Comment on “Sediment provenance and depositional systems during Paleozoic tectonic and climatic transitions in the eastern Precordillera of Argentina” by Regier et al. 2025, Volume 139, Pages 179–203

Abstract

Regier et al. (2025) published a paper integrating facies analyses with detrital and igneous zircon U-Pb geochronology data for the eastern Precordillera (Argentina). Based on these data, the paper proposes a geodynamic model for the Late Cambrian to Middle Carboniferous period. While the detrital and igneous zircon U-Pb geochronology data are robust, the proposed geodynamic interpretation for the Devonian-Carboniferous period is inconsistent with the data, as discussed below. Additionally, some references to our work, Dahlquist et al. (2021), are incorrect (pages 194, 199, and 200). For instance, Dahlquist et al. (2021) did not include the presence of the Chilenia terrane in their geodynamic model, contrary to what is stated in Regier et al. (2025, page 200).As previously reported by Dahlquist et al. (2018; 2021, 2022, and references therein), there is no evidence of a Middle–Late Devonian magmatic arc between 28◦ and 33◦S, and the detrital zircon U-Pb geochronology data from the Carboniferous Jejenes Formation (Precordillera) presented by Regier et al. (2025) align with these prior studies, as detailed below.Samples collected from the Carboniferous Jejenes Formation (Precordillera of Argentina, between ca. 29◦ and 33◦S) yielded 429 individual zircon U-Pb ages, with only six Devonian ages recorded,representing just 1.4 % of the total. Similarly, the absence (or very scarce presence) of Devonian detrital zircon U-Pb ages in the Carboniferous accretionary subduction complex of Chile (see Dahlquist et al., 2018; 2021) is consistent with the zircon U-Pb geochronological data reportedby Regier et al. (2025) in the Jejenes Formation, and supports the absence of a Devonian arc in the outboard region between 28◦ and 33◦S, as indicated by Dahlquist et al. (2021).Moreover, Devonian-age granitic rock outcrops are absent in the Frontal Cordillera between 28◦ and 33◦S and only outcrops further south at ca. 34◦S (Dahlquist et al., 2021, 2022). Instead, between 28◦ and 33◦S, Devonian magmatism developed in the foreland region (presentday Sierras de Córdoba and San Luis), as demonstrated by Dahlquist et al. (2018; 2021).Given this geological framework, the few zircon grains with Devonian ages (1.4 %) likely originated from either Devonian foreland magmatism or the Devonian arc located south of 34◦S. If a magmatic arc had been present in the outboard region, a significantly higher proportionof Devonian detrital zircon U-Pb ages would be expected in the Carboniferous sedimentary record.Consequently, the geodynamic model postulated by Regier et al. (2025, Fig. 19) is unreliable with the geochronological data described above, and leads to misleading interpretations. Based on the described data, any geodynamic model for the referred region between 28◦ and 33◦S must account for the absence of Devonian arc magmatism and the presence of Devonian foreland magmatism. Subsequently, Carboniferous arc and retro-arc magmatism developed. In Argentina, outcrops ofthe Carboniferous magmatic arc occur north of the area studied by Regier et al. (2025) (Dahlquist et al., 2018; 2021), while in Chile, the Carboniferous magmatic arc, which is younger than the one inArgentina, is recognized between approximately 27◦ and 35◦S (see Fig. 11 in Dahlquist et al., 2021, and Moreno et al., 2020).