Magmatic consequences of the transition from orthogonal to oblique subduction in Panama

Abstract

The closure of the Central American Seaway is linked with tectonic and magmatic processes that have controlled the evolution of the Isthmus of Panama. We focus on the terminal stages of arc activity in the Central Panama region, and present new geochemical data from ∼9 Ma explosive silicic volcanism preserved in three syngenetic tuff beds from the Gatun. The magmatic evolution of the Gatun Formation is controlled by a series of magma mushes where pyroxene is the dominant early forming mafic mineral, with amphibole appearing only relatively late in the fractionation sequence. Our data show Gatun lavas exhibit a strong subduction signature, consistent with plate reconstruction models showing arc‐normal subduction from Costa Rica to Panama pre‐8.5 Ma. However, large ion lithophile elements are depleted in the Gatun Formation in comparison to other regional suites, indicative of a lower flux of subduction fluid to the Gatun Formation mantle source, which is explained by a shift toward magma generation by decompression following the collision of the arc with South America. Oblique subduction commencing ∼8.5 Ma resulted in the shutdown of normal arc activity throughout Panama. We interpret subsequent regional Quaternary adakitic volcanism as a response to this oblique subduction. The now more refractory mantle wedge required greater fluid flux in order to melt. The resultant volatile‐rich melts were more prone to deep fractionation of amphibole and garnet cumulates forming adakites. Deep fractionation was potentially enhanced by changing stress regimes on the upper plate caused by oblique subduction.

Plio‐Quaternary Outer Forearc Deformation and Mass Balance of the Southern Costa Rica Convergent Margin

“…Late Miocene extinction of calc‐alkaline volcanism within this range had been associated with uplift of the Talamanca due to Cocos Ridge subduction (Abratis & Wörner, ; de Boer et al, ). However, similar‐aged extinction of adjacent arc segments in Panama (Wegner et al, ) suggest that late Miocene shut‐off of calc‐alkaline active volcanism in the Talamanca was not linked to Cocos Ridge subduction and was rather related to a late Miocene plate tectonic reconfiguration (Morell, ; Morell et al, ; Rooney et al, ). The increase in range width, high elevations, and deeply incised river reaches draining the Talamanca suggest ongoing and recent rock uplift within the past few million years (Morell et al, ).…”

Late Jurassic to Early Cretaceous plutonism in the Colombian Andes: A record of long-term arc maturity

“…As oblique convergence continued and the subducted hybrid mélange was melted, losing the sedimentary input and increasing the basaltic and serpentinite signature, arc magmatism became isotopically more juvenile and refractory. As convergence became more oblique, the formation of new mélanges and fluid flow in the mantle wedge were also reduced (Hoernle et al, 2008;Malatesta et al, 2013;Rooney et al, 2015), contributing to the reduction in the magmatic products seen in the Late Jurassic to Early Cretaceous arc.…”

Melting the lithosphere: Metasomes as a source for mantle-derived magmas

“…The resulting powders were fused with lithium tetraborate at a ratio of 1:3 following procedures 123 detailed elsewhere (Rooney et al, 2015). The resulting disks were analyzed for major elements 124 by a Brucker S4 Pioneer XRF at Michigan State University.…”