A review of Devonian-Carboniferous magmatism in the central region of Argentina, pre-Andean margin of SW Gondwana

We review a widespread project database for Devonian-Carboniferous magmatism in the Sierras Pampeanas and Frontal Cordillera between 27 degrees and 35 degrees S, including petrological, geochemical, geochronological, and isotope data, with compiled data from the literature and some new results. We distinguish four main magmatic domains: 1) Devonian Arc, 2) Devonian Foreland, 3) Carboniferous Arc, and 4) Carboniferous Retro-Arc. Devonian segmented subduction led to two oceanic slab configurations: 1) flat-slab subduction in the outboard region and resubduction >800 km inland from the trench, including lithosphere delamination of the upper plate and break off of the subducted oceanic slab, along with asthenospheric mantle upwelling (31 degrees-33 degrees 30'S), and 2) normal subduction (34 degrees 35 degrees S). In the first configuration the arc magmatism was absent, but voluminous foreland magmatism was developed, including small-scale high silica adakite. The second geodynamic setting took place during the latest Devonian and Carboniferous when the oceanic slab roll-back occurred. Arc and retro-arc magmatism were developed coetaneously between 27 degrees and 31 degrees S, with northwest migration that could be explained by movement relative to hot asthenospheric mantle. The arc is represented by calc-alkaline granitoids, whereas retro-arc magmatism consisted of (a) metaluminous to weakly peraluminous A-type granites, and (b) strongly peraluminous A-type granites, these latter with sometimes incomplete isotopic homogenization of the parental magma. Devonian-Carboniferous magmatic evolution here is explained by segmented tectonic subduction and a switch-off and switch-on geodynamic model. Magmatic activity was mainly continuous from ca. 390 to 320 Ma, although compositional variations occurred through time and space (foreland, arc, and retro-arc). Major involvement of mantle sources in the genesis of the Carboniferous arc granites at 28 degrees-30 degrees S contrast with a dominant continental signature in the granites of the Devonian arc at 34 degrees-35 degrees S. These differences are explained by two different configurations in the subduction system related to advance (28 degrees-30 degrees S) or retreat (34 degrees-35 degrees S) of the subducted ocean slab. The main conclusion of this work is that the complex interaction of oceanic and continental plates can produce different types of magmatism (or its absence): subduction processes do not consist only of an oceanic plate sinking under a continental plate.

Automated summary

The study reveals the existence of four magmatic domains in the Chilean Sierras Pampeanas and Frontal Cordillera during the Devonian-Carboniferous period, with different geodynamic settings and magma origins. Through detailed analysis of magmatic activity, it uncovers the evolution of plate subduction systems in different regions, as well as the roles of mantle sources and continental characteristics in magma formation.