The late- to postorogenic transition in the Neoproterozoic Agudos Grandes Granite Batholith (Apiaí Domain, SE Brazil): Constraints from geology, mineralogy, and U–Pb geochronology

Abstract

The latest evolution of the Neoproterozoic Agudos Grandes Batholith (Apiaí domain, SE Brazil) is marked by an important change in the type of granitic magmatism. The “late-orogenic” Piedade, Roseira, Serra dos Lopes, and Pilar do Sul granites are elliptical plutons with roughly concentric zoning and a spatial arrangement suggesting a continuous southwestward migration of the magmatic focus. The main rock types are “contaminated” calc-alkaline granites that range from mafic-rich (color index > 10), porphyritic biotite (±muscovite) granite-granodiorite in Piedade to pink, equigranular, muscovite–biotite leucogranite (CI < 5) strongly affected by hydrothermal effects in Pilar do Sul. U–Pb monazite dating indicates that these plutons were emplaced during 600–605 Ma, slightly after the main “synorogenic” magmatic stage (615–610 Ma), which was dominated by high-K, calc-alkaline, metaluminous, porphyritic hornblende-biotite granites with minor peraluminous leucogranite bodies. The “postorogenic” granites are divided into two groups on the basis of pluton shapes and U–Pb dating, both with “A-type” affinities. The approximately 585 Ma group (São Miguel Arcanjo and Capão Bonito granites) relates to the Itu granitic province, which developed around 10 m.y. after the cessation of the main regional compressional events, and cross-cuts the reworked border of the Paranapanema plate; the younger, approximately 565 Ma group is represented by two elongated plutons (Serra da Batéia and Serra da Queimada) that seem to reflect coeval orogenic events farther east in the Ribeira belt. The modal composition, magnetic susceptibility, and mafic mineral chemistry of the late-orogenic granites are consistent with an origin by contamination of metaluminous, oxidized, calc-alkaline magmas with crustal melts.