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

Author:

Marcos Paulo12ORCID,Renda Emiliano M.12,González Pablo D.3ORCID,Oriolo Sebastián4ORCID,Scivetti Nicolás5ORCID,Benedini Leonardo67ORCID,Geraldes Mauro8,Gregori Daniel67,Yoya María Belén4,Bahía Marcos69

Affiliation:

1. Universidad Nacional de Río Negro Instituto de Investigación en Paleobiología y Geología Río Negro Argentina

2. IIPG UNRN CONICET General Roca Argentina

3. CONICET‐SEGEMAR Regional Sur General Roca Argentina

4. CONICET‐Universidad de Buenos Aires Instituto de Geociencias Básicas Aplicadas y Ambientales de Buenos Aires (IGEBA) Buenos Aires Argentina

5. Instituto Patagónico de Geología y Paleontología –IPGP‐ (CENPAT‐CONICET) Puerto Madryn Argentina

6. Instituto Geológico del Sur (INGEOSUR) Universidad Nacional del Sur (UNS)‐CONICET Bahía Blanca Argentina

7. Departamento de Geología Universidad Nacional del Sur (UNS) Bahía Blanca Argentina

8. Departamento de Geología Regional Facultad de Geología Universidad Estatal de Río de Janeiro Rio do Janeiro Brazil

9. Departamento de Física Universidad Nacional del Sur (UNS) Bahía Blanca Argentina

Abstract

AbstractIn this contribution, we present new early middle Devonian igneous and metaigneous units with a major juvenile magmatic source input in the North Patagonian Massif, which were discovered through U‐Pb and Lu‐Hf zircon analyses. Afterward, we assessed their tectonic implications for northwestern Patagonia and then for southern South America, combining our results with available database information consisting of 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 retreating and advancing subduction switching in northwestern Patagonia (38°30′ to 44°S) and a contrasting coetaneous evolution 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 positive εHf–εNd linked to forearc and backarc magmatism that evolved within a retreating subduction stage. A tectonic switching toward advancing orogeny stage began in the late Devonian, evidenced by a lull in magmatic activity with a negative εHf–εNd trend, possibly contemporaneous with the first tectonic‐metamorphic event in western Patagonia. An early Carboniferous magmatic gap, followed by the subsequent development of the main foliation in the basement during the Carboniferous‐Permian period, denotes the acme of this contractional stage. In contrast, 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 compressive tectonic setting that changed to an extensional configuration in the early Carboniferous with widespread arc magmatism development.

Publisher

American Geophysical Union (AGU)

Subject

Geochemistry and Petrology,Geophysics

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