Browsing by Author "Farina, Federico"
Now showing 1 - 7 of 7
Results Per Page
Sort Options
Item Archean evolution of the southern São Francisco craton (SE Brazil).(2017) Albert, Capucine; Lana, Cristiano de Carvalho; Farina, Federico; Lana, Cristiano de Carvalho; Gerdes, Axel; Storey, Craig Darryl; Cipriano, Ricardo Augusto Scholz; Pimentel, Márcio MartinsOs continentes modernos são fundamentalmente diferentes de suas contrapartes Arqueanas, devido à influência de um manto substancialmente mais quente sobre a produção e as propriedades reológicas da crosta no início da Terra. Particularmente, a natureza e a composição do registro de rochas ígneas sofreram modificações significativas no final do eon Arqueano, atestando mudanças importantes nos processos geodinâmicos. Este trabalho concentra-se nas rochas granitóides posicionadas na porção sul do craton São Francisco no sudeste do Brasil. Uma combinação de observações de campo e petrográficas, geoquímica de rocha total e análises de isotópicas (U-Pb, Lu- Hf, O e B) foram realizadas para um melhor entendimento nos mecanismos que levaram à formação e estabilização deste bloco cratônico, além de compreender as modificações geodinâmicas globais ocorridas durante esse período. O embasamento do Quadrilátero Ferrífero, no sul do cráton São Francisco, consiste em ortognaisses, intrudidos por abundantes plútons granitóides e associados produtos magmáticos (veios pegmatíticos/aplíticos, por exemplo). O embasamento do Quadrilátero Ferrífero registra três períodos principais de magmatismo, denominados de Rio das Velhas I (RVI) e II (RVII) de 2.92-2.85 e 2.80-2.76 Ga, respectivamente, e o último evento Mamona (2.75-2.68 Ga). Granitóides e gnaissses dos três complexos do embasamento estudados (Bação, Belo Horizonte e Bonfim) foram subdivididos em dois grupos, refletindo diferentes processos petrogenéticos e/ou fontes: rochas de médio- e alto-K. Os gnaisses e granitóides de médio-K foram formados durante os eventos Rio das Velhas I e II. Essas rochas apresentam algumas semelhanças com os TTG Arqueanos, apesar de possuírem um pequeno enriquecimento em SiO2 e K2O e depleção em Al2O3, e foram interpretadas como o resultado da mistura entre um membro final derivado da fusão parcial de uma rocha metabasáltica e um fundido resultante da reciclagem de uma crosta mais antiga de composição TTG. Por outro lado, os granitos de alto-K colocados na crosta durante subsequente evento Mamona, assemelham-se aos típicos granitóides à biotita do Arqueano tardio, com origem interpretada da fusão parcial de metassedimentos imaturos. O envolvimento de metassedimentos na petrogênese destes magmas de alto-K Neoarqueanos é ainda suportado por: (i) uma tendência para valores pesados de δ18O(Zrc), indicando equilíbrio isótopico de O em condições de subsuperfície, e (ii) a presença fundidos magmáticos ricos em boro e fluídos intrudidos em 2.70-2.60 Ga, provavelmente derivados de um protólito metassedimentar rico em boro. Em geral, propomos que a evolução magmática e geodinâmica da porção sul do craton São Francisco ocorreu da seguinte maneira. De ~ 3.50 a 2.90 Ga, fragmentos de crosta juvenil (possivelmente TTGs) foram produzidos, formando o protólito do atual sul do cráton São Francisco. Este é um período de crescimento crustal, como evidenciado pela modelagem isotópica de hafnium à partir de zircões detríticos. Em ~ 2.90 Ga, a crosta sofreu significativas modificações, devido ao início de uma tectônica colisional. Diversos fragmentos crustais com histórias distintas foram acrescidos progressivamente, construindo, por fim, um núcleo continental rígido e soerguido. Isto é suportado por: (i) a transição para um regime dominado por reciclagem crustal, com diminuição de contribuição mantélica em magmas recém-gerados, (ii) o envolvimento de componentes TTG mais antigos na geração de magmas de médio-K durante os eventos RVI e RVII e a simultânea ausência de materiais crustais preservados mais velhos que ~ 2.90 Ga na porção sul do craton São Francisco, (iii) a abundância de sistemas hidrotermais na porção superior da crosta evidenciados por valores leves de δ18O(Zrc), indicando o soerguimento de grandes porções da crosta continental durante o Neoarqueano, (iv) a progressiva maturação crustal, registrada por uma tendência para o magmatismo mais potássico e rico em HFSE (High Field Strength Element). O soerguimento e rápido soterramento de grandes bacias sedimentares dominadas por componentes clásticos no Neoarqueano (~ 2.75 Ga) levaram à produção de granitóides de alto-K durante o evento Mamona. Fluidos magmáticos diferenciados portadores de turmalina percolaram a crosta e interagiram de forma generalizada com o greenstone belt adjacente. A presença de turmalina hidrotermal de origem magmática (e Neoarqueana) em associação espacial próxima aos complexos do embasamento sugere que a formação das estruturas domo e quilhas ocorreu antes do último evento magmático (ou seja, antes de 2.70 Ga), o que está em desacordo com a idéia de que a região adquiriu sua arquitetura atual durante o Paleoproterozóico.Item Genesis and evolution of a neoproterozoic magmatic arc : the cordilleran-type granitoids of the Araçuaí Belt, Brazil.(2018) Narduzzi, Francesco; Nalini Júnior, Hermínio Arias; Farina, Federico; Lana, Cristiano de Carvalho; Stevens, Gary; Nalini Júnior, Hermínio Arias; Tohver, Eric; Heilbron, Monica da Costa Pereira Lavalle; Queiroga, Gláucia Nascimento; Cipriano, Ricardo Augusto ScholzThe Araçuaí orogen (SE Brazil) is one of the largest (350,000 km2 ) and long-lived (ca. 630 – 480 Ma) granitic province in the world. The peculiarity of this Orogen is its wide variety of granitoids recording mid- to lower crustal P - T conditions that allow direct investigation of petrological processes occurring in the deepest part of the continental crust. This study investigates the field, textural, geochemical, geochronological and isotopic evolution of the pre-collisional Galiléia Batholith outcropping in the central part of the Araçuaí orogen. This metaluminous to slightly metaluminous (ASI = 0.97– 1.07) batholith, is a large is (ca. 15,000 km2 ), Neoproterozoic (ca. 632–550 Ma) weakly foliated, calc-alkaline, granitoid body characterized by the widespread occurrence of grossular-rich magmatic garnet and magmatic epidote. This is a rare mineral association in Cordilleran-I-type granitoids and of special petrogenetic significance. Field, petrographic, and mineral chemistry evidence indicate that garnet, epidote, biotite as well as white mica crystals (low-Si phengite), are magmatic. There is no difference in bulk rock major and trace element composition between the Galiléia and other garnetfree cordilleran-type granitoids worldwide. Thus the uncommon garnet+epidote parageneses are related to the conditions of magma crystallization, such as pressure, temperature and water content. Comparison between the mineral assemblages and mineral compositions from this study and those recorded in crystallization experiments on metaluminous calc-alkaline magmas, as well as within garnet-bearing metaluminous volcanic rocks and granitoids, indicates that the supersolidus coexistence of grossularrich garnet, epidote and white mica is consistent with magma crystallization at pressures greater than 0.8 GPa (above 25 km depth). This indicates that the Galiléia batholith was assembled in the lower crust during the accretionary/collisional stages of the Neoproterozoic Brasiliano Orogeny. It is evident that this granitic body represents a natural laboratory for studying the history of a lower crustal magma reservoir. Indeed the lifetime of deep magma chambers and the duration of magmatic activity in them remains a puzzle, contrary to young upper crustal magmatic systems. Despite being homogeneous with respect to mineralogy/texture and major/trace elements, all samples from the central part of the batholith record extreme variability in U-Pb magmatic ages from ca. 630 to 555 Ma. Trace element geochemistry and Hf isotopes from the igneous zircons – here interpreted as autocrysts (ca. 555 – 560 Ma) and antecrysts (> 560 Ma) – are all consistent with an open-system crystallization, rather than a simple cooling following fractional crystallization at the level of magma emplacement. We interpret the age variability recorded by the Galiléia samples as the result of a long-lived, uninterrupted injection of magmas of similar composition during assembly of the batholith. Such continuous injections of magma took place in the lower crust, keeping the system above its solidus through the 80 Ma of zircon crystallization. Unradiogenic 176Hf/177Hf and 143Nd/144Nd isotopic values of the Galileía samples indicate no direct mixing with mantle-derived magmas during the assembly and growth of the Galiléia batholith. This explains the scarcity of mafic products in the region. All of these characteristics need a more suitable geodynamic scenario. Indeed mineral textural, geochronological and isotopic similarities with other younger and older granitic plutons constructed within accretionary / fore-arc settings, better explain the characteristics showed by the Galiléia granitoids. Thus it is suggested that this giant batholith was assembled in an accretionary prism during the Brasiliano Orogenic stages. Eventually, it is likely that during the Brasiliano/Pan-African orogeny, accretionary prism, fore- and back–arc setting were sites of voluminous silicic magmatism and commonplaces for the stabilization of continental crust and its differentiation.Item Magmatic garnet in the Cordilleran-type Galiléia granitoids of the Araçuaí belt, Brazil : evidence for crystallization in the lower crust.(2017) Narduzzi, Francesco; Farina, Federico; Stevens, Gary; Lana, Cristiano de Carvalho; Nalini Júnior, Hermínio AriasMagmatic garnet, together with epidote, is a rare mineral association in cordilleran-I-type granitoids and of special petrogenetic significance. The metaluminous to slightly peraluminous (ASI = 0.97–1.07) Galiléia batholith (Brazil) is a large (ca. 30,000 km2), Neoproterozoic (ca. 632–570 Ma) weakly foliated calc-alkaline granitoid body, characterized by the widespread occurrence of garnet (grossular 25–43 mol%) and epidote (pistacite 9.3–22.7 mol%). Field, petrographic and mineral chemical evidence indicates that garnet, epidote, biotite as well as white mica crystals (low-Si phengite), are magmatic. There is no difference in bulk rock major and trace element composition between the Galiléia granitoids and other garnet-free cordilleran-type granitoids worldwide. This evidence strongly suggests that the origin of the uncommon garnet+epidote parageneses is related to the conditions of magma crystallization, such as pressure, temperature and water content. Comparison between the mineral assemblages andmineral compositions fromthis study and those recorded in crystallization experiments on metaluminous calc-alkaline magmas, as well as within garnet-bearing metaluminous volcanic rocks and granitoids, indicates that the supersolidus coexistence of grossular-rich garnet, epidote and white mica is consistentwith magma crystallization at pressures greater than 0.8 GPa (above 25 km depth) and at temperatures below 700 °C, i.e. near the water saturated solidus. Furthermore, resorption textures around garnet (plagioclase ± quartz coronas) and epidote suggest that these minerals have been partially consumed prior to complete crystallization. These findings demonstrate that at 630 Ma the crust underneath the Araçuaí Orogen was already at least 25–30 km thick and relatively cool. However, this contrasts with the marked high heat flow registered from the neighbour Carlos Chagas Batholith located 50 km to the east. In fact such granitoids record granulite-facies metamorphism at the same pressure and time (ca. 570 Ma) of Galiléia granitoids crystallization. Thus, a more suitable geodynamic scenario is required in order to explain these two contrasting thermal regimes within the same orogen. Eventually, field, petrographic and mineral chemical analogies with similar garnet-bearing granitoids located in the fore-arc settings of the British Columbia subduction zone, possibly imply that the Galiléia granitoids represent “rare” garnet- and epidote-bearing metaluminous Cordilleran-Itype granites which can only form in a fore-arc setting.Item Metamorphism and exhumation of basement gneiss domes in the Quadrilátero Ferrífero : two stage dome-and-keel evolution?(2019) Cutts, Kathryn Ann; Lana, Cristiano de Carvalho; Alkmim, Fernando Flecha de; Farina, Federico; Moreira, Hugo Souza; Coelho, Viviane VianaThe presence of dome-and-keel provinces in Archean cratons has been connected with the initiation of plate tectonics on Earth as these features are most commonly observed in Archean rocks. The Quadrilátero Ferrífero in Brazil has been identified as a Paleoproterozoic dome-and-keel province for more than three decades. The prevailing model suggests that it formed during the Rhyacian Transamazonian orogeny, making it unique among dome-and-keel provinces. However, a lack of appropriate lithologies, datable minerals and the metamorphic overprint of later orogenesis has resulted in a cryptic metamorphic record for the formation of this dome-and-keel province. A clinopyroxene-bearing migmatite from the core of the Bação dome has peak PeT conditions of 5e7 kbar and 700e750 C and a published age of ca. 2730 Ma based on UePb ages of zircon from leucosomes, suggesting that this age represents the migmatisation event. A fine-grained epidote-albite-titanite assemblage overprints the coarse-grained clinopyroxene and amphibole, giving PeT conditions of 8e9 kbar and 550 C with an associated titanite age of ca. 2050 Ma. A garnet-bearing amphibolite sample also from the core of the dome has peak PeT conditions of 7e8 kbar and 650e700 C, and texturally late titanite from this sample produces an age of ca. 2060 Ma. Three additional samples were collected from the edges of the dome. A garnet-gedrite bearing felsic schist produces peak PeT conditions of 8e9 kbar and 650e700 C on a clockwise PeT evolution. This sample has a UePb zircon age of ca. 2775 Ma, which could date metamorphism or be the age of its volcaniclastic protolith. Texturally unconstrained titanite from the sample gives an age of ca. 2040 Ma. A garnet-bearing amphibolite that occurs as a boudin within the felsic schist gives both zircon and titanite ages of ca. 2050 Ma and has peak PeT conditions of 5e6 kbar and 650e700 C on a near isobaric PeT path. An amphibolite dike, observed to cross-cut the felsic schist produces a zircon UePb age of ca. 2760 Ma. Altogether this data suggests that the samples were metamorphosed in the Archean (ca. 2775e2730 Ma) and again during the Transamazonian event. The most plausible explanation for this data is that dome-and-keel formation occurred in the Archean with migmatisation and high-temperature metamorphism occurring at this time. The Paleoproterozoic event is interpreted as a reactivation of the dome-and-keel formation structures, with Paleoproterozoic keels crosscutting Archean keels and producing metamorphic aureoles. The high radiogenic heat production and the presence of dense sedimentary successions in Archean terranes make dome-and-keel provinces a uniquely Archean feature, but they are susceptible to reworking, resulting in an enigmatic record of formation.Item New U-Pb ages and lithochemical attributes of the Ediacaran Rio Doce magmatic arc, Araçuaí confined orogen, southeastern Brazil.(2014) Gonçalves, Leonardo Eustáquio da Silva; Farina, Federico; Lana, Cristiano de Carvalho; Soares, Antônio Carlos Pedrosa; Alkmim, Fernando Flecha de; Nalini Júnior, Hermínio AriasThe Araçuaí orogen of southeastern Brazil, together with its counterpart located in Africa, the West Congo belt, formed through closure of a gulf connected to the Adamastor Ocean by the end of the Ediacaran and beginning of the Cambrian. Convergence of the margins of the gulf led to the development of the Rio Doce magmatic arc between 630 Ma and 580 Ma on a continental basement mostly composed of Rhyacian orthogneisses. The Rio Doce arc mainly consists of tonalite-granodiorite batholiths, generally crowded with mafic to dioritic enclaves, and minor gabbronorite-enderbite-charnockite plutons, suggesting mixing processes involving crustal and mantle sources. We investigate the basement, magma sources and emplacement ages of the Rio Doce arc. Our data suggest the arc comprises three main granitic rock groups: i) Opx-bearing rocks mostly of enderbite to charnockite composition; ii) enclaverich tonalite-granodiorite (ETG); and iii) enclave-poor granite-granodiorite with minor tonalite (GT). The Opx-bearing rocks are magnesian, calc-alkalic to alkali-calcic and metaluminous. Together, the ETG and GT rock groups range in composition from tonalite to granite, are metaluminous to slightly peraluminous, show a predominantly medium- to high-K, expanded calc-alkaline signature, and other geochemical and isotopic attributes typical of a pre-collisional volcanic arc formed on a continental margin setting. Mineralogical, chemical, and geochronological data suggest the involvement of HTmelting of granulitic (H2O-depleted) sources of Rhyacian age for the generation of Opx-bearing granitic rocks, additionally to magma mixing and fractional crystallization processes. In conclusion, the studied rock groups of the Rio Doce arc were likely formed by interactions of mantle and crustal processes, in an active continental margin setting. These processes involved ascent of mantle magmas that induced partial melting on the continental basement represented by the Rhyacian gneisses.Item Palaeoproterozoic assembly of the São Francisco craton, SE Brazil : new insights from U–Pb titanite and monazite dating.(2017) Aguilar, Carmen; Alkmim, Fernando Flecha de; Lana, Cristiano de Carvalho; Farina, FedericoIsotopic U–Pb titanite and monazite data from the southern São Francisco craton better constrain the timing of the tectono-thermal event that led to the amalgamation of the craton and the crust that forms the basement of its fringing orogenic belts in the Palaeoproteroic. The data obtained from assemblages exposed in the Quadrilátero Ferrífero mining district and adjacent Palaeoproterozoic Mineiro belt magmatic arc terrane reveal two different age populations: a first metamorphic event between 2772 and 2613 Ma, followed by recrystallization or/and isotopic resetting in the interval of 2080–1940 Ma. The partial preservation of Neoarchaean ages in the craton interior suggests that the Palaeoproterozoic metamorphism did not exceed the minimum closure temperature for the titanite (between 650 C and 700 C), which is also reinforced by the absence of Palaeoproterozoic metamorphic zircons in the southern São Francisco craton. Combining new and existing Palaeoproterozoic data, we infer that the Archaean crust of the southern craton as well as the surrounding magmatic arcs were affected by a long-lived metamorphic event from ca. 2100 Ma to 1940 Ma. These age interval includes an episode of syn-collisional metamorphism between 2100 and 2070 Ma, which represents the amalgamation of the Archaean nuclei of both the São Francisco and Congo cratons, along with magmatic arcs and microcontinents. This collision led to closure of the large Palaeoproterozoic Minas basin, followed by orogenic collapse and development of a dome-and-keel architecture in time interval of 2070–2050 Ma. A period of slow cooling ( 1 C/Ma) succeeded these events and lasted until ca. 1940 Ma. Our results correlate with the Palaeoproterozoic metamorphic ages obtained in the various blocks forming the northeastern sector of the craton.Item The Archeane-Paleoproterozoic evolution of the Quadrilátero Ferrífero, Brasil : current models and open questions.(2016) Farina, Federico; Albert, Capucine; Martinez Dopico, Carmen Irene; Gil, Carmen Maria Aguilar; Moreira, Hugo Souza; Hippertt, J. P.; Cutts, Kathryn Ann; Alkmim, Fernando Flecha de; Lana, Cristiano de CarvalhoThe Quadril atero Ferrífero is a metallogenic district (Au, Fe, Mn) located at the southernmost end of the S~ao Francisco craton in eastern Brazil. In this region, a supracrustal assemblage composed of Archean greenstone and overlying NeoarcheanePaleoproterozoic sedimentary rocks occur in elongated keels bordering domal bodies of Archean gneisses and granites. The tectonomagmatic evolution of the Quadril atero Ferrífero began in the Paleoarchean with the formation of continental crust between 3500 and 3200 Ma. Although this crust is today poorly preserved, its existence is attested to by the occurrence of detrital zircon crystals with Paleoarchean age in the supracrustal rocks. Most of the crystalline basement, which is composed of banded gneisses intruded by leucogranitic dikes and weakly foliated granites, formed during three major magmatic events: Rio das Velhas I (2920e2850 Ma), Rio das Velhas II (2800e2760 Ma) and Mamona (2760e2680 Ma). The Rio das Velhas II and Mamona events represent a subduction-collision cycle, probably marking the appearance of a modern-style plate tectonic regime in the Quadril atero Ferrífero. Granitic rocks emplaced during the Rio das Velhas I and II events formed by mixing between a magma generated by partial melting of metamafic rocks with an end member derived by recycling gneissic rocks of older continental crust. After deformation and regional metamorphism at ca. 2770 Ma, a change in the composition of the granitic magmas occurred and large volumes of high-K granitoids were generated. The ca. 6000 m-thick Minas Supergroup tracks the opening and closure of a basin during the NeoarcheanePaleoproterozoic, between 2600 and 2000 Ma. The basal sequence involves continental to marine sediments deposited in a passive margin basin and contain as a marker bed the Lake Superiortype Cau^e Banded Iron Formation. The overlying sediments of the Sabar a Group mark the inversion of the basin during the Rhyacian Minas accretionary orogeny. This orogeny results from the collision between the nuclei of the present-day S~ao Francisco and Congo cratons, generated the fold-and thrust belt structure of the Quadril atero Ferrífero. Afterwards, the post- orogenic collapse resulted in the deposition of the Itacolomi Group and in the genesis of the dome-and-keel structure. In this paper, we review current knowledge about the 1500 Ma long-lasting tectonomagmatic and structural evolution of the Quadril atero Ferrífero identifying the most compelling open questions and future challenges.