Lateral versus vertical emplacement in shallow-level intrusions? : The Slieve Gullion Ring-complex revisited

• 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.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Keyword

Endogenous earth sciences

Endogen geovetenskap

Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics

Geovetenskap med inriktning mot mineralogi, petrologi och tektonik

Publication and Content Type

ref (subject category)

art (subject category)