Source diversity of Late Neoproterozoic granitoid magmatism across an orogen-scale lineament in southern Brazil and Uruguay: Whole-rock geochemistry, zircon geochronology and Sr-Nd-Hf isotope evidence

Abstract

Granitoids of similar Brasiliano age (638–540 Ma) are widespread in southern Brazil and Uruguay on both sides of an orogen-parallel lineament comprising from south to north, the Sierra Ballena, Dorsal de Canguçu and Major Gercino shear zones. We reviewed mineralogy, geochemistry and geochronology of granitoids that occur in the two domains located east and west of the mentioned lineament. Most of the granitoid magmatism is calc-alkalic to alkali-calcic and magnesian to ferroan, but variations are observed (aluminosity increases in eastern relative to western domain granitoids, and alkaline intrusions are more frequent in the western domain). Considering mineralogy and geochemistry the K-rich calc-alkaline granitoids (KCG) type of Barbarin's predominate, but amphibole-rich calc-alkaline granitoids (ACG), muscovite-bearing peraluminous granitoids (MPG) and peralkaline and alkaline granitoids (PAG) type affinities (although subordinate) do also occur. High-barium-strontium (HiBaSr) granitoids (with and without shoshonitic affinity) are frequent in the western but sporadic in the eastern domain. Granitoids intruding in the western domains of Santa Catarina, Rio Grande do Sul and Uruguay generally display crystallization ages between 638 and 540 Ma, Archaean to Neoproterozoic inherited zircon ages (3365–640 Ma) and strongly evolved isotopic signatures and model ages (ϵNd600 of −8.5 to −32; Nd TDM2 ages of 1.9–3.7 Ga; ϵHf (t) of −0.46 to −35.7 and Hf TDMCrustal ages of 1.5–3.6 Ga). Granitoids from the eastern domain, while showing a similar range of crystallization ages (630–543 Ma), generally reveal contrastingly younger inherited zircon ages (774–642 Ma) and less evolved isotope characteristics and model ages (ϵNd600 of −2.3 to – 11.8, Nd TDM2 of 1.4–2.1 Ga; ϵHf(t) of −0.21 to −12.5 and Hf TDMCrustal ages of 1.5–2.4 Ga).The assessment of the data compiled for this contribution indicate that: a) in southern Brazil and Uruguay, the Sierra Ballena-Dorsal de Canguçu-Major Gercino Lineament, act as a remarkable tectonic regional boundary between domains whose granitoids generally (but not always) show a pattern of contrasting whole-rock key chemical indicators, zircon inheritance, isotope signatures and model ages reflecting different granitoid sources; b) granitic melt production took place from the interaction of sources of different age (e.g. old Archaean to Paleoproterozoic crust and/or of Tonian age arc-materials) and composition (e.g. crustal sources: metaigneous rocks, metasediments vs. mantle-derived sources: juvenile basaltic melts and/or metasomatized mantle); c) crustal components strongly outweigh mantle ones in the source of the granitoids, suggesting that recycling was the chief mechanism; d) however, the spatial association of plutonic intermediate to basic rocks and felsic granitoids is sometimes significant in some sectors of southern Brazil and may be indicative of the adding up of new material from the mantle (i.e “crustal growth” processes) to the crust within a post-collisional environment.