Petrological implications of melanite in the rocks of the Morro de São João Alkaline Complex, Casimiro de Abreu, Rio de Janeiro, Brazil
Abstract This article presents a study of the titanium-rich andradite garnet, melanite, which occurs in the rocks of the Morro de São João Alkaline Complex, of Paleocene age, located in the district of Casimiro de Abreu, southeast of the state of Rio de Janeiro, Brazil. The complex comprises felsic...
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Sociedade Brasileira de Geologia
2025-01-01
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| Series: | Brazilian Journal of Geology |
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| author | Mariana Bessa Fagundes Anderson Santos Mauro Geraldes Sérgio de Castro Valente Eliane Guedes Theresa Rocco Pereira Barbosa Júlio Lopes |
| author_facet | Mariana Bessa Fagundes Anderson Santos Mauro Geraldes Sérgio de Castro Valente Eliane Guedes Theresa Rocco Pereira Barbosa Júlio Lopes |
| author_sort | Mariana Bessa Fagundes |
| collection | DOAJ |
| description | Abstract This article presents a study of the titanium-rich andradite garnet, melanite, which occurs in the rocks of the Morro de São João Alkaline Complex, of Paleocene age, located in the district of Casimiro de Abreu, southeast of the state of Rio de Janeiro, Brazil. The complex comprises felsic to mafic syenitic rocks associated with pseudoleucite. The garnet-bearing rocks are composed of a mineralogical assemblage rich in Ti and Ca, consisting mainly of alkali-feldspar, nepheline, clinopyroxene and amphiboles rich in calcium, and accessory phases containing titanite, titanite-rich magnetite, apatite, annite, and melanite. This mineral has contents of up to 4.91 wt.% TiO2, and its molecular constituents include andradite (73.54%), grossular (17.09%), and hutcheonite (9.34%). The presence of melanite, mainly associated with calcium clinopyroxene, indicates a crystallization environment characterized by conditions of high oxygen fugacity and the influence of mantle metasomatism at its source. Furthermore, as this garnet is the result of late crystallization, its presence indicates that the bearing rocks, even the most parental ones, are evolved rocks, given the low contents of MgO (< 8.14 wt.%) and Ni (< 60 ppm), as opposed to the high levels of Ba (< 10,840 ppm), Rb (< 464 ppm), and Sr (< 10,000 ppm). |
| format | Article |
| id | doaj-art-b534f9b6299d466a9a0335fd1670ec02 |
| institution | Kabale University |
| issn | 2317-4692 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | Sociedade Brasileira de Geologia |
| record_format | Article |
| series | Brazilian Journal of Geology |
| spelling | doaj-art-b534f9b6299d466a9a0335fd1670ec022025-01-14T07:39:15ZengSociedade Brasileira de GeologiaBrazilian Journal of Geology2317-46922025-01-0154310.1590/2317-4889202420240016Petrological implications of melanite in the rocks of the Morro de São João Alkaline Complex, Casimiro de Abreu, Rio de Janeiro, BrazilMariana Bessa Fagundeshttps://orcid.org/0000-0002-6796-0626Anderson Santoshttps://orcid.org/0000-0003-2526-8620Mauro Geraldeshttps://orcid.org/0000-0003-2914-2814Sérgio de Castro Valentehttps://orcid.org/0000-0002-7467-672XEliane Guedeshttps://orcid.org/0000-0001-6785-7584Theresa Rocco Pereira Barbosahttps://orcid.org/0009-0001-2789-9226Júlio Lopeshttps://orcid.org/0000-0001-6230-0058Abstract This article presents a study of the titanium-rich andradite garnet, melanite, which occurs in the rocks of the Morro de São João Alkaline Complex, of Paleocene age, located in the district of Casimiro de Abreu, southeast of the state of Rio de Janeiro, Brazil. The complex comprises felsic to mafic syenitic rocks associated with pseudoleucite. The garnet-bearing rocks are composed of a mineralogical assemblage rich in Ti and Ca, consisting mainly of alkali-feldspar, nepheline, clinopyroxene and amphiboles rich in calcium, and accessory phases containing titanite, titanite-rich magnetite, apatite, annite, and melanite. This mineral has contents of up to 4.91 wt.% TiO2, and its molecular constituents include andradite (73.54%), grossular (17.09%), and hutcheonite (9.34%). The presence of melanite, mainly associated with calcium clinopyroxene, indicates a crystallization environment characterized by conditions of high oxygen fugacity and the influence of mantle metasomatism at its source. Furthermore, as this garnet is the result of late crystallization, its presence indicates that the bearing rocks, even the most parental ones, are evolved rocks, given the low contents of MgO (< 8.14 wt.%) and Ni (< 60 ppm), as opposed to the high levels of Ba (< 10,840 ppm), Rb (< 464 ppm), and Sr (< 10,000 ppm).http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892024000300300&lng=en&tlng=enalkaline magmatismmelanitetitanium-rich andraditecompositional zoningdisequilibrium texturesoxygen fugacitymantle metasomatismcrustal assimilation |
| spellingShingle | Mariana Bessa Fagundes Anderson Santos Mauro Geraldes Sérgio de Castro Valente Eliane Guedes Theresa Rocco Pereira Barbosa Júlio Lopes Petrological implications of melanite in the rocks of the Morro de São João Alkaline Complex, Casimiro de Abreu, Rio de Janeiro, Brazil Brazilian Journal of Geology alkaline magmatism melanite titanium-rich andradite compositional zoning disequilibrium textures oxygen fugacity mantle metasomatism crustal assimilation |
| title | Petrological implications of melanite in the rocks of the Morro de São João Alkaline Complex, Casimiro de Abreu, Rio de Janeiro, Brazil |
| title_full | Petrological implications of melanite in the rocks of the Morro de São João Alkaline Complex, Casimiro de Abreu, Rio de Janeiro, Brazil |
| title_fullStr | Petrological implications of melanite in the rocks of the Morro de São João Alkaline Complex, Casimiro de Abreu, Rio de Janeiro, Brazil |
| title_full_unstemmed | Petrological implications of melanite in the rocks of the Morro de São João Alkaline Complex, Casimiro de Abreu, Rio de Janeiro, Brazil |
| title_short | Petrological implications of melanite in the rocks of the Morro de São João Alkaline Complex, Casimiro de Abreu, Rio de Janeiro, Brazil |
| title_sort | petrological implications of melanite in the rocks of the morro de sao joao alkaline complex casimiro de abreu rio de janeiro brazil |
| topic | alkaline magmatism melanite titanium-rich andradite compositional zoning disequilibrium textures oxygen fugacity mantle metasomatism crustal assimilation |
| url | http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892024000300300&lng=en&tlng=en |
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