Age constraints and geochemistry of the Ordovician Tyrone Igneous Complex, Northern Ireland: implications for the Grampian orogeny

Abstract

arc-related rocks exposed along the northern margin of Iapetus within the British and 21

High-precision U–Pb dating of complex zircon from the Lewisian Gneiss Complex of Scotland using an incremental CA-ID-TIMS approach

“…Bergh et al, 2007;Borradaile and Geneviciene, 2008;Kolb et al, 2013). In addition to these areas, it is thought that rocks of Lewisian affinity form unexposed basement over a large area of the North Atlantic region (Hitchen, 2004;Flowerdew et al, 2009;O'Driscoll et al, 2009;Cooper et al, 2011). Tectonothermal events, including formation of early granulites retrogressed during a later amphibolite facies event, recorded by the Lewisian gneisses are also found in many cratons worldwide Santosh et al, 2013;Jiang et al, 2013;Rekha et al, 2013;Verma and Verma, 2013) and appear to represent periods of significant crustal growth.…”

A review of geological origins and relationships in the Ballantrae Complex, SW Scotland

“…The TVG lavas show evidence of contamination by continental material (Draut et al 2009;Cooper et al 2011) and are thought to have been erupted in a peri-Laurentian island-arc to back-arc environment, which underwent several episodes of intra-arc rifting (Hollis et al 2012). Accretion to the outboard peri-Laurentian microcontinental block now represented by the Tyrone Central Inlier followed soon after obduction of the TPG, and was also complete by about 470 Ma.…”

“…There are two structurally distinct parts to the Tyrone Igneous Complex, designated the Tyrone Plutonic Group (TPG) and the Tyrone Volcanic Group (TVG) (Cooper & Mitchell 2004). The TPG preserves the uppermost portion of a dismembered, supra-subduction zone ophiolite (Cooper et al 2011) with layered, isotropic and pegmatitic gabbros, sheeted dolerite dykes and rare basaltic pillow lavas. U-Pb isotopic dates from the gabbros range approximately from 484 Ma (Hollis et al in press a) to 480 Ma (Cooper et al 2011), with obduction onto the Tyrone Central Inlier basement occurring prior to about 470 Ma.…”

“…The TPG preserves the uppermost portion of a dismembered, supra-subduction zone ophiolite (Cooper et al 2011) with layered, isotropic and pegmatitic gabbros, sheeted dolerite dykes and rare basaltic pillow lavas. U-Pb isotopic dates from the gabbros range approximately from 484 Ma (Hollis et al in press a) to 480 Ma (Cooper et al 2011), with obduction onto the Tyrone Central Inlier basement occurring prior to about 470 Ma. The latter date is constrained by the ages of postobduction intrusions that range between about 470 Ma and 464 Ma, which contain xenocrystic Proterozoic zircons, and have strongly negative ƐNdt values (Draut et al 2009;Cooper et al 2011;Hollis et al 2012).…”

“…Ma (Cooper et al 2011;Hollis et al 2012). The TVG lavas show evidence of contamination by continental material (Draut et al 2009;Cooper et al 2011) and are thought to have been erupted in a peri-Laurentian island-arc to back-arc environment, which underwent several episodes of intra-arc rifting (Hollis et al 2012).…”