FIELD AND PETROGRAPHIC EVIDENCE FOR MAGMA MIXING AND MINGLING IN GRANITOIDS: EXAMPLES FROM THE GALWAY GRANITE, CONNEMARA, IRELAND
Petrographic studies of both the MME and their host rocks have revealed a range of textures attributable to mafic-felsic magma interaction: quartz ocelli, rapakivi feldspars, acicular and mixed apatite morphologies, inclusion zones in feldspars, anorthite spikes in plagioclase, sphene ocelli, K-feldspar megacrysts in MME, and mafic clots. Variations in the abundance of each texture in different hybrids, even those hybrids which have a close spatial relationship, suggest mixing occurred under different conditions and at different times: ie. there is strong evidence for multiple mixing events. Furthermore, textures from this assemblage have been recorded throughout the Galway batholith, even in relatively felsic lithologies, indicating that mafic-felsic magma interaction played a key role during the evolution of the batholith.
Finally, the ubiquity of mixing textures, even in the most mafic of MME, prompts the question do any true mafic end member lithologies remain at the present exposure level of the batholith? a question that must be addressed when choosing end member lithologies for magma mixing models.