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Geological Society, London, Special Publications; 1999; v. 168; p. 255-272;
DOI: 10.1144/GSL.SP.1999.168.01.17
© 1999 Geological Society of London

Evidence of magmatic hybridization related with feeding zones: the synkinematic Guitiriz granitoid, NW Iberian Massif

M. Menéndez & L. A. Ortega

Departmento de Mineralogía y Petrología, Universidad del País Vasco, Aptdo. 644, Bilbao 48080, Spain npbmemam{at}lg.ehu.es

The hybridization zone of Guitiriz (NW Iberian Massif) displays numerous features resulted from the interaction of two contemporaneously emplaced felsic and intermediate magmas. A combined study, including field geology, petrography, chemistry and Sr isotopic data, reveals a simple two-component mixing between a mantle-derived magma with an initial 87Sr/86Sr isotopic ratio <0.7042 and a crustal-derived component with an initial Sr isotopic ratio > 0.7104. Both magmas rose through a common feeding zone developed in an extensional regime in which favourable conditions for magma mixing occurred. Calculated emplacement temperature and pressure for the Guitiriz hybridization zone are 700 °C and 2.5 kbar, respectively, and are comparable with those estimated from regional metamorphism. Magmatic epidote occurrence, exhibiting textural and compositional characteristics suggestive of magmatic origin, does not require high-pressure granite solidification. Its presence may be related to a rapid magma transport through the feeding zone that favoured the preservation of epidote.