Tracking the sources and the evolution of the late Neoproterozoic granitic intrusions in the Brusque Group, Dom Feliciano Belt, South Brazil: LA-ICP-MS and SHRIMP geochronology coupled to Hf isotopic analysis

Abstract

The central Domain of the Neoproterozoic Dom Feliciano Belt in the Brazilian state of Santa Catarina is mainly composed of a metavolcano-sedimentary sequence, the Brusque Group, and its crystalline basement, such as the Camboriú Complex. This association was intruded in its late-deformational stage by voluminous granitic magmatism, related to the metamorphic climax of the area. The intrusions share a distinct crustal affinity and are divided into three suites, from oldest to youngest, as indicated by field criteria: São João Batista, Valsungana and Nova Trento. We present seven new LA-ICP-MS and two SHRIMP U-Pb zircon ages, coupled with in-situ analysis of Hf isotopes, and use them to discuss the magmatic sources and evolution of the intrusions, and propose an evolutionary model for this plutonic association. Intrusion mostly took place at 615–585 Ma, but the field stratigraphy is not necessarily reflected by U-Pb ages, which establish considerable overlaps between intrusions from different suites. Inherited zircon crystals are common, and reflect a long geological history that matches the geochronological record of the Brusque Group and the Camboriú Complex. Hf ratios are remarkably widespread, but strengthen the characteristic crustal signature of the magmatism, and partially overlap with whole-rock isotopic data for the same rocks. We propose that the intrusions were caused by a regional heating event within the central domain of the Dom Feliciano Belt in Santa Catarina, with limited direct mantellic contribution and more significant indirect thermal contribution through the voluminous magmatism of the recently juxtaposed Florianópolis Batholith. This triggered large-scale partial melting of the local continental crustal and formed the studied granites. The long-lasting magmatic event promoted the protracted generation and emplacement of numerous distinct intrusions synchronically, leading to contrasts between the field and U-Pb stratigraphy. The suites’ varied geochemical and isotopic characteristics probably reflect a combination of the heterogeneities of their source rocks with the impact of different magmatic processes during granitogenesis and emplacement. While the Valsungana and Nova Trento suites were probably generated within a deeper crustal level and underwent some degree of magmatic interaction, the peraluminous São João Batista Suite has an upper-crust signature that indicates the assimilation of metasedimentary rocks.