Earth and Planetary Science

Graphite‑Rich Phyllonitic Metapelites and Metamafic Rocks from the Itatiaiuçu Region of Southern Sao Francisco Craton: Remnants of Paleoproterozoic Forearc Basin

Raphael Martins Coelho

Federal University of Minas Gerais (UFMG, Postgraduate Program in Geology), Institute of Geosciences

Alexandre de Oliveira Chaves

Institute of Geosciences, Federal University of Minas Gerais, Belo Horizonte 31270‑901, Brazil

Roberto Moreno Prado Pereira

Institute of Geosciences, Federal University of Minas Gerais, Belo Horizonte 31270‑901, Brazil

Carla Cristine Porcher

Institute of Geosciences, Federal University of Rio Grande do Sul, Porto Alegre 90650‑001, Brazil

DOI: https://doi.org/10.36956/eps.v5i1.3040

Received: 29 December 2025; Published: 30 March 2026

Abstract

The area in the southern São Francisco Craton, between Itatiaiuçu and Rio Manso (Minas Gerais), constitutes a geological domain that remains poorly constrained regarding the nature, age, and tectono-metamorphic evolution of its metamafic and metasedimentary units. A marked contrast in gamma-spectrometric signatures—expressed by darker tones relative to the surrounding Archean terranes—delineates a distinct lithological association composed of tremolite–actinolite schists, metaconglomerates with strongly stretched clasts, and phyllonitic metapelites containing quartz, graphite (δ13C values between −26‰ and −14‰, consistent with an organic source), plagioclase, chlorite, phengite, amphibole, and garnet. The tremolite–actinolite schists yield paleoproterozoic Sm–Nd model ages between 2,354 and 2,110 Ma and positive εNd values (+0.56 to +3.53), indicating derivation from a mantle source. Mineral assemblages in the phyllonitic metapelites are compatible with metamorphism of a flysch–molasse-type mélange developed in a forearc basin associated with subduction-related shear processes within an accretionary orogen. In this framework, the tremolite–actinolite schists are interpreted as metamorphosed oceanic crust, representing remnants of an oceanic domain that separated the Campo Belo–Bonfim and Belo Horizonte blocks around 2.3 Ga. The transition from oceanic to forearc basin conditions was accompanied by deformation within a thrust belt, where flysch and molasse sequences were metamorphosed to produce phyllonitic metapelites and metaconglomerates. Collectively, this domain preserves significant evidence of Paleoproterozoic geodynamic processes comparable to those observed in modern convergent plate settings.

Keywords: Itatiaiuçu, Tremolite‑Actinolite Schists and Phyllonitic Metapelites, Flysch‑Molasse‑Type Mélange, Forearc Basin, Paleoproterozoic

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