Primitive Magmas in the Early Central American Volcanic Arc System Generated by Plume-Induced Subduction Initiation

Abstract

Primitive magmatic rocks with Mg# ≥60 have been identified in the literature from the Sona-Azuero, Golfito and Chagres-Bayano forearc segments of southern Costa Rica and Panama of the early (75-39 Ma) Central American Volcanic Arc system (CAVAS). Primitive CAVAS basalts are remarkably similar in terms of major and many trace elements to primitive MORB and primitive basalts of the Mariana Arc and share affinities with global intra-oceanic arc tholeiitic and calc-alkaline basalts. Significant differences however, are apparent between primitive lavas of Chagres-Bayano relative to those of Sona-Azuero and Golfito. Primitive Chagres-Bayano lavas record much higher degrees of partial melting and higher amounts of shallow and deep subduction additions (e.g., higher Ba/Th, Th/Nb) than those of the older Sona-Azuero and Golfito arc segments which reflects the early petrologic and tectonic evolution of the CAVAS which is similar to other forearc systems. As shown in previous studies, early CAVAS lavas are exceptionally similar in radiogenic isotopic composition to those of the Caribbean Large Igneous Province (CLIP) oceanic plateau at 90 Ma, the approximate timing of onset of the volumetrically dominant phase of CLIP magmatism. Moreover, calculated potential temperatures of 1,633 ± 47 • C for two Sona-Azuero primitive basalts suggests an anomalously hot mantle source at subduction initiation (SI). These insights are consistent with SI models which require a plume-induced SI scenario and an elevated sub-arc thermal anomaly upon inception of the CAVAS. It is postulated that, in addition to providing an anomalously high temperature regime in the sub-arc mantle at inception of the CAVAS, extrusion of the CLIP also resulted in lithospheric weakening and extension which allowed for production and rapid ascent of a high percentage of primitive magmas.

Plume‐Induced Sinking of Intracontinental Lithospheric Mantle: An Overlooked Mechanism of Subduction Initiation?

“…Natural observations of this process, however, are notoriously rare. Despite numerous intra‐oceanic “hot‐spots” (Courtillot et al., 2003), only one of them has triggered subduction around the Caribbean plate in the Late Cretaceous (Whattam, 2018; Whattam & Stern, 2015), whereas in all other cases no proven hot spot‐related ocean‐ocean subduction has been detected so far. One of the most prominent “negative” examples is the North Atlantic Igneous Province (Saunders et al., 1997) associated with the Iceland plume that 1) produces melt during most of the past 60 Myr (e.g., Kerr, 2003), thus contributing to melt‐induced magmatic weakening of the overlying plate, which is typically the most important condition for plume‐induced subduction (Ueda et al., 2008, Gerya et al., 2015; Baes et al., 2016, 2020a, 2020b); 2) has presumably triggered the opening of the North Atlantic Ocean at ∼60 Ma (Beniest et al., 2017b) and caused the active spreading axis to jump from the Aegir ridge to the Kolbeinsey ridge at ∼30–35 Ma (Koptev et al., 2017), thus attesting a sufficiently high buoyancy of the plume to overcome the strength of not only oceanic but even continental lithosphere; 3) channeled along the thin‐lithosphere corridors underneath continental lithosphere and the mid‐oceanic ridges (Steinberger et al., 2019); 4) presently extends not only along the mid‐oceanic ridge but also in perpendicular directions (see seismic tomography by Rickers et al., 2013 and laboratory and numerical experiments by Schoonman et al., 2017 and Koptev et al., 2017, respectively), thus impinging oceanic lithosphere of ages older than 20 Ma as required for the formation of stable subduction zones in numerical experiments (Baes et al., 2016; Lu et al., 2015).…”

The Record of the Transition From an Oceanic Arc to a Young Continent in the Talamanca Cordillera

“…The edges of oceanic plateaus have been proposed as the places for the onset of subduction and gradual production of juvenile continental material (Gerya et al, 2015;Stein & Goldstein, 1996;Whattam, 2018). This is an important model to consider because the arc in southern Central America developed in the westernmost edge of the Caribbean Plateau (e.g., Denyer & Gazel, 2009;Hauff et al, 2000).…”

“…Intraoceanic arcs provide modern analogues for the "subduction model" of new continental crust, in this case both subducting and overriding plates have an oceanic origin (Rudnick & Gao, 2003). (b) Volcanic Arc evolution record in Costa Rica: Note that the northwestern section of the arc exposes extrusive volcanic units since the Mid-Miocene-Pliocene, the southeastern section (the Talamanca Cordillera) preserves mostly Miocene intrusive rocks (Alvarado & Gans, 2012;Denyer & Alvarado, 2007;Gazel et al, 2009;Whattam, 2018). includes erupted material that is geochemically similar to Archean TTGs. Therefore, in order to elucidate the processes that produce juvenile continental crust in subduction systems, focus must be directed toward arcs where the volcanic output resembles juvenile continental crust produced in the Archean.…”

“…Therefore, in order to elucidate the processes that produce juvenile continental crust in subduction systems, focus must be directed toward arcs where the volcanic output resembles juvenile continental crust produced in the Archean. This arc crust must represent an average upper continental crust composition that also (Alvarado & Gans, 2012;Denyer & Alvarado, 2007;Gazel et al, 2009;Whattam, 2018). includes erupted material that is geochemically similar to Archean TTGs. On the basis of the correlation between average V P and a continental index used to compare the chemical composition of magmas produced to global continental crust estimates (Gazel et al, 2015), one of the best locations to study the production of juvenile continental crust is along the Central American Land Bridge (Costa Rica and Panama, Figure 1).…”

Evolution of the Northern Part of the Lesser Antilles Arc—Geochemical Constraints From St. Barthélemy Island Lavas

“… (a) Map of the greater Caribbean region showing the distribution of the Caribbean Plate (modified from Whattam, 2018). LAA System : Lesser Antilles Arc System; GAC System : Great Arc of the Caribbean System; Caribbean LIP : Caribbean Large Igneous Province.…”