Timing and origin of the post-collisional Venda Nova and Várzea Alegre Plutons from the Araçuaí belt, Espírito Santo, Brazil.

The Venda Nova and Várzea Alegre Plutons in southeastern Brazil are post-collisional complexes formed during the gravitational collapse of the Araçuaí-Ribeira orogenic system during amalgamation of SW Gondwana. This study focuses on the petrological, geochemical, geochronological and zircon Lu-Hf isotopic signatures of both plutons to constrain and complete their ages and to characterize mantle vs. crustal source components. The Venda Nova Pluton is divided into an inner, mildly alkaline, and an outer, calc-alkaline domain. One diorite, three quartz syenites and two granites from the inner domain give LA-ICP-MS zircon U-Pb ages of 492–477 ± 8 Ma. The outer domain is dominated by charnockites and norites, six measured charnockites give two zircon ages of 620–606 ± 11 Ma and 500–476 ± 14 Ma, corresponding to zircon core and rim, respectively; the only norite yielding zircons gives a nominal age of 567 ± 13 Ma, which cannot be simply interpreted as emplacement age. The various intrusives from the Várzea Alegre Pluton (gabbronorites, charnockites, monzogranites, syenogranites) straddle the alkaline to calc-alkaline affinity and yield all together a uniform age of 500 ± 8 Ma. This confirms that all lithologies from the Venda Nova inner domain and Várzea Alegre Pluton belong to the post-collisional G5 suite of this region. The Venda Nova outer domain charnockites, fit age-wise into the pre-collisional arc-related magmatism (G1 suite). The zircon rim ages obtained on these charnockites represent minor fluid-assisted partial remelting and resetting of the U-Pb system during the emplacement of the inner domain. Individual norite zircons show ages ranging from the charnockite intrusion age to the metamorphic thermal peak in this region. The Lu-Hf isotopes measured on the dated zircon crystals, yield mantle values for the charnockites from the Venda Nova outer domain (εHf: 3.4 ± 1.2 to 6.8 ± 1.5), indicating an isotopically depleted mantle source, consistent with arc magmatism. Instead, the Venda Nova inner domain and the Várzea Alegre Pluton have relatively radiogenic values (εHf: −12.3 ± 1.5 to −8.8 ± 2.9 and − 11.1 ± 1.1 to −7.4 ± 1.3, respectively) and show no significant variation between all lithologies, indicating a source dominated by a previously crustally enriched mantle with only minor crustal assimilation occurring during magma emplacement. Interestingly, the charnockite rim of Venda Nova is 100 Ma older than the inner (mildly alkaline) post-orogenic domain and belongs to the pre-orogenic calc-alkaline arc suite, while the charnockite ring at Várzea Alegre is part of the intrusion, both in time and geochemistry, and shows no increased crustal signature with respect to the rest of the pluton. • Age and magmatic source constrain of Venda Nova and Várzea Alegre Pluton. • Venda Nova inner domain + entire Várzea Alegre are post-orogenic (G5, ∼500 Ma). • G5-suite melts derive from a previously crustal enriched lithospheric mantle. • Venda Nova calc-alkaline charnockite rim (G1, ∼610 Ma) derived from depleted mantle. • Constant εHf with differentiation suggests minor crustal assimilation. [ABSTRACT FROM AUTHOR]