Geochronological constraints on the magmatic, metamorphic and thermal evolution of the Connemara Caledonides, western Ireland

• Published in: Journal of the Geological Society Vol. 156; no. 6; pp. 1217 - 1230
• Main Authors: Friedrich, Anke M, Hodges, Kip V, Bowring, Samuel A, Martin, Mark W
• Format: Journal Article Conference Proceeding
• Language: English
• Published: London Geological Society of London 01-11-1999; The Geological Society of London; Geological Society
• Subjects: absolute age; anatexis; Ar/Ar; Caledonides; chemical composition; Connemara; cooling; Crystalline rocks; dates; Earth sciences; Earth, ocean, space; electron probe data; emplacement; Europe; Exact sciences and technology; Galway Ireland; geochemistry; Geochronology; igneous and metamorphic rocks; Igneous and metamorphic rocks petrology, volcanic processes, magmas; intrusions; Ireland; magmatism; metamorphism; Middle Ordovician; Ordovician; Paleozoic; Petrology; plutons; rates; Tectonics. Structural geology. Plate tectonics; thermal history; U/Pb; Western Europe; Galway Ireland; Connemara; Ireland; Western Europe; Ar; deformation; magmatism; metamorphism; Connemara; U-Pb; metapelite; diorites; tectogenesis; calc-alkalic composition; gabbros; Caledonides; quartz diorites; thermal evolution; zircon; granites; silicates; dating; migmatites; nesosilicates; Europe; Middle Ordovician; Ordovician; anatexis; igneous rocks; U/Pb; metamorphic rocks; Paleozoic; plutonic rocks; cooling; metasedimentary rocks; Ar-40/Ar-39; pegmatite; concordia diagram
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/gsjgs.156.6.1217

The Connemara region of the western Irish Caledonides records the evolution of a short-lived mid-Ordovician (c. 475-463 Ma) continental magmatic arc that intruded into Dalradian metasedimentary rocks during regional ductile deformation. New U-Pb geochronological data for intermediate intrusive phases and anatexis in southern Connemara are consistent with the relative age succession suggested by field relationships. Calc-alkaline plutons (quartz diorites) were emplaced into the Dalradian sequence and into the Connemara Gabbros at about 467±2 Ma, coeval with anatexis, which was manifested by a 467±2 Ma granitic pegmatite and 468±2 Ma leucosome formation in a metapelite. Metasomatic diopside rocks from west-central Connemara and a calcsilicate rock from southern Connemara yield U-Pb titanite dates of c. 462±2 Ma and 463±2 Ma, respectively. These dates postdate the metamorphic peak by at least five million years and indicate titanite crystallization at a late stage during the metamorphic history. On the basis of U-Pb and 40Ar/39Ar geochronological data we conclude that the cooling history of southern Connemara following anatexis was simple and brief, at a minimum rate of 35°C Ma-1 between 468 and 460 Ma, and 14°C Ma-1 between 460 and 450 Ma.