Brazil), the Eastern Brazilian Pegmatite Province and Related Mineral Resources

Downloaded from http://sp.lyellcollection.org/ by guest on April 30, 2019 Late Neoproterozoic–Cambrian granitic magmatism in the Araçuaı´ orogen (Brazil), the Eastern Brazilian Pegmatite Province and related mineral resources A. C. PEDROSA-SOARES1*, CRISTINA P. DE CAMPOS2, CARLOS NOCE1, LUIZ CARLOS SILVA3, TIAGO NOVO1, JORGE RONCATO1,SI´LVIA MEDEIROS4, CRISTIANE CASTAN˜ EDA1, GLA´ UCIA QUEIROGA1, ELTON DANTAS5, IVO DUSSIN1 & FERNANDO ALKMIM6 1Universidade Federal de Minas Gerais, IGC–CPMTC, Campus Pampulha, 31270-901 Belo Horizonte, MG, Brazil 2Department of Earth and Environmental Sciences – LMU Theresienstrasse 41/III – 80333, Munich, Germany 3Serviço Geolo´gico do Brasil–CPRM, Belo Horizonte, MG, Brazil 4Universidade Estadual do Rio de Janeiro, UERJ–Faculdade de Geologia, Rio de Janeiro, RJ, Brazil 5Universidade de Brası´lia, UnB–IG–Laborato´rio de Geocronologia, Asa Norte, Brası´lia, DF, Brazil 6Universidade Federal de Ouro Preto, DEGEO, Campus do Cruzeiro, Ouro Preto, Brazil *Corresponding author (e-mail: [email protected]) Abstract: The Araçuaı´ orogen extends from the eastern edge of the Saõ Francisco craton to the Atlantic margin, in southeastern Brazil. Orogenic igneous rocks, formed from c. 630 to c. 480 Ma, cover one third of this huge area, building up the Eastern Brazilian Pegmatite Province and the most important dimension stone province of Brazil. G1 supersuite (630–585 Ma) mainly consists of tonalite to granodiorite, with mafic to dioritic facies and enclaves, representing a continental calc-alkaline magmatic arc. G2 supersuite mostly includes S-type granites formed during the syn-collisional stage (585–560 Ma), from relatively shallow two-mica granites and related gem-rich pegmatites to deep garnet-biotite granites that are the site of yellow dimension stone deposits. The typical G3 rocks (545–525 Ma) are non-foliated garnet-cordierite leucogranites, making up autochthonous patches and veins. At the post-collisional stage (530–480 Ma), G4 and G5 supersuites were generated. The S-type G4 supersuite mostly consists of garnet-bearing two-mica leucogranites that are the source of many pegmatites mined for tourmalines and many other gems, lithium (spodumene) ore and industrial feldspar. G5 supersuite, consisting of high-K–Fe calc-alkaline to alkaline granitic and/or charnockitic to dioritic/noritic intrusions, is the source of aquamarine-topaz-rich pegmatites but mainly of a large dimension stone production. The Late Neoproterozoic–Cambrian Araçuaı´ oro- The most remarkable feature of this crustal gen encompasses the entire region between the segment is the huge amount of different plutonic Saõ Francisco craton and the Atlantic continental igneous rocks of Late Neoproterozoic up to margin, north of latitude 218S, in eastern Brazil Cambro–Ordovician ages, depicting a long lasting (Fig. 1a). Synthesis on the definition, stratigraphy, (c. 630–480 Ma) succession of granite production magmatism, tectonics and evolution of the Araçuaı´ events. Granitic rocks cover one third of the orogenic orogen are found in Pedrosa-Soares & Wiedemann- region, and built up the outstanding Eastern Brazi- Leonardos (2000), Pedrosa-Soares et al. (2001a, lian Pegmatite Province (Fig. 1b) and the most 2007, 2008), De Campos et al. (2004), Silva et al. important dimension stone province of Brazil. This (2005) and Alkmim et al. (2006). is due to the exposure of shallow to deep crustal From:Sial, A. N., Bettencourt, J. S., De Campos,C.P.&Ferreira, V. P. (eds) Granite-Related Ore Deposits. Geological Society, London, Special Publications, 350, 25–51. DOI: 10.1144/SP350.3 0305-8719/11/$15.00 # The Geological Society of London 2011. Downloaded from http://sp.lyellcollection.org/ by guest on April 30, 2019 26 A. C. PEDROSA-SOARES ET AL. Fig. 1. Simplified geological map of the Araçuaı´ orogen and adjacent cratonic region, highlighting the Neoproterozoic and Cambrian granite supersuites (geology modified from Pedrosa-Soares et al. 2008; pegmatite districts modified from Netto et al. 2001 and Pedrosa-Soares et al. 2001b). SFC, Saõ Francisco craton. Location of U–Pb zircon or whole-rock Sm–Nd analysed samples: B, Brasilaˆndia; CC, Carlos Chagas; M, Manhuaçu; MF, Muniz Freire; N, Nanuque; SV, Saõ Vitor. Downloaded from http://sp.lyellcollection.org/ by guest on April 30, 2019 GRANITES AND PEGMATITES, EASTERN BRAZIL 27 levels along an area over 350 000 km2. Therefore, accompanied by delamination and convective those granites record the whole evolutionary removal of lithospheric mantle. The post-collisional history of the Araçuaı´ orogen, from the subduction- stage is related to the climax of the gravitational controlled pre-collisional stage up to the post- collapse of the orogen, which is coeval to astheno- collisional gravitational collapse. sphere ascent. G4 (c. 530–500 Ma) and G5 (c. The authors present the state-of-art of the granite 520–480 Ma) supersuites are post-collisional, and genesis events of the Araçuaı´ orogen and related include plutons that cut and disturb the regional tec- mineral deposits with emphasis on the Eastern tonic trend, as well as concordant bodies intruded Brazilian Pegmatite Province. This information is along structures of distinct ages (Pedrosa-Soares & complemented by new geochemical, geothermo- Wiedemann-Leonardos 2000; De Campos et al. barometric and geochronological data. 2004; Pedrosa-Soares et al. 2001a, 2008). Lateral Based on field relations, structural features, geo- escape of rock masses along major strike–slip chemical and geochronological data, granites from shear zones also took place from the late collisional this orogen were formerly grouped into six suites to post-collisional stages, providing preferred sites (G1, G2, G3S, G3I, G4 and G5) by Pedrosa-Soares for magma emplacement, mainly in the southern & Wiedemann-Leonardos (2000), Pedrosa-Soares region of the Araçuaı´ orogen (De Campos et al. et al. (2001a) and Silva et al. (2005). Additional 2004; Alkmim et al. 2006). data supported a regrouping into five suites (G1 to G5 from De Campos et al. 2004 and Pedrosa-Soares et al. 2008). In the Brazilian geological literature, G1 supersuite the term suite has usually been applied to single batholiths and smaller bodies, as well as to local pet- The following synthesis on G1 supersuite is based on rological associations, named after a confusing data from So¨llner et al. (1991); Nalini-Junior et al. plethora of geographical names. This is the reason (2000a, 2005, 2008); Bilal et al. (2000); Noce why, in this work, we use the designations G1 to et al. (2000, 2006); Pedrosa-Soares & Wiedemann- G5 supersuites, instead of suites and geographical Leonardos (2000); Pedrosa-Soares et al. (2001a, names, to avoid misunderstandings. The grouping 2008); Pinto et al. (2001) ; Whittington et al. of diverse rock units into a supersuite is strictly (2001); Silva et al. (2002, 2005, 2007); De Campos based on petrological and geochemical similarities, et al. (2004); Martins et al. (2004); Vauchez et al. and is constrained by zircon U–Pb ages. Therefore, (2007); Vieira (2007); Gomez (2008); Novo supersuites include suites, batholiths, stocks and (2009); Petitgirard et al. (2009), and references other bodies, which local names will be referred to therein. This supersuite includes suites, batholiths in the following sections. These supersuites can be and stocks locally named Brasilaˆndia, Derribadinha, easily recognized along extensive areas, recording Divino, Estrela-Muniz Freire, Galileía, Guarataia, different evolutionary stages of the Araçuaı´ orogen. Manhuaçu, Mascarenhas-Baixo Guandu, Muriae´, The Brasiliano orogenic event in the Araçuaı´ Saõ Vitor, Teo´filo Otoni, Valentim and others. orogen has been subdivided into four geotectonic The G1 supersuite mainly consists of tonalite to stages (Pedrosa-Soares et al. 2008), namely pre- granodiorite stocks and batholiths, with mafic to collisional (c. 630–585 Ma), syn-collisional (c. diorite facies and autoliths, regionally deformed 585–560 Ma), late collisional (c. 560–530 Ma) during the Brasiliano orogeny but with locally and post-collisional (c. 530–480 Ma). However, in well-preserved magmatic features (Figs 1a & 2). order to better constrain the complexity of the mag- This supersuite also includes metamorphosed matism, protracted transitions, from one geotectonic orthopyroxene-bearing rocks, ranging in compo- stage to another, have been taken into consideration, sition from monzogabbro to quartz monzonite since changes in processes and timing control (Novo 2009). Supracrustal correlatives of the G1 magma genesis. Accordingly, the G1 supersuite is supersuite are metamorphosed pyroclastic and vol- pre-collisional because it represents the building caniclastic rocks of dacite to rhyolite composition of a calc-alkaline magmatic arc, formed in response and volcanic arc signature, dated around 585 Ma to subduction of oceanic lithosphere, from c. 630 to (Vieira 2007). c. 585 Ma. The G2 supersuite is syn-collisional as it Data from almost two hundred samples, from was mainly generated by partial melting of meta- several plutonic and volcanic G1 bodies, outline a sedimentary piles associated with the major crustal predominant medium- to high-K calc-alkaline thickening caused by contractional thrusting and (Fig. 3), metaluminous (Fig. 4), pre-collisional sig- folding, from c. 585 to c. 560 Ma. G3 supersuite nature (Fig. 5), representing a magmatic arc is late collisional to post-collisional (c. 545– formed on an active continental margin setting, 525 Ma). Late collisional refers to the transitional from c. 630 Ma to c. 585 Ma. stage from the waning of convergent forces to the This magmatic arc shows a hybrid isotopic sig- extensional relaxation of the orogen, generally nature, in agreement with Sm–Nd isotope data Downloaded from http://sp.lyellcollection.org/ by guest on April 30, 2019 28 A. C. PEDROSA-SOARES ET AL. Fig. 2. Features of the G1 supersuite: (a) the Manhuaçu tonalite crowded with mafic autoliths, both well-preserved from the regional deformation. (b) stretched mafic enclaves along the regional solid-state foliation of the Galileía suite. (c) mafic autholith partially assimilated by the Galileía tonalite.

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