The late Ediacaran to early Cambrian subduction-related granitic magmatism of the Pampean orogen: Geochemical and isotopic constraints on hybridization processes

Abstract

The late Ediacaran to early Cambrian Pampean magmatic arc in Argentina represents an excellent example of subduction-related magmatism and continental crust formation. This study presents new geochemical, isotopic, and geochronological data from the Guasayán intrusive complex, which is a significant body within this magmatic arc. The data are integrated with a comprehensive compilation of published data from the arc elsewhere. The Pampean arc exhibits a wide range of rocks, from metaluminous I-type diorites to strongly peraluminous S-type granites, with the majority displaying hybrid compositions (mostly magnesian, calc-alkalic and slightly peraluminous compositions). Zircon U-Pb geochronology indicates that the Guasayán granitoids were emplaced mainly during a flare-up of arc magmatism between ca. 530 and 535 Ma. However, the presence of zircon antecrysts with ages of ca. 545 Ma in most of the Pampean arc granitoids, suggests that the magmatic system was long-lived, and the early crystallized zircon crystals were recycled into younger magmatic pulses. Geochemical and isotope data (Sr-Nd-Hf) highlight the interaction between mantle-derived magmas and crustal components, with magma mixing identified as the dominant process in the generation of the hybrid granitoids. Local-scale processes such as crustal assimilation, fractional crystallization, and peritectic entrainment also contributed to the geochemical and isotopic diversity. The involvement of the Puncoviscana Series as the crustal component of the mixed magmas is evidenced by zircon inheritance patterns and isotopic signatures. This study underscores the importance of magma mixing in the evolution of the Pampean arc and provides insights into the geodynamic processes driving continental crust formation in subduction-related settings.