New age constraints for the Ordovician Tyrone Volcanic Group, Northern Ireland

• Published in: Journal of the Geological Society Vol. 165; no. 1; pp. 333 - 339
• Main Authors: Cooper, Mark R, Crowley, Q. G, Rushton, A. W. A
• Format: Journal Article
• Language: English
• Published: London Geological Society of London 01.01.2008; The Geological Society of London; Geological Society; Geological Society Publishing House
• Subjects: absolute age; Arenigian; Ballantrae Complex; biostratigraphy; correlation; Crystalline rocks; Didymograptina; Earth sciences; Earth, ocean, space; Europe; Exact sciences and technology; Geochronology; Geology; Graptolithina; Graptoloidea; Great Britain; Igneous and metamorphic rocks petrology, volcanic processes, magmas; igneous rocks; Isograptus; Isograptus victoriae lunatus; Lower Ordovician; mass spectra; Middle Ordovician; Midland Valley; nesosilicates; Northern Ireland; Ordovician; orthosilicates; Paleozoic; Plate tectonics; Polls & surveys; rhyolites; Scotland; silicates; Slieve Gallion; spectra; Stratigraphy; thermal ionization mass spectra; Tyrone Complex; Tyrone Volcanic Group; U/Pb; United Kingdom; volcanic rocks; Western Europe; Whitlandian; zircon; zircon group; Great Britain; Europe; England; United Kingdom; Scotland; Northern Ireland; Midlands; Tyrone Northern Ireland; Western Europe; Chordata; Didymograptina; accuracy; isotope dilution; index fossils; zircon; Terranes; silicates; graptolites; Protochordata; clastic rocks; nesosilicates; mudstone; volcanic rocks; volcanic arcs; Hemichordata; Middle Ordovician; Ordovician; igneous rocks; rhyolites; U/Pb; Paleozoic; sedimentary rocks; correlation; Isograptus; Graptolithina; Graptoloidea; valleys
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/0016-76492007-057

New biostratigraphical evidence and a high-precision isotope dilution thermal ionization mass spectrometry U-Pb zircon age provide refined age constraint for the Ordovician Tyrone Volcanic Group of the Tyrone Igneous Complex. In a graptolite fauna from Slieve Gallion, the presence of Isograptus victoriae lunatus, the index fossil of the victoriae lunatus graptolite zone, indicates a correlation with the Australasian Castlemainian (Ca1) Stage. The U-Pb zircon age of 473±0.8 Ma dates a volcanic arc-related rhyolite body that is stratigraphically below graptolitic mudstones of Slieve Gallion. The U-Pb isotopic and biostratigraphical age constraints closely match an interpolated age for the base of the Middle Ordovician and indicate a Whitlandian age for the upper Tyrone Volcanic Group, which supports the regional correlation with the Ballantrae Complex, Midland Valley Terrane, Scotland.