Prolonged high-temperature granite production following subduction-accretion episodes at Ribeira belt, SE Brazil

The Pan-African/Brasiliano orogeny, result of the West-Gondwana assembly from the Neoproterozoic to the Early Paleozoic, culminated in a widespread, long-lived Ediacaran to Cambro-Ordovician collisional to post-collisional granite production event at the Araçuaí-Ribeira Orogenic System. Collisional granitoids were emplaced along an interval wider than 100 m.y., following three different subduction-accretion episodes. The syn- to late-collisional Serra dos Órgãos batholith is the main granitoid intrusion emplaced following the major subduction-accretion episode at the central Ribeira belt, southeastern Brazil. The integration of zircon in-situ LA-MC-ICP-MS trace elements and Lu-Hf isotopes, EMPA mineral chemistry and whole-rock ID-TIMS Sm-Nd and Rb-Sr isotopes were employed to constraint the physical-chemical conditions concerning the pre-collisional to the earlier stages of the collisional period, just after the main subduction-accretion completion. For this purpose, sensu stricto granites from Serra dos Órgãos batholith and from country rocks were examined. Whole-rock and zircon in-situ radiogenic isotopes results reveal multi-component inheritance in both Serra dos Órgãos granites and in the country rock granitic leucogneisses. The studied granitic Leucogneisses recorded diverse zircon populations with juvenile to mature arc-crust Nd–Sr–Hf isotopic signatures in a large span of geochronological ages (100 m.y. interval). Hence, the granitic Leucogneisses behaved as a temporal archive of the pre-collisional period after the partial melting of heterogeneous or multiple sources. On the other hand, the zircon populations observed in the medium- to coarse-grained granitoids of the Serra dos Órgãos batholith present the characteristics of newly crystallized zircons from a homogeneous source experiencing disequilibrium melting: a main zircon population interpreted as autocrystic (ca. 590 Ma), and minor inheritance given by an antecrystic population (ca. 610 – 620 Ma). The less spanned geochronological ages (ca. 590 Ma, hornblende-biotite granitoids) and more homogeneous isotopic signatures for Nd–Sr–Hf, along with the presence of antecrystic zircon population (ca. 620 Ma antecrystals in hornblende-biotite granitoids) and inherited/xenocrystic zircon population (ca. 1.9 Ga xenocrystals in leucogranites) are evidence of zircon preservation in disequilibrium melting situations. The inheritance patterns reinforce the hypothesis of distinct sources for the granitic Leucogneisses and granites to leucogranites of the Serra do Órgãos. Hornblende-plagioclase and Ti-in-zircon temperatures strongly suggest thermal disequilibrium between zircon and magmas, consistent with the presence of antecrystic and inherited zircon populations, distinguished by U-Pb geochronology and Nd–Sr–Hf isotopic signatures. Ti-in-zircon thermometry suggests early crystallization temperatures for zircon precipitation, while hornblende-plagioclase geothermometry yields near-solidus, late crystallization temperatures in the Serra dos Órgãos granites. REE-in-zircon oxybarometry suggests fO₂ around FMQ conditions for the Serra dos Órgãos granites, contrasting with more oxidized fO₂ conditions for the pre-collisional granitic leucogneisses. The pieces of evidence indicate that the sensu stricto granites of the Serra dos Órgãos batholith were formed by water-undersaturated melting of previously formed crust at temperatures around 810 – 820 °C. Furthermore, the pre-collisional sensu stricto granites from country rocks record a ca. 830 Ma event which discloses juvenile magma production more than 200 m.y. before the Serra dos Órgãos emplacement and the West Gondwana amalgamation.