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

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

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 | Revised: 27 February 2026 | Accepted: 12 March 2026 | Published Online: 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

---

References

[1] Bahlburg, H., Vervoort, J.D., Du Frane, S.A., et al., 2009. Timing of crust formation and recycling in accretionary orogens: Insights learned from the western margin of South America. Earth-Science Reviews. 97(1–4), 215–241. DOI: https://doi.org/10.1016/j.earscirev.2009.10.006

[2] Sepidbar, F., Ao, S., Palin, R.M., et al., 2019. Origin, age and petrogenesis of barren (low-grade) granitoids from the Bezenjan-Bardsir magmatic complex, southeast of the Urumieh-Dokhtar magmatic belt, Iran. Ore Geology Reviews. 104, 132–147. DOI: https://doi.org/10.1016/j.oregeorev.2018.10.008

[3] Thakur, V.C., Misra, D.K., 1984. Tectonic framework of the Indus and Shyok suture zones in Eastern Ladakh, Northwest Himalaya. Tectonophysics. 101(3–4), 207–220. DOI: https://doi.org/10.1016/0040-1951(84)90114-8

[4] Robertson, A.H.F., 2000. Formation of mélanges in the Indus Suture Zone, Ladakh Himalaya by successive subduction-related, collisional and post-collisional processes during Late Mesozoic-Late Tertiary time. Geological Society, London, Special Publications. 170(1), 333–374. DOI: https://doi.org/10.1144/GSL.SP.2000.170.01.19

[5] Palin, R.M., Searle, M.P., St-Onge, M.R., et al., 2015. Two-stage cooling history of pelitic and semi-pelitic mylonite (sensu lato) from the Dongjiu–Milin shear zone, northwest flank of the eastern Himalayan syntaxis. Gondwana Research. 28(2), 509–530. DOI: https://doi.org/10.1016/j.gr.2014.07.009

[6] Parsons, A.J., Hosseini, K., Palin, R.M., et al., 2020. Geological, geophysical and plate kinematic constraints for models of the India-Asia collision and the post-Triassic central Tethys oceans. Earth-Science Reviews. 208, 103084. DOI: https://doi.org/10.1016/j.earscirev.2020.103084

[7] De Jong, K., 2003. Very fast exhumation of high-pressure metamorphic rocks with excess 40Ar and inherited 87Sr, Betic Cordilleras, southern Spain. Lithos. 70(3–4), 91–110. DOI: https://doi.org/10.1016/S0024-4937(03)00094-X

[8] Bröcker, M., Bieling, D., Hacker, B., et al., 2004. High‐Si phengite records the time of greenschist facies overprinting: implications for models suggesting mega‐detachments in the Aegean Sea. Journal of Metamorphic Geology. 22(5), 427–442. DOI: https://doi.org/10.1111/j.1525-1314.2004.00524.x

[9] Dowe, D.S., Nance, R.D., Keppie, J.D., et al., 2005. Deformational History of the Granjeno Schist, Ciudad Victoria, Mexico: Constraints on the Closure of the Rheic Ocean? International Geology Review. 47(9), 920–937. DOI: https://doi.org/10.2747/0020-6814.47.9.920

[10] Hervé Allamand, F.E.I., Calderón, M., Faúndez, V., 2008. The metamorphic complexes of the Patagonian and Fuegian Andes. Geologica Acta. 43–53. DOI: https://doi.org/10.1344/105.000000240

[11] Ukar, E., Cloos, M., 2016. Graphite‐schist blocks in the Franciscan Mélange, San Simeon, California: Evidence of high‐ P metamorphism. Journal of Metamorphic Geology. 34(3), 191–208. DOI: https://doi.org/10.1111/jmg.12174

[12] De Oliveira Chaves, A., Alexandre Goulart, L.E., Coelho, R.M., et al., 2019. High-pressure eclogite facies metamorphism and decompression melting recorded in paleoproterozoic accretionary wedge adjacent to probable ophiolite from Itaguara (southern São Francisco Craton - Brazil). Journal of South American Earth Sciences. 94, 102226. DOI: https://doi.org/10.1016/j.jsames.2019.102226

[13] De Oliveira Chaves, A., Porcher, C.C., 2020. Petrology, geochemistry and Sm-Nd systematics of the Paleoproterozoic Itaguara retroeclogite from São Francisco/Congo Craton: One of the oldest records of the modern-style plate tectonics. Gondwana Research. 87, 224–237. DOI: https://doi.org/10.1016/j.gr.2020.06.014

[14] CPRM—Brazilian Geological Survey, CODEMIG—Economic Development Company of Minas Gerais, 2014. Geological Map of the State of Minas Gerais. Scale 1:1,000,000 DVD-rom. CPRM, CODEMIG: Belo Horizonte, Brazil. (in Portuguese)

[15] Teixeira, W., Ávila, C.A., Dussin, I.A., et al., 2015. A juvenile accretion episode (2.35–2.32Ga) in the Mineiro belt and its role to the Minas accretionary orogeny: Zircon U–Pb–Hf and geochemical evidences. Precambrian Research. 256, 148–169. DOI: https://doi.org/10.1016/j.precamres.2014.11.009

[16] Baltazar, O.F., Zucchetti, M., 2007. Lithofacies associations and structural evolution of the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil: A review of the setting of gold deposits. Ore Geology Reviews. 32(3–4), 471–499. DOI: https://doi.org/10.1016/j.oregeorev.2005.03.021

[17] Machado, N., Schrank, A., Noce, C.M., et al., 1996. Ages of detrital zircon from Archean-Paleoproterozoic sequences: Implications for Greenstone Belt setting and evolution of a Transamazonian foreland basin in Quadrilátero Ferrífero, southeast Brazil. Earth and Planetary Science Letters. 141(1–4), 259–276. DOI: https://doi.org/10.1016/0012-821X(96)00054-4

[18] Martínez Dopico, C.I., Lana, C., Moreira, H.S., et al., 2017. U–Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil. Precambrian Research. 291, 143–161. DOI: https://doi.org/10.1016/j.precamres.2017.01.026

[19] Machado Filho, L., Ribeiro, M.W., Gonzalez, S.R., et al., 1983. Geology. In RADAMBRAZIL Project. Ministry of Mines and Energy, Secretariat-General: Rio de Janeiro, Brazil. pp. 36–45. (in Portuguese)

[20] Lana, C., Alkmim, F.F., Armstrong, R., et al., 2013. The ancestry and magmatic evolution of Archaean TTG rocks of the Quadrilátero Ferrífero province, southeast Brazil. Precambrian Research. 231, 157–173. DOI: https://doi.org/10.1016/j.precamres.2013.03.008

[21] Romano, R., Lana, C., Alkmim, F.F., et al., 2013. Stabilization of the southern portion of the São Francisco craton, SE Brazil, through a long-lived period of potassic magmatism. Precambrian Research. 224, 143–159. DOI: https://doi.org/10.1016/j.precamres.2012.09.002

[22] Farina, F., Albert, C., Martínez Dopico, C., et al., 2016. The Archean–Paleoproterozoic evolution of the Quadrilátero Ferrífero (Brasil): Current models and open questions. Journal of South American Earth Sciences. 68, 4–21. DOI: https://doi.org/10.1016/j.jsames.2015.10.015

[23] Moreira, H., Lana, C., Nalini, H.A., 2016. The detrital zircon record of an Archaean convergent basin in the Southern São Francisco Craton, Brazil. Precambrian Research. 275, 84–99. DOI: https://doi.org/10.1016/j.precamres.2015.12.015

[24] Ávila, C.A., Teixeira, W., Cordani, U.G., et al., 2010. Rhyacian (2.23–2.20Ga) juvenile accretion in the southern São Francisco craton, Brazil: Geochemical and isotopic evidence from the Serrinha magmatic suite, Mineiro belt. Journal of South American Earth Sciences. 29(2), 464–482. DOI: https://doi.org/10.1016/j.jsames.2009.07.009

[25] Alkmim, F.F., Teixeira, W., 2017. The Paleoproterozoic Mineiro Belt and the Quadrilátero Ferrífero. In: Heilbron, M., Cordani, U.G., Alkmim, F.F. (Eds.). São Francisco Craton, Eastern Brazil, Regional Geology Reviews. Springer International Publishing: Cham, Switzerland. pp. 71–94. DOI: https://doi.org/10.1007/978-3-319-01715-0_5

[26] Bruno, H., Heilbron, M., De Morisson Valeriano, C., et al., 2021. Evidence for a complex accretionary history preceding the amalgamation of Columbia: The Rhyacian Minas-Bahia Orogen, southern São Francisco Paleocontinent, Brazil. Gondwana Research. 92, 149–171. DOI: https://doi.org/10.1016/j.gr.2020.12.019

[27] Campos, J.C.S., Carneiro, M.A., 2008. Neoarchean and Paleoproterozoic granitoids marginal to the Jeceaba-Bom Sucesso lineament (SE border of the southern São Francisco craton): Genesis and tectonic evolution. Journal of South American Earth Sciences. 26(4), 463–484. DOI: https://doi.org/10.1016/j.jsames.2008.09.002

[28] Oliveira, A.H., 2004. Tectonic Evolution of a Fragment of the Southern São Francisco Craton [PhD Thesis]. Federal University of Ouro Preto: Ouro Preto, Brazil. (in Portuguese)

[29] Coelho, R.M., Chaves, A.D.O., 2019. Pressure-temperature-time path of Paleoproterozoic khondalites from Claudio shear zone (southern São Francisco craton, Brazil): Links with khondalite belt of the North China craton. Journal of South American Earth Sciences. 94, 102250. DOI: https://doi.org/10.1016/j.jsames.2019.102250

[30] Pereira, R.M.P., Lana, C.D.C., Porcher, C.C., et al., 2025. Ophiolitic metamafic remnants of Palaeoproterozoic oceanic crust from the Cláudio shear zone, Southern São Francisco Craton (Brazil). International Geology Review. 67(24), 2777–2801. DOI: https://doi.org/10.1080/00206814.2025.2563590

[31] Carvalho, B.B., Sawyer, E.W., Janasi, V.A., 2016. Crustal reworking in a shear zone: Transformation of metagranite to migmatite. Journal of Metamorphic Geology. 34(3), 237–264. DOI: https://doi.org/10.1111/jmg.12180

[32] Carvalho, B.B., Janasi, V.A., Sawyer, E.W., 2017. Evidence for Paleoproterozoic anatexis and crustal reworking of Archean crust in the São Francisco Craton, Brazil: A dating and isotopic study of the Kinawa migmatite. Precambrian Research. 291, 98–118. DOI: https://doi.org/10.1016/j.precamres.2017.01.019

[33] Teixeira, W., Oliveira, E.P., Peng, P., et al., 2017. U-Pb geochronology of the 2.0 Ga Itapecerica graphite-rich supracrustal succession in the São Francisco Craton: Tectonic matches with the North China Craton and paleogeographic inferences. Precambrian Research. 293, 91–111. DOI: https://doi.org/10.1016/j.precamres.2017.02.021

[34] Miranda, D.A., De Oliveira Chaves, A., Campello, M.S., et al., 2019. Origin and thermometry of graphites from Itapecerica supracrustal succession of the southern Sao Francisco Craton by C isotopes, X-ray diffraction, and Raman spectroscopy. International Geology Review. 61(15), 1864–1875. DOI: https://doi.org/10.1080/00206814.2018.1564073

[35] Miranda, D.A., Chaves, A.D.O., Dussin, I.A., et al., 2021. Paleoproterozoic khondalites in Brazil: a case study of metamorphism and anatexis in khondalites from Itapecerica supracrustal succession of the southern São Francisco Craton. International Geology Review. 63(4), 397–421. DOI: https://doi.org/10.1080/00206814.2020.1716273

[36] Goulart, L.E.A., Carneiro, M.A., 2010. Paleoproterozoic mafic–ultramafic magmatism in the southern São Francisco Craton: The Itaguara layered sequence. In Proceedings of the Brazilian Geological Congress, Belém, Brazil, 26 September–1 October 2010. (in Portuguese)

[37] Goulart, L.E.A., Carneiro, M.A., 2008. General characteristics and lithogeochemistry of the Itaguara layered ultramafic–mafic sequence, southern São Francisco craton. Geochimica Brasiliensis. 22, 45–72.

[38] Pinheiro, S.D.O., Nilson, A.A., 2000. Metakomatiitic and Meta-Ultramafic Rocks from the Rio Manso Region, Minas Gerais: Geology Textures and Metamorphism. Revista Brasileira de Geociências. 30(3), 421–423.

[39] Barbosa, A.D.S., Chaves, A.D.O., 2022. Itaguara amphibolites with E-MORB signature: Probable Paleoproterozoic ophiolite members of the southern São Francisco craton. Geociências. 40(4), 853–861. DOI: https://doi.org/10.5016/geociencias.v40i04.16005 (in Portuguese)

[40] De Oliveira Chaves, A., 2024. 2.13 Ga Lawsonite/Barroisite-Bearing E-Morb Signature Metagabbro Associated with Spinel Metaperidotite from Itaguara (São Francisco Craton, Brazil): Oldest Blueschist-Facies Fragment of Oceanic Moho? Earth and Planetary Science. 3(2), 14–40. DOI: https://doi.org/10.36956/eps.v3i2.1068

[41] Young, R.A., 1993. The Rietveld Method. Oxford University Press: Oxford, UK.

[42] Janoušek, V., Farrow, C.M., Erban, V., 2006. Interpretation of Whole-rock Geochemical Data in Igneous Geochemistry: Introducing Geochemical Data Toolkit (GCDkit). Journal of Petrology. 47(6), 1255–1259. DOI: https://doi.org/10.1093/petrology/egl013

[43] Liew, T.C., Hofmann, A.W., 1988. Precambrian crustal components, plutonic associations, plate environment of the Hercynian Fold Belt of central Europe: Indications from a Nd and Sr isotopic study. Contributions to Mineralogy and Petrology. 98(2), 129–138. DOI: https://doi.org/10.1007/BF00402106

[44] Whitney, D.L., Evans, B.W., 2010. Abbreviations for names of rock-forming minerals. American Mineralogist. 95(1), 185–187. DOI: https://doi.org/10.2138/am.2010.3371

[45] Einsele, G., 2000. Sedimentary Basins: Evolution, Facies, and Sediment Budget, 2nd ed. Springer: London, UK.

[46] Miranda, D.A., Chaves, A.D.O., 2021. Itapecerica Metamafic-Ultramafic Rocks with E-Morb Signature: Ophiolitic Remnants of the Rhyacian-Orosirian Orogeny in Southern são Francisco Craton? Geociências. 40(1), 1–12. DOI: https://doi.org/10.5016/geociencias.v40i1.15375 (in Portuguese)