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

Abstract

The Talamanca Cordillera in the Central America Arc (Costa Rica‐Panama) preserves the record of the geochemical evolution from an intraoceanic arc to a juvenile continental arc in an active subduction zone, making it a testbed to explore processes that resulted in juvenile continental crust formation and explore potential mechanisms of early continental crust generation. Here we present a comprehensive set of geochronological, geochemical, and petrological data from the Talamanca Cordillera that tracks the key turning point (12–8 Ma) from the evolution of an oceanic arc depleted in incompatible elements to a juvenile continent. Most plutonic rocks from this transition and postintrusive rocks share striking similarities with average upper continental crust and Archean tonalite, trondhjemite, and granodiorite. We complement these data with seismic studies across the arc. Seismic velocities within the Caribbean Plate (basement of the arc) show a relatively uniform lateral structure consistent with a thick mafic large igneous province. Comparisons of seismic velocity profiles in the middle and lower crust beneath the active arc and remnant Miocene arc suggest a transition toward more felsic compositions as the volcanic center migrated toward the location of the modern arc. Seismic velocities along the modern arc in Costa Rica compared with other active arcs and average continental crust suggest an intermediate composition beneath the active arc in Costa Rica closer to average crust. Our geochemical modeling and radiogenic isotopes systematics suggest that input components from melting of the subducting Galapagos hotspot tracks are required for this compositional change.

A Single Dras‐Kohistan‐Ladakh Arc Revealed by Volcaniclastic Records

“…In other words, the trace element geochemistry of 160-80 Ma igneous and sedimentary rocks of the Dras arc is indistinguishable from that of the 160-80 Ma igneous rocks of the Kohistan-Ladakh arc. The post-80 Ma change to more enriched trace element compositions in the Kohistan-Ladakh arc (e.g., Jagoutz et al, 2019) is a feature commonly described in other intraoceanic arcs shifting from primitive to mature stages (e.g., Costa Rica, Gazel et al, 2019;Aleutians, Kay et al, 2019;Izu Bonin, Saito & Tani, 2017), although the causes of such a compositional shift may differ from one arc setting to the other.…”

A Recent Tear in Subducting Plate Explains Seismicity and Upper Mantle Structure of Southern Costa Rica

“…Near‐orthogonal subduction of typical oceanic lithosphere from the East Pacific Rise occurs in the north, with subduction signatures of upper‐plate volcanism, a clearly defined Wadati‐Benioff zone, and a deep offshore trench (Lücke & Arroyo, 2015; Protti et al., 1995). To the south where the Cocos Ridge and PFZ converge with the Costa Rican land mass, the nature of subduction and its typical geochemical signatures change (e.g., Gazel et al., 2019). Arc‐typical volcanism is absent and seismicity is reduced, with no magnitude 4.0+ earthquakes deeper than 70 km observed from south Costa Rica to Colombia (Figure 1).…”

“…Presently, three primary hypotheses have been published to explain the change in the southern Central American subduction zone, all focusing on the geometry and history of the Cocos plate beneath southern Costa Rica. These hypotheses range from a steeply dipping aseismic slab (Dzierma et al, 2011;Lücke & Arroyo, 2015), to a nearly or completely flat slab (Fisher et al, 2004;Gardner et al, 1992;Morell et al, 2016), to a slab window being present (Gazel et al, 2011(Gazel et al, , 2019Johnston & Thorkelson, 1997). Each model predicts possible impedance structures and can be directly tested.…”

Formation of Continental Crust by Diapiric Melting of Recycled Crustal Materials in the Mantle Wedge

“…However, this raises a well‐known paradox of CC formation that mantle‐derived melts are generally basaltic and differ from CC, which has an overall andesitic‐dacitic composition (Figure 1a; Rudnick & Gao, 2014). Resolving this discrepancy has proven to be a challenge, and three models are generally invoked: (a) delamination of mafic/ultramafic rock of lower crust into the mantle (Figures 1b−1c; Herzberg et al., 1983; Jagoutz & Kelemen, 2015; Lee & Anderson, 2015; Ringwood & Green, 1966); (b) relamination of subducted felsic rock to the base of the arc (Figures 1d−1e; Hacker et al., 2011, 2015; Hess, 1962; Kelemen & Behn, 2016); and (c) partial melting of basaltic oceanic crust (Gazel et al., 2015, 2019; Green & Ringwood, 1968) or eroded arc crust (Gómez‐Tuena, Mori, & Straub, 2018; Straub et al., 2015) in the mantle. All three processes may occur, but whether any mechanism dominates CC formation is unclear.…”