Metamorphic conditions in central Connemara, Ireland

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Abstract
Metamorphic conditions have been estimated for an area in central Connemara that includes Cashel and Lissoughter Hill. Pressures lie in the range 3.0–6.0 kbar. Temperatures increase from 625–675°C on the N slopes of Lissoughter Hill to 650–700°C on the S slopes, to 700–750°C in the migmatized metasediments N of the Cashel ultrabasic intrusion before increasing sharply towards the contact. Away from the area adjacent to the intrusion a horizontal thermal gradient of between 30°C and 40°C/km may be inferred. Differences in the relative spatial position with increasing temperature of the staurolite-out, muscovite and quartz-out and beginning of partial melting isograds imply that the rocks exposed at the eastern end of the steep belt at Maam Cross were metamorphosed at a lower pressure than those farther W at Recess. Similarly, the stable co-existence of muscovite and quartz in the Recess area may indicate that the second sillimanite isograd dips towards the S, a condition that would be consistent with sub-vertical isotherms associated with a thermal anticline centred on the Cashel volcanic arc.