Early Paleozoic accretionary orogens along the Western Gondwana margin

ORIOLO, SEBASTIÁN; SCHULZ, BERNHARD; GEUNA, SILVANA; GONZÁLEZ, PABLO D.; OTAMENDI, JUAN E.; SLÁMA, JI?Í; DRUGUET, ELENA; SIEGESMUND, SIEGFRIED

Geoscience Frontiers

Elsevier

Año: 2020

1674-9871

EarlyPaleozoic accretionary orogens dominated the Western Gondwana margin and werecharacterized by nearly continuous subduction associated with crustal extensionand back-arc basin development. The southwestern margin is represented byFamatinian and Pampean basement realms exposed in South America, both relatedto the protracted Paleozoic evolution of the Terra Australis Orogen, whereasthe northwestern margin is mainly recorded in Cadomian domains of Europe andadjacent regions. However, no clear relationships between these regions were sofar established. Based on a compilation and reevaluation of geological,paleomagnetic, petrological, geochronological and isotopic evidence, thiscontribution focuses on large-scale tectonic and geodynamic processes occurringin Western Gondwana accretionary orogens, aiming at disentangling their commonEarly Paleozoic evolution. Results show that accretionary orogens weredominated by high-temperature/low-pressure metamorphism and relatively highgeothermal gradients, resulting from the development of transtensionalextended/hyperextended margins. In this sense, retreating-mode accretionaryorogens characterized the Early Paleozoic Gondwana margin, though short-livedpulses of compression/transpression also occurred. The existence of retreatingsubduction zones favoured mantle-derived magmatic intrusion and mixing withrelatively young (meta)sedimentary sources in a thin continental crust. Crustalreworking of previous forearc sequences due to trenchward arc migration thustook place through assimilation and anatexis in the arc/back-arc regions.Therefore, retreating-mode accretionary orogens were the locus of EarlyPaleozoic crustal growth in Western Gondwana, intimately associated with majorflare-up events, such as those related to the Cadomian and Famatinian arcs.Slab roll back, probably resulting from decreasing convergence rates and platevelocities after Gondwana assembly, was a key factor for large-scale geodynamicprocesses. Coupled with oblique subduction and crustal-scale dextraldeformation, slab roll back might trigger toroidal mantle flow, thus accountingfor widespread marginal back-arc extension/transtension and a large-scalecounter-clockwise rotation of Gondwana mainland. Finally, similarities in theEarly Paleozoic record may also suggest a comparable evolution for EasternGondwana marginal segments.