Cambro-Ordovician stratigraphic record of two distinctive Famatinian belts fringing SW Gondwana: insights from SHRIMP U-Pb zircon ages and geochemistry from the Sierra de Famatina (NW Argentina)

The Sierra de Famatina of northwestern Argentina contains one of the best Cambro-Ordovician stratigraphic records of the SW Gondwana margin. Two lithotectonic belts (Calalaste-Narv & aacute;ez and Famatina-Valle F & eacute;rtil), separated by master faults, preserve evidence of two former volcano-sedimentary basins (Eastern and Western, respectively). The Calalaste-Narv & aacute;ez Lithotectonic Belt consists of an Ediacaran to early Cambrian basement unconformably overlain by a 490-480 Ma cover of very low-grade volcano-sedimentary and volcanic succession that presumably formed in an extensional tectonic regime. In contrast, the Famatina-Valle F & eacute;rtil Lithotectonic Belt comprises a basement consisting of the late-lower-to-middle Cambrian metasedimentary Achavil and Negro Peinado formations unconformably overlain by meta/sedimentary and metavolcanic rocks ranging in age from the late Cambrian to the Middle Ordovician (ca. 490-460 Ma). This belt includes the Famatinian Cordilleran-type magmatic arc active mainly at ca. 473-468 Ma, coeval with andesite to rhyolitic volcanism (Suri and Las Planchadas formations). Rhyolitic tuffs of ca. 473 Ma (epsilon Ndi = - 4.1) were found in the La Aguadita Formation, allowing this unit to be re-assigned to the late Floian. The oldest magmatism of the Sierra de Famatina is characterized by isotopically evolved (epsilon Ndi = - 5.1) rhyolitic tuffs of ca. 490 Ma in the Bordo Atravesado Formation, which was coeval with deposition of Mn-enriched hydrothermal cherts. This early Famatinan volcanism contrast with that of similar age and isotopically less evolved occurred in the Calalaste-Narv & aacute;ez Lithotectonic Belt suggesting variations of the source of magmas across the space and time within the Famatinan Orogenic Cycle. We propose that both described lithotectonic belts likely diverge northwards into Chile and Peru, wrapping around the Arequipa-Antofalla Proterozoic block.