Evolución polifásica de las migmatitas de alta presión del Complejo de Cabo Ortegal. Evidencias a partir de edades U-Pb de circones in situ mediante LA-ICP-MS
- 1 Universidad del País Vasco UPV/EHU
ISSN: 1576-5172
Year of publication: 2012
Issue Title: VIII Congreso Geológico de España, Oviedo, 17-19 de julio, 2012.
Issue: 13
Pages: 829-832
Type: Article
More publications in: Geotemas (Madrid)
Abstract
The migmatitic gneisses of the Bacariza Formation in the Cabo Ortegal complex were formed at ca. 1.8 GPa and 790 °C, with a retrogression stage under amphibolite facies conditions at ca. 0.8 GPa and 650 °C. The electron microscope backscattered images of zircons from those gneisses show oscillatory zoning and overgrowths. A geochronological study has been carried out on a number of zircons which have been analasysed in situ, that is, in thin section, for U-Pb isotope composition using laser ablation and quadrupole mass spectrometry (Q-ICP-MS) techniques. The results obtained yielded several age maxima at ca. 460 Ma, 390 Ma and 360 Ma. The ages of ca. 460 Ma and 390 Ma are interpreted as those of protolith and high-pressure subduction-related metamorphism, respectively. The age around 360 Ma in individual zircons and overgrowths evidences an episode, not previously known from this unit, that involved crystallization of this mineral and for which we propose several possible scenarios.