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HT-fabrics in a garnet-bearing quartzite from Western Portugal: geodynamic implications for the Iberian Variscan Belt |
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| Authors: | Francisco J Fernández Helder I Chaminé Paulo E Fonseca José M Munhá António Ribeiro Jesus Aller Mercedes Fuertes-Fuentes Frederico S Borges |
| Institution: | Departamento de Geología, Universidad de Oviedo. Arias de Velasco s/n, 33005 Oviedo, Spain;;Departamento de Geociências (MIA), Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal;;Departamento de Geologia (LATTEX and CGUL), Universidade de Lisboa, C2–5 piso, Campo Grande, 1749-061 Lisbon, Portugal;;Departamento de Geologia (CGUP), Universidade do Porto, Praça de Gomes Teixeira, 4099-002 Porto, Portugal |
| Abstract: | ABSTRACT The study of a garnet-bearing quartzite from a major suture zone in Iberia reports an unusual high-T fabric. Quartz c -axis patterns were plotted using shaped garnet as reference axis for the finite stretch ( X -axis). The pole figures are characterized by a dominant single maximum around X together with other point maxima along the XY plane (mylonitic foliation). These patterns suggest that dominant < c > prism slip and subordinated < a > prism slip operated during quartz plastic deformation in agreement with P–T conditions for syntectonic garnet growth (4–5 kbar and 700 ± 50 °C) and, pre-dating the well-known (late) Variscan D1 event (<6 kb and 600 ± 30 °C). The geotectonic framework suggests that the fabrics were formed along the western shear margin of the Ossa-Morena Zone during the early stages of the Variscan orogeny. |
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