Uranium-lead isotopic ages of plagiogranites from the Troodos Ophiolite, Cyprus, and their tectonic significance

• Published in: Geology (Boulder) 1987-09, Vol.15 (9), p.825-828
• Main Authors: Mukasa, Samuel B, Ludden, John N
• Format: Article
• Language: English
• Subjects: absolute age; Asia; Cretaceous; Cyprus; dates; diorites; emplacement; geochronology; Geophysics; igneous and metamorphic rocks; igneous rocks; intrusions; magmas; Mesozoic; Middle East; nesosilicates; ophiolite; orthosilicates; Petrology; plagiogranite; plate tectonics; plutonic rocks; plutons; Radiolaria; silicates; solid Earth (tectonophysics); Troodos Massif; U/Pb; ultramafics; Upper Cretaceous; zircon; zircon group
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/0091-7613(1987)15<825:UIAOPF>2.0.CO;2

The plagiogranites occur at the top of the intrusive section of the Troodos ophiolite and represent fractional residua of magma chambers related to the lower pillow lavas. They are possibly slightly older than small ultramafic layered complexes that represent the final intrusive episode within the Troodos ophiolite. A bulk zircon population from a dioritic plagiogranite yielded slightly discordant zircon U/Pb dates of 90.3(0.7) and 92.1(0.7) m.y. Another group from a leucocratic plagiogranite gave a concordant U/Pb crystallization age of 91.1(0.7) to 92.4(0.7) m.y. and an average of 91.6(1.4) m.y. These ages are slightly lower than U/Pb zircon ages from the Samail ophiolite in Oman, which vary 93.5-97.9 m.y. and average 95 m.y. The small difference in age between the Troodos and the Samail ophiolites and the geochemical similarities of basalts from both complexes to island-arc volcanics imply that a 3000-km axis of rift-related island arc formed between 91 and 98 m.y. ago. Emplacement of the ophiolites followed during the early Maastrichtian.