Diorite-granite magma mingling and mixing along the axis of the Galway Granite batholith, Ireland

The late Caledonian Galway Granite batholith is bisected by a WNW-trending magma mingling and mixing zone (the MMZ). This trans-batholithic feature marks the entrainment and ascent of hydrous dioritic magmas in anatectic silicic magmas. Deep in the zone, flowage and hydraulic stress stretched out alternating mafic and hybrid granitoid sheets. At progressively shallower levels, highly elongate and deformed enclaves led up to discrete clouds of ovoid enclaves. Magmatic end-members are identified as quartz diorite and calc-alkaline granite, from which a mixing continuum was produced despite a persistent degree of immiscibility among the various hybrids. A generally west-directed flowage along the MMZ locally induced detachment and upthrusting of ductile blocks of deeper-seated mingled rock. The detailed plan of the MMZ reveals left offsets, supporting field evidence for emplacement in a broad dextral NW-SE shear zone. The Maam and Clifden fault systems provide the partners to model this emplacement within a crustal pull-apart.