Geochronology and geochemistry of Devonian magmatism in the Frontal cordillera (Argentina): geodynamic implications for the pre-Andean SW Gondwana margin

ABSTRACT

Whereas north of 33°S Devonian calcalkaline magmatism is notably absent, a Devonian arc is well developed to the south of 33°S. The Carrizalito, Pampa de los Avestruces, and Papagayos plutons are located in the Frontal Cordillera between 34° and 35°S. U-Pb zircon SHRIMP and LA-MC-ICP-MS data from the plutons yield Early Devonian ages of 389 ± 3 and 409 ± 3 for Carrizalito, 413 ± 2 Ma for Pampa de los Avestruces, and 346 ± 3, 393 ± 5 and 412 ± 3 Ma for Papagayos. The younger zircon age from the Papagayos pluton suggests that the Devo nian magmatism continued during the Early Carboniferous. Carrizalito and Pampa de los Avestruces plutons display metaluminous to slightly peraluminous granodiorite composition, with SiO₂ ranging from 65.1 to 67.8 wt.% and from 67.9 to 69.7 wt.%, respectively, and define a magnesian calc-alkalic trend. The Papagayos pluton is metaluminous to slightly peraluminous and slightly more evolved in composition (felsic granodiorite to monzogranite), with a SiO₂ content that varies between 68.4 to 70.5 wt.%, defining a magnesian with ferroan enrichment and calc-alkalic to alkali-calcic trend. These geochemical characteristics are similar to those reported for the Carboniferous arc granitoids in the Frontal Cordillera and Western Sierras Pampeanas at 27°–30°S and the archetypical calc-alkaline granitoids of the Peruvian Coastal batholith, indicating an Early Devonian magmatic arc. Rare earth element patterns ([La/Yb]_N = 10–20) with mostly slight to moderate negative Eu anomalies (Eu/Eu* = 0.62–0.80) and geochemical ‘spider-diagrams’ are similar to arc granitoids. Combined whole-rock Nd and Sr isotope data from the largest Carrizalito and Pampa de los Avestruces plutons (εNd_t = −4.3 and −4.6; ⁸⁷Sr/⁸⁶Sr_t = 0.70704 and 0.70762; T_DM = ca. 1.5 Ga) together with in situ U–Pb and Hf isotope data from magmatic zircon (εHf_t ranging from −16.5 to −5.4; T_DM = ca. 1.7 Ga), suggest a common older continental lithosphere source. The presented data indicate tectonic segmentation in the pre-Andean margin controlling the presence or absence of Devonian subduction-related magmatism. This segmentation is best explained by changes in the tectonic plate configuration occurred in a long-lived convergent margin.

KEYWORDS:

• Devonian calc-alkaline magmatism
• Frontal Cordillera
• SW Gondwana margin
• Tectonic segmented subduction
• Geochronological, Geochemical, and isotopic data

Acknowledgments

Financial support for this paper was provided by Argentine public grants PICT 2016 0843 FONCyT, PIP0178 CONICET, Consolidar 2018 SECyT-UNC, PI15G FCEyN-UNLPam, PUE-CICTERRA-CONICET, Spain public grant CGL2016-76439-P, and a stay developed in the Geosciences Institute of the Sao Paulo University supported by the grant FAPESP 2018/06837-3. We are very grateful for the English edition by Bob Pankhurst. Your editorial work is greatly appreciated by us. JAD thanks Kei Sato for his assistance using SHRIMP. This work was largely discussed with Professor A. Willner (four round review), because we have different geodynamic views. We are grateful for the exacting review of our manuscript as well as the valuable suggestions. We are grateful to the Professor D. Gregori for his revision and to the Editor-in-Chief R. Stern for the editorial handling.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the Consejo Nacional de Investigaciones Científicas y Técnicas [PIP0178]; Fondo Nacional de Ciencia Tecnología e Innovación [2016-0843]; Fundação de Amparo à Pesquisa do Estado de São Paulo [2018/06837-3]; Ministerio de Ciencia e Innovación [CGL2016-76439-P]; Universidad Nacional de Córdoba [SECyT Consolidar 2018]; Universidad Nacional de La Pampa [PI15G]