The role of mantle–crustal sources in the genesis of the San Feliciano Plutonic System (SFPS), Concepcion del Oro, Zacatecas (Cretaceous): Insights from Geochemistry, Sm–Nd isotopes, and U–Pb geochronology

Abstract

The San Feliciano Plutonic System (SFPS) is located south of Concepcion del Oro, Zacatecas, Mexico, and is emplaced within a Mesozoic marine sedimentary sequence as part of the Concepcion del Oro Intrusive Belt (COIB). This region is historically recognized for its abundant mineral resources, including gold (Au), silver (Ag), lead (Pb), zinc (Zn), and copper (Cu). The mineralogical assemblage of the SFPS consists of moderately altered phenocrysts of plagioclase and potassium feldspar, with lesser amounts of quartz. Hornblende is present in moderate quantities, accompanied by clinopyroxene, apatite, biotite, and magnetite. The presence of secondary minerals such as calcite, sericite, quartz, secondary feldspar, pyrite and oxides reflect varying degrees of hydrothermal alteration. The SFPS exhibits an intermediate composition (SiO_2(adj) = 52.39–66.37 wt%), ranging from monzonite/quartz monzonite to diorite and syenite, which is consistent with an I-type granitoid signature. Chondrite-normalized Rare Earth Element (REE) patterns reveal enrichment in Light Rare Earth Elements (LREE) relative to Heavy Rare Earth Elements (HREE). Geochemical data suggest that the magma originated from partial melting, followed by fractional crystallization and assimilation during its evolution, before being emplaced into the middle to upper continental crust. Whole-rock isotopic data indicates that the magma originated from partial melting of a depleted mantle source, accompanied by interaction with continental crust. This interpretation is supported by εNd values ranging from +2.0 to +3.6 and model ages around 0.5 Ga at t = 74.3 Ma (average age). U–Pb geochronology constrains the crystallization age of the plutonic system to between 83.49 ± 3.25 Ma and 69.31 ± 2.30 Ma, placing the SFPS in the Late Cretaceous (Santonian-Campanian). The tectonic model suggests that the magma was generated in a continental volcanic arc setting, associated with syn-tectonic magmatism during active crustal deformation. Additionally, there is also evidence of pre-magmatic activity on the western side of the COIB, contemporaneous with magmatism on the eastern side. This tectonomagmatic evolution is linked to the subduction of the Farallon Plate beneath the North American Plate from the Late Cretaceous to the Paleogene, during the development of the Cretaceous–Eocene Mexican Magmatic Arc (CEMMA).