SciELO - Scientific Electronic Library Online

vol.72 número3Minerales asbestiformes en vermiculitas del sector centro-occidental de la provincia de CórdobaProcesos metamórficos y metasomáticos en el skarn Loma Marcelo, basamento Neoproterozoico de las sierras Australes de la provincia de Buenos Aires índice de autoresíndice de assuntospesquisa de artigos
Home Pagelista alfabética de periódicos  

Serviços Personalizados




  • Não possue artigos citadosCitado por SciELO

Links relacionados

  • Não possue artigos similaresSimilares em SciELO


Revista de la Asociación Geológica Argentina

versão impressa ISSN 0004-4822versão On-line ISSN 1851-8249


MARTINEZ, Juan C; MASSONNE, Hans J; DRISTAS, Jorge A  e  FRISICALE, María C. Genesis of dioctahedral K- and Na-bearing micas at the strongly altered late proterozoic unconformity of the Tandilia belt, central-eastern Argentina. Rev. Asoc. Geol. Argent. [online]. 2015, vol.72, n.3, pp.385-403. ISSN 0004-4822.

The unconformity-related phyllosilicate mineral assemblages of the most pervasively altered basement of the Tandilia belt, central Buenos Aires Province, were studied from two ~50 km distant areas, Barker and San Manuel. The secondary dioctahedral K-white micas show a compositional spread probably by a solid-solution towards pyrophyllite. In addition, electron microprobe analyses of micas yielded widely variable Na* [Na/(Na+K+Ca+Ba)] ratios, which can be related to a compositional range between nearly pure muscovite and intermediate micas with maximum paragonite contents corresponding to muscovite55paragonite45 and muscovite40 paragonite60 for the Barker and San Manuel areas, respectively. Scanning electron images suggest the local occurrence of paragonite/intermediate K-Na white micas, finely intergrown within secondary K-white mica and pyrophyllite. P-T pseudosections (H2O saturated) in the Na-K-Fe-Mg-Mn-Al-Si-Ti-O-H system for different XFe3+ (Fe+3/Fetot) constrain temperatures of formation of the secondary mineral assemblages around 280 - 340 ºC, whereas such mineral assemblages are almost insensitive to pressure between 0.5 and 5 kbar. At these P-T conditions, the most likely mineral assemblages include K-white mica, chloritoid, rutile, and hematite (± pyrophyllite ± paragonite). An additional phase is either quartz, which was observed as relic of the protolith, or diaspore. A 40Ar/39Ar step-heating age of 630 ± 30 Ma on a K-white mica rich sample linked the hydrothermal alteration event to the Brasiliano orogenic cycle.

Palavras-chave : K-Na bearing micas; Altered basement; Tandilia Late Proterozoic Unconformity; 40Ar/39Ar step-heating thermochronology; Thermodynamic modeling.

        · resumo em Espanhol     · texto em Inglês


Creative Commons License Todo o conteúdo deste periódico, exceto onde está identificado, está licenciado sob uma Licença Creative Commons