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Type: Artigo de periódico
Title: Geochemistry of tourmalines associated with iron formation and quartz veins of the Morro da Pedra Preta Formation, Serra do Itaberaba Group (Sao Paulo, Brazil)
Author: Garda, GM
Beljavskis, P
Juliani, C
Silva, D
Abstract: Tourmalines of intermediate schorl-dravite composition occur in iron formation (including metachert and tourmalinites), metasediments, calc-silicate and metabasic/intermediate rocks of the Morro da Pedra Preta Formation, a volcanic-sedimentary sequence of the Serra do Itaberaba Group (northeast of Sao Paulo City, southeastern Brazil). The Morro da Pedra Preta Formation is crosscut by quartz veins that contain both intermediate schorl-dravite and an alkali-deficient, Cr-(V-)bearing tourmaline, in which the occupancy of the X-site is rectangle(0.51)Ca(0.33)Na(0.15), characterizing it as intermediate to foitite and magnesiofoitite end-members. Mg# values for this tourmaline are higher than those for intermediate schorl-dravite. Raman spectroscopy also confirms the presence of two groups of tourmalines. Stable isotope data indicate sediment waters as fluid sources, rather than fluids from magmatic/post-magmatic sources. Delta(18)O compositions for tourmalines, host metachert, and quartz veins are similar, showing that fluid equilibration occurred during crystallization of both quartz and tourmaline. Syngenetic, intermediate schorl-dravite tourmalines were formed under submarine, sedimentary-exhalative conditions; amphibolite-grade metamorphism did not strongly affect their compositions. Younger tourmalines of compositions intermediate to foitite and magnesiofoitite reflect the composition of the host rocks of quartz veins, due to fluid percolation along faults and fractures that caused leaching of Cr (and V) and the crystallization of these alkali-deficient, Cr-(V-)bearing tourmalines.
Subject: schorl-dravite series
Serra do Itaberaba Group
Morro da Pedra Preta Formation
Country: Brasil
Editor: Acad Brasileira De Ciencias
Citation: Anais Da Academia Brasileira De Ciencias. Acad Brasileira De Ciencias, v. 75, n. 2, n. 209, n. 234, 2003.
Rights: aberto
Identifier DOI: 10.1590/S0001-37652003000200008
Date Issue: 2003
Appears in Collections:Unicamp - Artigos e Outros Documentos

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