SIGNIFICADO DA OCORRÊNCIA DE FOSFATOS E BORATOS DE ALUMÍNIO NO CONTATO ENTRE OS SUPERGRUPOS RIO PARAÚNA E ESPINHAÇO NA REGIÃO DE DIAMANTINA, MINAS GERAIS, BRASIL

Within a muscovite-kyanite quartzite and/or muscovite-kyanite schist at the contact between the UpperArchean Barao de Guacui Formation and the Bandeirinha Formation near Diamantina (State of MinasGerais, Brazil) five rock types defining mineral assemblages can be found: 1: lazulite, kyanite, 2: lazulite,augelite, kyanite; 3: lazulite, amblygonite, tourmaline; 4: lazulite, svanbergite, tourmaline, and 5:dumortierite, kyanite. Additional phases in all rock types are quartz and muscovite/sericite. The wholerock chemistry influences the chemical composition of the individual minerals.These ocurrences are interpreted as precipitation of aluminium, phosphorous and boron-rich sedimentaryrocks in highly alcaline lakes under sabka conditions in the Middle Proterozoic on the Archeanmetasediments of the Barao de Guacui Formation.During the Brasiliano event (680-450Ma) a greenschist metamorphism and associated tectonism withthrusting the actual texture and foliation were formed. Mobilization of lazulite and its deposition intoquartz veins, cutting the over- and underlain units occurred, too.The aluminophosphate minerals get importance because they could help to define more precisely thecontact between the Rio Parauna and Espinhaco supergroups.

[1]  G. Morteani,et al.  Aluminium phosphates in muscovite-kyanite metaquartzites from Passo di Vizze (Alto Adige, NE Italy) , 1996 .

[2]  Ivo Antônio Dussin.  Evolution structurale de la region de l'espinhaco meridional, bordure sud-est du craton sao francisco bresil : tectoniques superposees au proterozoique , 1994 .

[3]  L. Knauer,et al.  A ORIGEM DOS FILITOS HEMATÍTICOS DA SERRA DO ESPINHAÇO MERIDIONAL, MINAS GERAIS , 1993 .

[4]  P. A. A. Abreu.  Geologia das quadrículas Cuiabá e Onça: Gouveia-MG - região mediana central , 1993 .

[5]  G. Einsele.  Sedimentary Basins: Evolution, Facies, and Sediment Budget , 1992 .

[6]  J. Schorscher,et al.  Cover/basement relationships in the southern Serra do Espinhaço, Minas Gerais, Brazil , 1992 .

[7]  L. Knauer,et al.  Evolução geologica do pre-cambriano da porção centro-leste da serra do Espigão meridional e metalogenese associada , 1990 .

[8]  J. Cassedanne,et al.  Origine des Lazulites Liees a des accidents ferriferes dans des quartzites a dumortierite (Serra da Vereda, Bahia, Bresil) , 1989 .

[9]  W. Schreyer.  Pre- or Synmetamorphic Metasomatism in Peraluminous Metamorphic Rocks? , 1987 .

[10]  R. Pflug,et al.  The Thrust Belt of the Southern Serra do Espinhaço, Minas Gerais, Brazil , 1986 .

[11]  Gao Jian,et al.  Tidal sedimentary structures from upper precambrian rocks of the Ming Tombs District, Beijing (Peking), China , 1985 .

[12]  K. H. Wedepohl.  Handbook of Geochemistry , 1969 .

[13]  J. Dorr.  Physiographic, stratigraphic, and structural development of the Quadrilatero Ferrifero, Minas Gerais, Brazil , 1969 .

[14]  J. Fahey,et al.  The lazulite-scorzalite isomorphous series , 1950 .