Evolution of P-T, efective bulk composition, textures and reactions during decompressive retrogression of high T - low P cordierite-ortoamphibole rocks from Osor. Guilleries massif. Variscan metamorphic basement, Catalan Coastal Ranges
- Autores: Joan Reche Estrada, F.J. Martínez Gil
- Localización: Geotemas (Madrid), ISSN 1576-5172, Nº. 6, 1, 2004 (Ejemplar dedicado a: IV Congreso Geológico de España (Zaragoza, 12-15 julio, 2004)), págs. 105-108
- Idioma: español
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Resumen
The Gedrite-antophyllite±garnet±cord¡er¡te±chlor¡te assemblage occur in centimetric amphibolite lenses interlayered within the pre-Caradocian metasediments (semipelites, psamites and high-K2Ö pelites) of the Osor high-T / low-P complex, belonging to the highest grade zones (Sil and Crd-Kfs) of the Variscan metamorphic sequence from the Guilleries Massif (NE Iberia). Textures on the Low-Ca, cordierite-ortoamphibole rocks show evidences of garnet resorption and cordierite growth, leading to stabilization of either cordierite-antophyllite±gedrite±chlorite or garnet-cordierite sub-assemblages in different micro-domains, each characterized by its own reaction space. A retrograde P-T path from peak 5± 1 kbar and 640±40QC follows from the application of classical geothermometers and geobarometers to these amphibolites and to the interlayered metasediments (Reche and Martinez, 2001).
During cooling and decompression, reactions in each of the micro-domains stopped progressively and the volume of the effective reacting systems diminished due to decreasing efficiency of the mass-transfer mechanisms. The modal and compositional trends of garnet, cordierite and ortoamphibole are also in accordance with such a P-T evolution. The presence and textural relations of biotite in most of the samples suggests that the system was open to K20-infiltration during early stages of decompression related to the intrusion of late D2 to early syn-D3 granitoid sheets.
