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| Formato: | Artículo científico |
| Lenguaje: | en |
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Academia Brasileira de Ciências
2001
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| Acceso en línea: | https://www.redalyc.org/articulo.oa?id=32773108 |
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| author | Gianbosco Traversa |
| author_facet | Gianbosco Traversa |
| contents | Petrography and mineral chemistry of carbonatites and mica-rich rocks from the Araxá complex (Alto Paranaíba Province, Brazil) Gianbosco Traversa Celso B. Gomes Piero Brotzu Nicoletta Buraglini Lucio Morbidelli Maria Speranza Principato Sara Ronca Excelso Ruberti Multidisciplinaria (Ciencias Naturales y Exactas) carbonatites geochemistry alkaline rocks The Araxá complex (16 km2) comprises carbonatites forming a central core and a complex network ofconcentric and radial dykes as well as small veins; additionally, it includes mica-rich rocks, phoscorites andlamprophyres. Fenites also occur and are represented by Proterozoic quartzites and schists of the AraxáGroup.The petrographic study of 130 borehole samples indicates that the complex is basically made up by tworock-types, carbonatites and mica-rich rocks, and subordinately by a third unit of hybrid composition.Carbonatites range chemically in composition, the most abundant type being magnesiocarbonatites. Dolomiteand calcite correspond to the chief constituents, but other carbonate phases, including the Ce-group REminerals, are also recognized. Phosphates and oxides are widespread accessories whereas silicate mineralsconsist of olivine, clinopyroxene, mica and amphibole.Mica-rich rocks are represented by abundant glimmeritic rocks and scarce cumulitic phlogopite-, olivine- anddiopside-bearing pyroxenites. Hybrid rocks mainly contain phlogopite and tetraferriphlogopite as cumulusand intercumulus phases, respectively; carbonate minerals may also be found.Chemical data indicate that the carbonatites are strongly enriched in REE and have lower contents of Nb, Zr,V, Cr, Ni and Rb compared to the mica-rich rocks. The higher K, Nb and Zr contents of the latter rocks arebelieved to be related to metasomatic processes (glimmeritization) of the pyroxenites.Similar REE patterns for carbonatites and mica-rich rocks seem to suggest that they are related to a singleparental magma, possibly of ijolitic composition. Steep LREE/HREE fractionation and high REE contentof some carbonatite samples would be explained by hydrothermal and supergenic processes. 2001 artículo científico 0001-3765 https://www.redalyc.org/articulo.oa?id=32773108 en http://www.redalyc.org/revista.oa?id=327 Anais da Academia Brasileira de Ciências application/pdf Academia Brasileira de Ciências Anais da Academia Brasileira de Ciências (Brasil) Num.1 Vol.73 |
| format | Artículo científico |
| id | redalyc_32773108 |
| language | en |
| publishDate | 2001 |
| publisher | Academia Brasileira de Ciências |
| spellingShingle | Petrography and mineral chemistry of carbonatites and mica-rich rocks from the Araxá complex (Alto Paranaíba Province, Brazil) Gianbosco Traversa Multidisciplinaria (Ciencias Naturales y Exactas) carbonatites geochemistry alkaline rocks Petrography and mineral chemistry of carbonatites and mica-rich rocks from the Araxá complex (Alto Paranaíba Province, Brazil) Gianbosco Traversa Celso B. Gomes Piero Brotzu Nicoletta Buraglini Lucio Morbidelli Maria Speranza Principato Sara Ronca Excelso Ruberti Multidisciplinaria (Ciencias Naturales y Exactas) carbonatites geochemistry alkaline rocks The Araxá complex (16 km2) comprises carbonatites forming a central core and a complex network ofconcentric and radial dykes as well as small veins; additionally, it includes mica-rich rocks, phoscorites andlamprophyres. Fenites also occur and are represented by Proterozoic quartzites and schists of the AraxáGroup.The petrographic study of 130 borehole samples indicates that the complex is basically made up by tworock-types, carbonatites and mica-rich rocks, and subordinately by a third unit of hybrid composition.Carbonatites range chemically in composition, the most abundant type being magnesiocarbonatites. Dolomiteand calcite correspond to the chief constituents, but other carbonate phases, including the Ce-group REminerals, are also recognized. Phosphates and oxides are widespread accessories whereas silicate mineralsconsist of olivine, clinopyroxene, mica and amphibole.Mica-rich rocks are represented by abundant glimmeritic rocks and scarce cumulitic phlogopite-, olivine- anddiopside-bearing pyroxenites. Hybrid rocks mainly contain phlogopite and tetraferriphlogopite as cumulusand intercumulus phases, respectively; carbonate minerals may also be found.Chemical data indicate that the carbonatites are strongly enriched in REE and have lower contents of Nb, Zr,V, Cr, Ni and Rb compared to the mica-rich rocks. The higher K, Nb and Zr contents of the latter rocks arebelieved to be related to metasomatic processes (glimmeritization) of the pyroxenites.Similar REE patterns for carbonatites and mica-rich rocks seem to suggest that they are related to a singleparental magma, possibly of ijolitic composition. Steep LREE/HREE fractionation and high REE contentof some carbonatite samples would be explained by hydrothermal and supergenic processes. 2001 artículo científico 0001-3765 https://www.redalyc.org/articulo.oa?id=32773108 en http://www.redalyc.org/revista.oa?id=327 Anais da Academia Brasileira de Ciências application/pdf Academia Brasileira de Ciências Anais da Academia Brasileira de Ciências (Brasil) Num.1 Vol.73 |
| title | Petrography and mineral chemistry of carbonatites and mica-rich rocks from the Araxá complex (Alto Paranaíba Province, Brazil) |
| topic | Multidisciplinaria (Ciencias Naturales y Exactas) carbonatites geochemistry alkaline rocks |
| url | https://www.redalyc.org/articulo.oa?id=32773108 |