Abstract

In E Connemara, Ireland, Dalradian metasediments were initially metamorphosed to kyanite-staurolite grade at pressures above 7kbar. The subsequent emplacement of basic to intermediate magmas, accompanied by uplift and erosion, produce a steepening of the geothermal gradient and led to the formation of migmatitic garnet–cordierite–sillimanite-gneisses in the highest grade regions in the S. Cation exchange equilibria between coexisting mineral pairs suggest that partial melting took place under high temperatures (≃ 750°C) and moderate pressures (4.5–6 kbar). Fluid inclusion studies and andalusite occurrences from migmatite leucosomes suggest that crystallization of the melts occurred at lower pressures (<3.5 kbar) than melting, implying that uplift and erosion occurred while the rocks were hot.

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