Abstract

Recent studies on shallow-level arcuate intrusions have identified numerous examples of horizontal mineral fabrics. These are commonly interpreted as reflecting considerable lateral flow during magma emplacement, thus querying established ‘semi-vertical’ ring-dyke models. We question the recent lateral emplacement model proposed for the Palaeocene Slieve Gullion Ring-complex, NE Ireland, where the absence of steep fabrics in parts of the ring-complex has been used to support a shallow, semi-horizontal sheet intrusion mechanism. We argue that such simple flow models cannot be applied to explosive ring-fissure eruptions and that fabric data alone do not warrant rejection of the ring-dyke model. Moreover, the apparent ‘absence of steep intrusive contacts’ along the intrusion’s perimeter is readdressed and we present numerous examples of outcrops (27) with steep-sided geometries. The Camlough Breccias are reinterpreted as the product of gas-driven tuffisites injected along the active ring-fault (rather than of purely tectonic origin). Crucially, the porphyritic microgranite and porphyritic rhyolite ring-dyke rocks exhibit geochemical and petrographic signatures of contamination by the geographically restricted Palaeozoic Newry granodiorite and are best explained through crustal interaction vertically beneath the ring-complex. Subsequently, these silicic magmas rose into ignimbrite feeders along a caldera ring-fault system that was emplaced into near-surface vent-filling breccias.

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