Timing of anatexis and melt crystallization in the Socorro–Guaxupé Nappe, SE Brazil: Insights from trace element composition of zircon, monazite and garnet coupled to U Pb geochronology

Rocha, Brenda Chung da; Moraes, Renato; Möller, Andreas; Cioffi, Cauê Rodrigues; Jercinovic, Michael J.

doi:10.1016/j.lithos.2016.05.020

Cited by 69 publications

(57 citation statements)

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“…LIN aNd SaWYER reported type of selvedge is also rich in biotite, but occurs as a much wider (up to 10 cm) and compositionally zoned rim between diatexite (melt-rich part) and schollen within it. Mafic schollen are prone to developing this kind of selvedge (Troll & Winter, 1983;Carvalho, Sawyer, & Janasi, 2017; this study), but they also develop around schollen of marble (Figure 1a-d), calcsilicate, pelitic gneiss (Rocha, Moraes, Möller, Cioffi, & Jercinovic, 2017) and residual (Johannes, Ehlers, Kriegsman, & Mengel, 2003) bulk compositions. Troll and Winter (1983) examined the composition of biotite in such a selvedge and attributed its growth to reactions and chemical exchanges between the mafic schollen and surrounding melt-rich diatexite.…”

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confidence: 77%

Microstructure and compositional changes across biotite‐rich reaction selvedges around mafic schollen in a semipelitic diatexite migmatite

Lin

Sawyer

2019

Journal Metamorphic Geology

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Biotite‐rich selvedges developed between mafic schollen and semipelitic diatexite in migmatites at Lac Kénogami in the Grenville Province of Quebec. Mineral equilibria modelling indicates that partial melting occurred in the mid‐crust (4.8–5.8 kbar) in the range 820–850°C. The field relations, petrography, mineral chemistry and whole‐rock composition of selvedges along with their adjacent mafic schollen and host migmatites are documented for the first time. The selvedges measured in the field are relatively uniform in width (~1 cm wide) irrespective of the shape or size of their mafic scholle. In thin section, the petrographic boundary between mafic scholle and selvedge is defined by the appearance of biotite and the boundary between selvedge and diatexite by the change in microstructure for biotite, garnet, plagioclase and quartz. Three subtypes of selvedges are identified according to mineral assemblage and microstructure. Subtype I have orthopyroxene but of different microstructure and Mg# to orthopyroxene in the mafic scholle; subtype II contain garnet with many mineral inclusions, especially of ilmenite, in contrast to garnet in the diatexite host which has few inclusions; subtype III lack orthopyroxene or garnet, but has abundant apatite. Profiles showing the change in plagioclase composition from the mafic schollen across the selvedge and into the diatexite show that each subtype of selvedge has a characteristic pattern. Four types of biotite are identified in the selvedges and host diatexite based on their microstructural characteristics. (a) Residual biotite forms small rounded red‐brown grains, mostly as inclusions in peritectic cordierite and garnet in diatexite; (b) selvedge biotite forms tabular subhedral grains with high respect ratio; (c) diatexite biotite forms tabular subhedral grains common in the matrix of the diatexite; and (d) retrograde biotite that partially replaces peritectic cordierite and garnet in the diatexite. The four groups of biotite are also discriminated by their major element (EMPA) and trace elements (LA‐Q‐ICP‐MS) compositions. Residual biotite is high in TiO2 and low in Sc and S, whereas retrograde biotite has high Al2O3, but low Sc and Cr. Selvedge and diatexite biotite are generally very similar, but selvedge biotite has higher Sc and S contents. Whole‐rock compositional profiles across the selvedges constructed from micro‐XRF and LA‐Q‐ICP‐MS analyses show: (a) Al2O3, FeO, MgO and CaO all decrease from mafic scholle across the selvedge and into the diatexite; (b) Na2O is lowest in the mafic scholle, rises through the selvedge and reaches its maximum about 20–30 mm into the diatexite host; (c) K2O is lowest in the mafic scholle and reaches its highest value in the first half of the selvedge, then declines before reaching a higher, but intermediate value, about 20 mm into the diatexite. Of the trace elements, Cs and Rb show distributions very similar to K2O.

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confidence: 77%

Microstructure and compositional changes across biotite‐rich reaction selvedges around mafic schollen in a semipelitic diatexite migmatite

Lin

Sawyer

2019

Journal Metamorphic Geology

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“…In southern Minas Gerais, Brazil, the base of the Metatexite Unit of the Socorro-Guaxupé Nappe is an excellent example of diatexite with voluminous leucosome and abundant fragment of schollen, either of its residue or mafic granulite, locally with layers of transitional stromatic migmatite. One of the best outcrops of this unit occurs in an inactive quarry on the road between Alfenas and Machado, from where a complex history was recently revealed by a petrochronology study using zircon and monazite ages and chemistry (Rocha et al 2017). As the rock is composed of more than 50% of leucosome, including undeformed to deformed types, bearing garnet and orthopyroxene, and with large variation in bulk composition, it represents an ideal laboratory to evaluate whether the processes of partial melting, segregation and crystallization occurred in an open or closed system and what was the role of deformation in it.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the contributions of possible sources to the leucosome of the diatexite of Socorro-Guaxupé Nappe, in the Alfenas Region, MG, Brazil

Tasco

Moraes

2019

Braz. J. Geol.

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The Socorro-Guaxupé Nappe crops out in southern Minas Gerais and it has an intermediate unit called Metaxite Unit, dominated by diatexites at its base, with large volumes of leucosome and schollen of stromatic garnet-biotite metatexite. Leucosome within the schollen crystallized via fractional crystallization and is dominated by plagioclase and quartz, although K-feldspar might be present. However, the larger volume of the coarse-grained leucosome, that dominates the unit, has granite, sometimes close to minimum granite composition. So, its formation, after partial melting, involved, segregation, fractional crystallization and accumulation. Proportions of leucosome / residue and leucosome / residue / peritectic phases indicate that the leucosome crystallized from more melt than a pelite source could produce, and probably diatexite worked as a pre-magmatic chamber and stocked melt produced from the granulites sitting at its bottom. Large proportion of biotite crystallized in the residue was formed due to equalization of water chemical potential between residue and leucosome.The Brasilia Orogen has been interpreted as the result of the neoproterozoic collision between the passive margin of the São Francisco and the active margin of the Paranapanema Evaluation of the contributions of possible sources to the leucosome of the diatexite of Socorro-Guaxupé Nappe, in the Alfenas Region, MG, Brazil Figure 10. Proportions of the migmatite parts recognized in field and normalized to 100%; peritectic garnet (Grt), leucosome (Leu) and schollen -residue (Rsd).

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“…An interval in ages like this one was recognized in the metamorphic-partial meltingcrystallization evolution of the root of a magmatic arc in the Southern Brasilia Belt (Rocha et al, 2017), on the West boundary of the Ribeira Belt.…”

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confidence: 76%

Modelagem termodinâmica de fusão parcial e metamorfismo em condições de fácies granulito: exemplo do complexo Itatins, SP

Silva¹

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AgradecimentosEm primeiro lugar gostaria de agradecer à Cíntia por todo o apoio durante esses anos, sempre me incentivando, especialmente nos momentos mais difíceis.Agradeço a meus pais, Francisco e Sônia pelo apoio nessa empreitada.Ao amigo e orientador Renato de Moraes, por ter aceitado me orientar nesse projeto que começou com a partir de duas amostras de "presente".Ao colega de CPRM e Prof. Frederico Meira Faleiros, pela disposição demonstrada da busca por uma área alvo de estudo, por me apresentar a região de Peruíbe e pela ajuda na fase final do projeto.Aos amigos Bruna, Renato e Darwin, por terem se tornado parte da nossa família.Aos Professores Adriana Alves, Rogério Guitarrari Azzone, Gergely Szabó, Lucelene Martins, SilvioFarias Vlach e aos colegas da pós-graduação pela ajuda e discussão de assuntos petrológicos;Ao pessoal da gráfica, em especial Henrique e Claudionor sempre solícitos para ajudar com as cópias dos trabalhos e apostilas;Aos funcionários do instituto, entre eles Katerine e Alexandre da Seção de Pós-graduação, Marcos e Leandro (microssonda) Angélica (petrografia), Isaac (MEV), Valter, Solange e Luiza (CPGEO) e ao pessoal do laboratório de química e da laminação.À equipe do laboratório de microssonda electrônica da UFRGS, Prof. Dra. Márcia Gomes e Susan.Aos amigos que sempre estiveram presentes: André, Elder, Graziani, Gustavo, Fábio, Felipe, Júlio, Leopoldo e Rafael, Camila e Maria Elisa.Gostaria de agradecer a todos os meus colegas e superiores da CPRM -Serviço Geológico do Brasil, pois o meu doutorado e minha ida ao Canadá só foram possíveis devido à colaboração e à confiança de todos. Dentre esses faço um agradecimento especial aos colegas da Gerência de Geologia e Recursos Minerais (GEREMI) da Superintendência Regional de São Paulo (SUREG-SP), Elizete Domingues Salvador, José Carlos Garcia Ferreira (Diretor de Geologia e Recursos Minerais), Dr. Luiz Carlos da Silva e Dr. Roberto Ventura dos Santos (ex-Diretor de Geologia e Recursos Minerais) e ao Dr. Manoel Barretto (ex-diretor presidente).Agradeço também a toda equipe do Grupo de Pesquisa em Recursos Minerais da Université du Quebec à Chicoutimi (Canadá), em especial Charley Duran, Luiz Salim, Marko Prasek, Nadège Samalens e Pia Plese.Aos Professores Dr. Edward W. Sawyer e Dra. Sarah-Jane Barnes, cuja dedicação à pesquisa, generosidade e confiança em meu trabalho permitiu um grande avanço em meu conhecimento científico. RESUMONo presente trabalho são apresentados os resultados da modelagem da fusão parcial a partir de composições químicas ideais de grauvaca, folhelho e granodiorito visando estabelecer uma metodologia para o estudo de rochas da fácies granulito submetidas à fusão parcial usando o programa THERMOCALC. Os resultados são comparados à rochas ortoderivadas do Complexo Itatins, Faixa Ribeira Meridional, SP. O complexo está localizado na junção dos terrenos tectono-estratigráficos Embu, Curitiba e Costeiro e é constituído por dois tipos principais de rochas: (i) biotita granulito félsico e (ii) paragnaisse migmatítico estro...

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Timing of anatexis and melt crystallization in the Socorro–Guaxupé Nappe, SE Brazil: Insights from trace element composition of zircon, monazite and garnet coupled to U Pb geochronology

Cited by 69 publications

References 73 publications

Microstructure and compositional changes across biotite‐rich reaction selvedges around mafic schollen in a semipelitic diatexite migmatite

Microstructure and compositional changes across biotite‐rich reaction selvedges around mafic schollen in a semipelitic diatexite migmatite

Evaluation of the contributions of possible sources to the leucosome of the diatexite of Socorro-Guaxupé Nappe, in the Alfenas Region, MG, Brazil

Modelagem termodinâmica de fusão parcial e metamorfismo em condições de fácies granulito: exemplo do complexo Itatins, SP

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