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vol.79 número3The Serra da Graciosa A-type granites and syenites, southern Brazil. Part 1: regional setting and geological characterizationStructural and geochronological constraints on the evolution of the Juréia Massif, Registro Domain, State of São Paulo, Brazil índice de autoresíndice de assuntospesquisa de artigos
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Anais da Academia Brasileira de Ciências

versão impressa ISSN 0001-3765versão On-line ISSN 1678-2690

Resumo

VIANA, Rúbia R.; EVANGELISTA, Hanna J.  e  STERN, Willem B.. Chemical zoning of muscovite megacrystal from the Brazilian Pegmatite Province. An. Acad. Bras. Ciênc. [online]. 2007, vol.79, n.3, pp.431-439. ISSN 0001-3765.  http://dx.doi.org/10.1590/S0001-37652007000300007.

Macroscopically homogenous muscovite plate from the Cruzeiro pegmatite, located in the Eastern Pegmatite Province in Minas Gerais, may show complex distribution patterns of some trace elements. In geochronological and petrological studies, as for example in the distinction of magmatic and post-magmatic mica, the cause of zoning could be taken into consideration. The complex chemical zoning in the studied mica plate can be best explained by growth in an evolving magma followed by alteration due to percolation of hydrothermal fluids. Enrichment of Rb towards the border is interpreted as resulting from the chemical evolution of the residual magma during crystal growth. The depletion in (IVAl+VIAl) as well as the increase in (Fe+Mg) and Si along a fracture could be due to the hydrothermal celadonitic substitution of muscovite. This alteration also caused depletion in the contents of Rb, Ga, Y, Nb, Sn, and Zn and residual concentration of Ti. Elements such as Ga, Y, Nb, Sn, and Zn, rarely considered in the discussion of differentiation or alteration processes in micas, have been shown to be as significant as the alkali-elements.

Palavras-chave : muscovite; chemical zoning; hydrothermal alteration; Cruzeiro pegmatite.

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