Kyanite-Staurolite Ortho-Amphibolite from the Chapada Region, Goiás, Central Brazil

Raul Minas Kuyumjian
Instituto de Geociências, Universidade de Brasília, 70910-900 Brasília, Brazil

Abstract: This study deals with the kyanite-staurolite assemblage from a metabasite (ortho-amphibolite) in the Chapada area of the Neoproterozoic Mara Rosa volcano-sedimentary sequence of Goiás state, Brazil. It is closely associated with hydrothermally altered rocks and contains the assemblage hornblende, epidote, quartz, kyanite, staurolite, plagioclase and rutile. The staurolite from the amphibolite shows lower values of SiO2 and higher values of MgO, MnO, ZnO and Xmg than those in staurolites from the metasediments of the same area. In the Al-Na-Ca-(Fe+Mg) diagram, the amphibolite plots in the aluminous part of the diagram and the phase volume encloses the area of mafic volcanic bulk compositions. Field relations and compositions in both kyanite-staurolite amphibolite and staurolite are consistent with formation of this amphibolite as a result of metamorphism of metasomatised basalts.

Keywords: staurolite • ortho-amphibolite • Brazil

Mineralogical Magazine; August 1998 v. 62; no. 4; p. 501-507; DOI: 10.1180/002646198547873
© 1998, The Mineralogical Society
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