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Geochronological data pertaining to the structural evolution of the Sierra de San Luis provide important insights into the geodynamic history along the southwestern margin of Gondwana. In the Pringles metamorphic complex, metamorphic fabrics (S 1 ) were affected by two folding events (D 2 and D 3 ) related to the Ordovician approach of the Cuyania terrane. Contemporary formations of high-temperature shear zones record a prominent east-side-up displacement. Resumption of compression due to the Achalian collision with the Chilenia terrane was accommodated by the reactivation of the Famatinian high-temperature shear zones in greenschist facies conditions. K–Ar Ms ages point to their activity up to the Early Carboniferous. The post-Pampean structural evolution of the Pringles metamorphic complex is supported by new Sm–Nd and 207 Pb/ 206 Pb data, which agree with previously proposed early Cambrian sedimentation of the psammopelitic precursors. A Sm–Nd mineral isochron, together with published SHRIMP U–Pb zircon ages, bracket the emplacement of mafic and ultramafic intrusions that control the granulite facies metamorphism between 506 and 478 Ma. A late Cambrian emplacement of the crustal-derived Paso del Rey pluton is suggested by a 207 Pb/ 206 Pb zircon age at 491 ± 19 Ma. The syn-D 2 emplacement of these granitoids indicates that the D 1 to D 2 structural evolution predates the generally assumed Middle Ordovician accretion of the Precordillera/Cuyania terrane. K–Ar Hbl, Ms, and Bt ages and some Rb–Sr mica data record the cooling after the Famatinian metamorphic peak. Ms ages from large Ms booklets suggest a common cooling of the basement of the sierra at approximately 445 Ma, whereas normal-sized muscovites from gneissic rocks (K–Ar ages of ∼380 Ma) indicate slow cooling of the Pringles metamorphic complex with respect to the other basement domains. K–Ar Bt ages between 360 and 340 Ma capture cooling below approximately 300 °C of the basement. Differential cooling is interpreted to reflect the Achalian tectonic cycle as an event separate from the Famatinian process.

The Sierra de San Luis constitutes the southernmost tip of the Eastern Sierras Pampeanas. Its Palaeozoic metamorphic basement units define a key location for the understanding of the accretional history along the proto-Andean margin of Gondwana. Although, it is largely accepted that the polyphase accretional history of the Sierras Pampeanas is preluded by the docking of the Pampean Terrane followed by the Famatinian Orogenic Cycle that involves subduction along the margin of Gondwana and the accretion of the Precordillera (Cuyania) Terrane and finally ceased with the collision of the Chilenia terrane, a vast amount of controversial information concerning the timing and mode of collisions as well as the origin of the different involved crustal fragments within the Eastern Sierras Pampeanas is published. In this paper, those different hypothesis are presented and evaluated under the light of new isotopic data of the Sierra de San Luis. Nd-systematics of the metasedimentary sequences of the Sierra de San Luis indicate that the studied sequences were developed on the Pampean Terrane. An Amazonian origin of the Pampean Terrane that was probably detached from the Arequipa Antofalla Craton is proposed. Furthermore, the correlation of two low-grade phyllitic belts (San Luis Formation) with the widespread Puncoviscana Formation is not supported by Sm-Nd data. It is suggested that the sedimentary precursors of the Pringles Metamorphic Complex and the topping phyllites were sourced on the Pampean Orogen and accommodated in a newly formed back arc basin during the early Famatinian. The cooling history of the basement complex is recorded by an extensive amount of K-Ar muscovite and biotite ages. A high variability in muscovite ages is only partly related to different intrusion times of two pegmatoid generations. Post Famatinian to Achalian crustal scale mylonite formation (-359 Ma) and a rotational exhumation of the central basement unit are causal for the observed K-Ar muscovite age pattern in the range from 395 Ma to 447 Ma. Therefore, the decrease in metamorphic degree from west to east is the result of the erosion level of a crustal profile from the mid lower crust to the upper crust. An even higher variability in K-Ar biotite cooling ages covering the range from 315 Ma to 418 Ma is related to the slow cooling after the Famatinian Orogenic Cycle or reheating during the Achalian Orogenic Cycle and consequent variable reset of the isotopic system. However, ages recorded by biotite booklets substantiate the hypothesis of a differential exhumation of the basement of the Sierra de San Luis.