Evolution of the Tyrone ophiolite, Northern Ireland, during the Grampian–Taconic orogeny: a correlative of the Annieopsquotch Ophiolite Belt of central Newfoundland?

Abstract

The Tyrone Plutonic Group of Northern Ireland represents the upper portions of a tectonically dissected suprasubduction-zone ophiolite accreted to the composite Laurentian margin during the Middle Ordovician. Understanding its development and relationship to the Tyrone Central Inlier, an outboard fragment of relatively high-grade, peri-Laurentian continental crust, is essential for reconstructing the closure of the Iapetus Ocean. The Tyrone Plutonic Group is composed of tectonized layered, isotropic and pegmatitic gabbros, sheeted dolerite dykes and rare pillow lavas. New U–Pb zircon thermal ionization mass spectrometry geochronology has yielded an age of 483.68 ± 0.81 Ma from pegmatitic gabbro. Geochemical characteristics, Nd and Sr isotope systematics, and zircon inheritance indicate that the Tyrone Plutonic Group formed above a north-dipping subduction zone, by the propagation of a spreading centre into a microcontinental block. Synkinematic, calc-alkaline tonalitic to granitic material preserved in the contact zone between the Tyrone Plutonic Group and the Tyrone Central Inlier has produced pressure estimates of 2.3–4.0 ± 0.6 kbar and temperatures of 525–610 °C. Coeval arc–ophiolite accretion at c . 470 Ma may explain how sillimanite-grade metamorphic conditions were reached locally in the underlying Tyrone Central Inlier. Strong temporal, geochemical and lithological similarities exist to the Annieopsquotch Ophiolite Belt of Newfoundland. Supplementary materials: Petrographic photographs, whole-rock, isotopic and mineral geochemical data, and U–Th–Pb isotopic data are available at www.geolsoc.org.uk/SUP18646 .

Evidence for an Early Silurian Synorogenic Basin Within the Metamorphic Hinterland of the North Atlantic Caledonides: Insights From the U‐Pb Zircon Geochronology of the Funzie Conglomerate, Shetland, Scotland

“…Supra-subduction zone ophiolites are exposed in Clew Bay and Tyrone (Ireland), Bute (SW Scotland), Ballantrae (S Scotland), and Shetland (Figure 1a; e.g., Gass et al, 1982;Prichard, 1985;Spray & Dunning, 1991;Kawai et al, 2008;Chew et al, 2010). In Ireland, magmatic arcs are exposed south of Clew Bay (Dewey & Mange, 1999) and in Tyrone (Hollis et al, 2012(Hollis et al, , 2013 but, in Scotland, are thought to be buried beneath the Upper Paleozoic cover successions of the Midland Valley Terrane (Bluck, 2002). Following a flip in subduction polarity and development of the Southern Uplands accretionary prism in Scotland and Ireland (Figure 1a; Leggett et al, 1979;Stone & Merriman, 2004), renewed deformation and metamorphism at ca.…”

The Ordovician Grampian Orogeny, Western Ireland: Obduction Versus “Bulldozing” During Arc‐Continent Collision

“…They should be distinguished from ophiolitic mélanges, which may have a complex evolutionary history. These fore-arc ophiolites formed during an~15-my interval straddling the Cambrian-Tremadoc boundary and include ( Figure 4) the Unst ophiolite of the Shetland Islands (492±3 Ma (Spray & Dunning, 1991) and 484±4 Ma obduction age (Crowley & Strachan, 2015)); the Bute ophiolite of the Highland Border Complex, Scotland (499 ± 8 Ma and 490 ± 4 or 488 ± 1 Ma obduction ages; Chew et al, 2010); the Tyrone Plutonic Group, Northern Ireland (483.68 ± 0.81 Ma; Hollis et al, 2013); and in Newfoundland the St Anthony complex (>489 ± 5 Ma) and the Bay of Island ophiolitic complex (485.7 +1.9 / -1.2 Ma; Dunning & Krogh, 1985). We now discuss the factors that controlled the widespread obduction of the arc and forearc during the Grampian-Taconic arc-continent collision.…”

Age and Geologic Setting of Quartz Vein-Hosted Gold Mineralization at Curraghinalt, Northern Ireland: Implications for Genesis and Classification

“…Two gold deposits, Curraghinalt and Cavanacaw, and some minor gold mineralization follow the Fair Head-Clew Bay Line in the north of Ireland. Dalradian sedimentation was terminated by an arccontinent collision in the Ordovician (Grampian event of the Caledonian orogeny; Hollis et al, 2013a). Polyphase deformation and regional metamorphism in the Dalradian of western Ireland is dated to between ca.…”

“…475 to 469 Ma Tyrone Volcanic Group island arc onto an outboard microcontinental block prior to ca. 470 Ma during the Grampian event of the Caledonian orogeny (Cooper et al, 2008(Cooper et al, , 2011Hollis et al, 2012Hollis et al, , 2013a. Various arc-related granitoids intruded the Tyrone Volcanic Group following a reversal of subduction polarity and have been dated at ca.…”