensional zone.

Transition From Collisional to Subduction‐Related Regimes: An Example From Neogene Panama‐Nazca‐South America Interactions

“…Increased tectonic instability during middle Miocene times has been also documented throughout the northwestern Andes and southern Central America from the analysis of the magmatic and deformational record of the region and has been attributed to the collision of the Panama Arc with northwestern South America (Farris et al, , ; Montes, Bayona, et al, ; Ramírez et al, ; Villagómez & Spikings, ) (Farris et al, , ; Montes, Bayona, et al, ; Ramírez et al, ; Spikings et al, ; Villagómez & Spikings, ). Exhumation, increased accumulation rates, and switch from mudstone facies to fluvial conglomeratic facies also document increased instability inboard the continent, in the inter‐Andean Magdalena Valley and Eastern Cordillera (Reyes‐Harker et al, , and references therein).…”

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

“…Our survey was designed to provide new, systematic constraints on volcanic processes recorded in new exposures of the Gaillard Cut and Pacific locks area created during widening of the Canal since 2008, as well as their possible lateral equivalents along nearby rivers and roadcuts in Central Panama. Our study partly built upon previous results by Farris et al (2017) and was carried out in collaboration with the Panama Canal Authority that has done detailed lithological and structural mapping of the Gaillard Cut and Pacific locks area during recent expansion of the Canal. Our study additionally benefited from access to a large collection of cores collected during the expansion.…”

“…The study of the volcanic and magmatic evolution of Central Panama between the Oligocene and Miocene has recently focused on volcanogenic units of the Canal area (Farris et al, 2011(Farris et al, , 2017Rooney et al, 2011) that postdate an uplifted Maastrichtian to Eocene volcanic basement which is part of the nearby Chagres-Bayano Arc (Montes et al, 2012b;Wegner et al, 2011;Wörner et al, 2005) (Fig. 1).…”

“…Rooney et al (2011) document amphibole-bearing andesites (Cerro Patacon unit), which record formation of water-saturated magmas in the Canal area during the Oligocene. Farris et al (2011Farris et al ( , 2017 recognised Miocene tholeiitic series along the Gaillard Cut of the Panama Canal, which they propose reflect an atypical phase of anhydrous magmatism during a rifting event ca. 23 Ma.…”

Synthesis of geological and comparative phylogeographic data point to climate, not mountain uplift, as driver of divergence across the Eastern Andean Cordillera

“…Political boundaries and the outline of Maracaibo Lake for reference. Most coarse-grained deposits at this time are sandy, from mostly fluvial and near-shore environments, and mark the segmentation of basins by rising mountain belts (Anderson et al, 2015; Barat et al, 2014; Borrero et al, 2012; Erikson et al, 2012; Farris et al, 2017; Gomez et al, 2005; Grosse, 1926; Guerrero, 1997; Hoorn et al, 2010; Leon et al, 2018; Montes et al, 2010; Moreno et al, 2015; Parnaud et al, 1995; Quiroz et al, 2010). Only two possible lowland passages are allowed at this time by these lithostratigraphic constraints and fish faunas: The Putumayo (Lundberg and Chernoff, 1992) to the South, and the Táchira corridor to the North.…”