The Faja Eruptiva of the Eastern Puna and the Sierra de Calalaste, NW Argentina: U–Pb zircon chronology of the early Famatinan orogeny

Abstract

The Famatinian is a segment of the Ordovician Terra Australis accretionary orogen that stretched along the SW Margin of Gondwana from Australia to Colombia. The present knowledge of this orogenic segment still is incomplete. We present geochemistry and U–Pb SHRIMP zircon geochronology of igneous and metamorphic rocks from the Central Famatinian Domain, one of the several domains recognized by Rapela et al. (Earth Sci Rev 187: 259–285. https://doi.org/10.1016/j.earscirev.2018.10.006) that includes the northern Sierras Pampeanas and the southern Puna of North West Argentina. Six samples of igneous rocks (peraluminous granitoids, mafic and felsic rocks, volcanic/subvolcanic rocks) and six samples of associated meta-sedimentary rocks, all from the Puna were dated and chemically analysed. The results indicate that the Central Famatinian Domain is in turn a composite domain that includes a Cordilleran-type magmatic arc (ca. 470 Ma) and a yuxtaposed fault-bounded older terrain formed in an extensional setting at the very start of the Famatinian orogeny, between 480 and 485 Ma, i.e., shortly after the SW Gondwana margin switched from passive to active. This short period of extension with related sedimentation, volcanism and mainly granitoid plutonism has not been previously recognised. It occurred before the Cordilleran-type magmatic arc -that resulted from a magmatic flare-up between ca. 473 and 468 Ma-, set up coincident with a contractional phase. The evidence confirms that accretionary orogeny results from tectonic switching (pull–push orogeny) and that the extensional and contractional phases are of relatively short duration.