Crustal-to-mantle shifting in SiO2-rich upper crustal magmas through zircon and bulk rock compositions in the Famatinian arc, Argentina

Abstract The Famatinian arc (northwestern Argentina), an early Paleozoic continental margin along Gondwana, preserves an exceptional window into the upper crustal magmatism in the Chaschuil section. New zircon U-Pb dating, trace elements, and O-Hf isotope analyses, coupled with bulk rock chemistry and field relationships, unravel two distinct magmatic stages during arc development. The initial magmatic column construction during 490–478 Ma formed the strongly peraluminous granites of the Narváez batholith, with high δ18OZircon values (~7.5‰–9.6‰) and negative εHf(t) signatures (~−6.3 to −0.6). This stage preceded a high-magma-flux event at 470 ± 3 Ma, which led to the development of the Las Planchadas Plutonic-Volcanic Complex. This complex comprises a weakly peraluminous granite-rhyolite sequence, distinguished by a shift toward lower δ18OZircon (4.0‰–5.8‰) and positive εHf(t) values (0.0 to +7.6). Zircon εHf-δ18O arrays define mixing and assimilation–fractional crystallization trends indicating early assimilation of turbidite sequences followed by advanced crystallization of uncontaminated mantle melts. Progressive magma chamber growth shielded (or exhausted) fertile crust, restricting crustal melt influx. Our findings elucidate the dynamic mantle-crust interplay during arc maturation, underscoring the key role of pre-existing lithospheric architecture (metasedimentary versus igneous) in shaping magmatic diversity.