Journal of Petrology | Volume 43 | Number 8 | Pages 1595-1616 | 2002
© Oxford University Press 2002
Experimental Melting of Cordierite Gneiss and the Petrogenesis of Syntranscurrent Peraluminous Granites in Southern Brazil
1PROGRAMA DE PÓS-GRADUAÇÃO EM GEOCIÊNCIAS, UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL, PORTO ALEGRE, 91509-900, RS, BRAZIL
2DEPARTMENT OF EARTH SCIENCES, UNIVERSITY OF MANCHESTER, MANCHESTER M13 9PL, UK
3CENTRO DE PETROLOGIA E GEOQUÍMICA, INSTITUTO DE GEOCIÊNCIAS, UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL, PORTO ALEGRE, 91509-900, RS, BRAZIL
To understand the petrogenesis of peraluminous granites syntectonic to the Dorsal de Canguçu Transcurrent Shear Zone in the Sul-rio-grandense Shield, Brazil, melting experiments were performed on one of the potential protoliths, a cordierite-bearing semi-pelitic metasedimentary gneiss (PE-1). Experiments were conducted at pressures of 5, 10 and 15 kbar, at temperatures of 700–900°C, and under fluid-absent and 5% H2O-present conditions. The experiments show that fluid-absent melting begins at near-solidus conditions, around 700°C, promoted by participation of retrogressive phengitic muscovite in the reaction Mus + Kf ± Qz = melt ± Fe–Ti oxide ± Als, producing a very small amount of melt (<9%) with widely ranging composition. All hypersolidus experiments (>800°C) produced S-type granitic melts promoted by participation of biotite or cordierite in the reactions Bio + Pl + Crd + Qz = Px + Fe–Ti oxide + melt at 5 kbar, and Bio + Pl + Crd ± Qz = Grt + Als ± Kf + melt at 10 and 15 kbar, both producing a high amount of melt (10–63% by volume). The melt compositions obtained at 900°C and 15 kbar under fluid-absent conditions, promoted by biotite or cordierite breakdown, are similar to the syntectonic granites. However, it is unlikely that the granites were formed at this pressure (corresponding to a depth of melting of 
54 km).
KEY WORDS: cordierite gneiss; fluid-absent and H2O-present melting experiments; peraluminous granites; shear zone
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