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Experimental Melting of Cordierite Gneiss and the Petrogenesis of Syntranscurrent Peraluminous Granites in Southern Brazil |
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| Authors: | KOESTER EDINEI; PAWLEY ALISON R; FERNANDES LUIS A D; PORCHER CARLA C; SOLIANI ENIO JR |
| Institution: | 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 |
| Abstract: | To understand the petrogenesis of peraluminous granites syntectonicto the Dorsal de Canguçu Transcurrent Shear Zone in theSul-rio-grandense Shield, Brazil, melting experiments were performedon one of the potential protoliths, a cordierite-bearing semi-peliticmetasedimentary gneiss (PE-1). Experiments were conducted atpressures of 5, 10 and 15 kbar, at temperatures of 700–900°C,and under fluid-absent and 5% H2O-present conditions. The experimentsshow that fluid-absent melting begins at near-solidus conditions,around 700°C, promoted by participation of retrogressivephengitic muscovite in the reaction Mus + Kf ± Qz = melt± Fe–Ti oxide ± Als, producing a very smallamount of melt (<9%) with widely ranging composition. Allhypersolidus experiments (>800°C) produced S-type graniticmelts promoted by participation of biotite or cordierite inthe 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 ofmelt (10–63% by volume). The melt compositions obtainedat 900°C and 15 kbar under fluid-absent conditions, promotedby biotite or cordierite breakdown, are similar to the syntectonicgranites. However, it is unlikely that the granites were formedat this pressure (corresponding to a depth of melting of |
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