Genetic Relationship between Subduction of Slab Topographic Anomalies and Porphyry Deposit Formation: Insight from the Source and Evolution of Rio Blanco Magmas

Abstract The Rio Blanco deposit, which is one of the largest porphyry Cu–Mo deposits in northern Peru, formed coevally with subduction Inca Oceanic Plateau at 12–10 Ma. However, genetic relationship between oceanic plateaus and deposit formation remains unclear. Igneous rocks emplaced 23–12 Ma including Portachuela batholith (which hosts complex), are normal calc-alkaline to weakly adakitic. In comparison, 12–8 igneous rocks, ore-related complex, have typical adakitic signatures, such as high Sr/Y ratios (up 180) LaN/YbN 32). (Portachuela complex) uniform zircon εHf(t) values (+0.3 ± 1.2) δ18O (6.5 0.14‰). These geochemical characteristics indicate that evolved from mantle-derived parental melts a long-lived, stable, homogeneous isotopic reservoir crust–mantle boundary. whereas both complex hydrous magmas (>5 wt %; based on plagioclase hygrometry), ones seem be more oxidized, hydrous, sulfur-rich compared older batholitic rocks. Reverse zoning phenocrysts, systematic core–mantle–rim variation An (anorthite) Fe (total iron) contents, common intermineralization content mantles phenocrysts correlates positively content, but rims, contents significantly decrease while constant. apatite inclusions richer S (0.24 0.06 %) Cl (1.42 0.32 than those phenocryst cores (S: 0.09 0.07 Cl: 1.03 0.56 rims 0.14 0.83 0. 35 %). systemic variations suggest recharge by S- Cl-rich followed fluid exsolution. This magma subsequent exsolution may triggered Cu mineralization Blanco. coincidence timing transition collision (initial subduction) South American plate change tectonic regime compressional state stress thickening crust during collision. would facilitated fractionation deep crustal hot zone, resulting volatile-rich residual melts. Replenishment upper-crustal chamber discharge fluids interpreted fundamental for plausibly Late Miocene ore Peru general.