Quartz recrystallization regimes, c-axis texture transitions and fluid inclusion reequilibration in a prograde greenschist to amphibolite facies mylonite zone (Ribeira Shear Zone, SE Brazil)

Autor(es)

Faleiros, Frederico Meira ^{[1, 2]} ; da Cruz Campanha, Ginaldo Ademar ^[2] ; da Silveira Bello, Rosa Maria ^[2] ; Fuzikawa, Kazuo ^[3]

Afiliação do(s) autor(es)

^[1] CPRM Geol Survey Brazil, BR-01304010 Sao Paulo - Brazil

^[2] Univ Sao Paulo, Dept Mineral & Geotecton, Inst Geociencias, BR-05508900 Sao Paulo - Brazil

^[3] CDTN CNEN, Lab Inclusoes Fluidas & Metalogenese, BR-66075900 Belo Horizonte, MG - Brazil

• Tipo de documento: Artigo Científico
• Fonte: TECTONOPHYSICS; v. 485, n. 1-4, p. 193-214, APR 1 2010.
• Citações Web of Science: 31

Resumo

The crystal-plastic behavior of quartz mylonites from the Ribeira Shear Zone (SE Brazil), a major strike-slip structure that was active during a prograde metamorphic phase related to the Neoproterozoic Brasiliano-Pan African Orogeny, was investigated using a multi-method approach. Geothermobarometry results indicate deformational conditions ranging from similar to 300 to similar to 630 degrees C and 500-700 MPa. A strong correlation between mapped metamorphic zones and a dominance of different dynamic recrystallization mechanisms of quartz occurs within the mylonite zone. Bulging recrystallization (BLG) dominates within the chlorite zone between 300 and 410 degrees C, subgrain rotation recrystallization (SGR) operates within the biotite zone from 410 to 520 degrees C, and grain boundary migration recrystallization (GBM) dominates in the garnet zone above 520 degrees C. The development of quartz c-axis textures is mainly governed by temperature and dynamic recrystallization mechanisms. Textures from BLG zone mylonites are characterized by maxima around Z; SGR zone mylonites display single girdles or asymmetric type I crossed girdles; and GBM zone mylonites comprise maxima around Y and intermediate between X and Z. The scarcity or absence of water-bearing fluid inclusions in quartz mylonites from the SGR and GBM zones, which are dominated by carbonic inclusions, suggests water-deficient conditions, whereas BLG zone mylonites are dominated by water-bearing inclusions. This evidence indicates that water was available in the protoliths but has been eliminated with increasing deformation and deformation temperature. No effect of the water content variation on the quartz microstructural and recrystallized grain size evolution was detected, and little influence on c-axis texture development was observed. Most of the fluid inclusion densities were reequilibrated during the shear zone exhumation history, recording a decompression in the range of 300-500 MPa, while microstructural reequilibration effects related to the prograde metamorphism are largely preserved. Fluid inclusion microstructures and densities from two SGR zone samples preserved evidence for a near isothermal compression within the interior of the Ribeira Shear Zone during the prograde metamorphism. (C) 2009 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 02/13654-4 - Caracterização de terrenos tectono-metamórficos no extremo Sul do estado de São Paulo
• Beneficiário: Frederico Meira Faleiros
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 01/13457-1 - Caracterização isotópica de rochas dos subgrupos Ribeira e Lajeado na região de Iporanga, SP
• Beneficiário: Ginaldo Ademar da Cruz Campanha
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 06/01327-0 - Caracterizacao metamorfica, estrutural e geocronologica de terrenos pre-cambrianos no sul do estado de sao paulo.
• Beneficiário: Ginaldo Ademar da Cruz Campanha
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 01/00199-4 - Padrões geométricos, cinemáticos e nível crustal da zona de cisalhamento Ribeira
• Beneficiário: Frederico Meira Faleiros
• Modalidade de apoio: Bolsas no Brasil - Mestrado