Devonian to Early Carboniferous Retreating—Advancing Subduction Switch in the Northwestern Patagonia Accretionary Orogen: U‐Pb and Lu‐Hf Isotopic Insights

MARCOS, PAULO; RENDA, EMILIANO M.; GONZÁLEZ, PABLO D.; ORIOLO, SEBASTIÁN; SCIVETTI, NICOLÁS; BENEDINI, LEONARDO; GERALDES, MAURO; GREGORI, DANIEL; YOYA, MARÍA BELÉN; BAHÍA, MARCOS

TECTONICS

AMER GEOPHYSICAL UNION

Año: 2023 vol. 42

0278-7407

In this contribution, we present new early middle Devonian igneous and metaigneous units witha major juvenile magmatic source input in the North Patagonian Massif, which were discovered through U-Pband Lu-Hf zircon analyses. Afterward, we assessed their tectonic implications for northwestern Patagonia andthen for southern South America, combining our results with available database information consistingof igneous crystallization ages and isotopic data of the Devonian to early Carboniferous magmatic units,tectonic-metamorphic analyses, and thermochronologic record. This study allows for distinguishing retreatingand advancing subduction switching in northwestern Patagonia (38°30′ to 44°S) and a contrasting coetaneousevolution for basement outcrops exposed further north (27°30′ and 37°30′S). The early middle Devonian(400–380 Ma) northwestern Patagonian magmatism is characterized by widespread magmatism and positiveεHf–εNd linked to forearc and backarc magmatism that evolved within a retreating subduction stage. A tectonicswitching toward advancing orogeny stage began in the late Devonian, evidenced by a lull in magmatic activitywith a negative εHf–εNd trend, possibly contemporaneous with the first tectonic-metamorphic event in westernPatagonia. An early Carboniferous magmatic gap, followed by the subsequent development of the main foliationin the basement during the Carboniferous-Permian period, denotes the acme of this contractional stage. Incontrast, the Devonian period in the northern segment is characterized by mostly negative εHf–εNd values,reverse shear zone activity in the foreland, and an inboard magmatism migration, evidencing a compressivetectonic setting that changed to an extensional configuration in the early Carboniferous with widespread arcmagmatism development.