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HT‐fabrics in a garnet‐bearing quartzite from Western Portugal: geodynamic implications for the Iberian Variscan Belt

2003; Wiley; Volume: 15; Issue: 2 Linguagem: Inglês

10.1046/j.1365-3121.2003.00472.x

1365-3121

F. J. Fernández, Helder I. Chaminé, Paulo E. Fonseca, J. Munhá, A. Ribeiro, J. Aller, M. Fuertes-Fuente, Frederico Sodré Borges,

earthquake and tectonic studies

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.