| Texto completo | |
| Autor(es): |
GIANBOSCO TRAVERSA
[1]
;
CELSO B. GOMES
[2]
;
PIERO BROTZU
[3]
;
NICOLETTA BURAGLINI
[4]
;
LUCIO MORBIDELLI
[5]
;
MARIA SPERANZA PRINCIPATO
[6]
;
SARA RONCA
[7]
;
EXCELSO RUBERTI
[8]
Número total de Autores: 8
|
| Afiliação do(s) autor(es): | [1] Università di Roma La Sapienza. Dipartimento di Scienze della Terra - Itália
[2] Universidade de São Paulo. Instituto de Geociências - Brasil
[3] Università di Napoli. Dipartimento di Scienze della Terra - Itália
[4] Università di Catania. Dipartimento Scienze della Terra
[5] Università di Roma La Sapienza. Dipartimento di Scienze della Terra - Itália
[6] Università di Milano. Dipartimento Scienze della Terra - Itália
[7] Università di Roma La Sapienza. Dipartimento di Scienze della Terra - Itália
[8] Universidade de São Paulo. Instituto de Geociências - Brasil
Número total de Afiliações: 8
|
| Tipo de documento: | Artigo Científico |
| Fonte: | Anais da Academia Brasileira de Ciências; v. 73, n. 1, p. 71-98, 2001-03-00. |
| Resumo | |
The Araxá complex (16 km²) comprises carbonatites forming a central core and a complex network of concentric and radial dykes as well as small veins; additionally, it includes mica-rich rocks, phoscorites and lamprophyres. Fenites also occur and are represented by Proterozoic quartzites and schists of the Araxá Group. The petrographic study of 130 borehole samples indicates that the complex is basically made up by two rock-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. Dolomite and calcite correspond to the chief constituents, but other carbonate phases, including the Ce-group RE minerals, are also recognized. Phosphates and oxides are widespread accessories whereas silicate minerals consist of olivine, clinopyroxene, mica and amphibole. Mica-rich rocks are represented by abundant glimmeritic rocks and scarce cumulitic phlogopite-, olivine- and diopside-bearing pyroxenites. Hybrid rocks mainly contain phlogopite and tetraferriphlogopite as cumulus and 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 are believed 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 single parental magma, possibly of ijolitic composition. Steep LREE/HREE fractionation and high sigmaREE content of some carbonatite samples would be explained by hydrothermal and supergenic processes. (AU) | |
| Processo FAPESP: | 97/01210-4 - Petrologia e geoquímica de rochas alcalinas |
| Beneficiário: | Celso de Barros Gomes |
| Modalidade de apoio: | Auxílio à Pesquisa - Temático |