Extending the Pampean orogen in western Argentina: New evidence of Cambrian magmatism and metamorphism within the Ordovician Famatinian belt revealed by new SHRIMP U–Pb ages

Abstract

New SHRIMP U–Pb zircon and monazite ages from the Sierra de Fiambalá (Sierras Pampeanas, NW Argentina) record coeval granitoid peraluminous magmatism and high-grade metamorphism at ca. 525 Ma (Lower Cambrian) that resulted from the collisional Pampean orogeny. The Sierra de Fiambalá, however, is well within the Ordovician accretionary Famatinian orogenic belt and west of what is commonly regarded as the Pampean orogenic belt in the Eastern Sierras Pampeanas (ESP). It is thus an inlier that can be correlated chronologically and stratigraphically with the Pampean high-grade metamorphic domain in the Sierras de Córdoba (ESP). Moreover, in the Fiambalá inlier, Ediacaran to early Cambrian meta-sedimentary rocks of the Ancaján Series, of an alleged Laurentian source, predominate relative to the Puncoviscana Formation of Gondwanan provenance. Two tectonic interpretations are proposed for the origin of the Fiambalá inlier: (1) it is a Pampean basement thrusted westward during the Famatinian orogeny or (2) it was rifted away from the main Pampean orogenic belt sometime between the end of the Pampean orogeny and the start of the Famatinian orogeny and later reworked by the latter in coincidence with the proposal by Weinberg et al. (2018). The evidence given here confirms that rocks of the Pampean orogen extend far westward of the main Pampean belt (≥300 km).