Constraints from mantle composition on petrogenesis of Neoarchean charnockite from Carajás Province, Amazonian Craton, Brazil

Le résumé fourni par la source

Charnockitic magmatism records fundamental processes of crustal growth and stabilization in Archean cratons. In the Amazonian Craton, the Neoarchean Pium Suite represents a key magmatic event for understanding crust-mantle interactions in the Carajás Province, Amazonian Craton. This study formally establishes the suite, comprising three intrusive units, the Pium norite, the Café enderbite, and the Rio Seco charnockite. U-Pb zircon geochronology constrains the crystallization of these syntectonic units (2.75–2.73 Ga). Combined whole-rock Sm-Nd and zircon Lu-Hf data reveal a marked isotopic dichotomy: the Rio Seco charnockite exhibits predominantly juvenile signatures ( ε Nd ( t ) up to + 0.6; ε Hf ( t ) up to + 2.0) derived from a depleted-mantle source, whereas the Pium norite and Café enderbite display evolved signatures ( ε Nd ( t ) = –2.8 to –1.0; ε Hf ( t ) = –4.8 to –1.0) reflecting enriched-mantle sources with longer crustal residence times. This isotopic heterogeneity indicates that the subcontinental lithospheric mantle source was variably affected by ancient Mesoarchean metasomatism prior to the partial melting in the Neoarchean. Despite their different origins as spinel lherzolite, spinel peridotite, and mafic granulite, the units follow a convergent evolutionary trajectory influenced primarily by fractional crystallization. Mineral chemistry constraints indicate crystallization under high temperatures (710–1573 °C), oxidizing conditions, and pressures of 200–600 MPa. The geochemical signatures, high crystallization temperatures, and syntectonic emplacement of the Pium Suite are consistent with a post-collisional setting involving crust-mantle delamination, indicating the final stabilization of the Archean crust in the Carajás Province. This magmatic event emphasizes the importance of mantle heterogeneity and lithospheric processes in Neoarchean cratonization.

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