Zirconolite: A new U-Pb chronometer for mafic igneous rocks

Research Article| September 01, 2004 Zirconolite: A new U-Pb chronometer for mafic igneous rocks Birger Rasmussen; Birger Rasmussen 1School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Ian R. Fletcher Ian R. Fletcher 1School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Geology (2004) 32 (9): 785–788. https://doi.org/10.1130/G20658.1 Article history received: 29 Mar 2004 rev-recd: 24 May 2004 accepted: 26 May 2004 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Birger Rasmussen, Ian R. Fletcher; Zirconolite: A new U-Pb chronometer for mafic igneous rocks. Geology 2004;; 32 (9): 785–788. doi: https://doi.org/10.1130/G20658.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Precise dates for mafic igneous events are essential for tectonic reconstructions and understanding mantle dynamics, mass extinctions, and paleoclimate. Zirconolite (CaZrTi2O7) is a uranium-bearing accessory mineral, found in a wide range of terrestrial and lunar rocks, that has been largely overlooked as a chronometer. In situ U-Pb geochronology of zirconolite from three dolerite intrusions in Western Australia demonstrates that it yields emplacement ages that are more precise than those obtained from coexisting zircon and baddeleyite. Dikes in the Stirling Range Formation give a zirconolite 207Pb/ 206Pb age of 1218 ± 3 Ma, indistinguishable from the less precise dates obtained from zircon (1215 ± 10 Ma) and baddeleyite (1217 ± 39 Ma) and coincident with dike emplacement in the adjacent craton margin and peak metamorphism in the Albany-Fraser orogen. Zirconolite from the 755 Ma Mundine Well dike swarm yields a 207Pb/206Pb age of 754 ± 5 Ma. Sills intruding the Proterozoic Manganese Group contain zirconolite crystals that give a 207Pb/206Pb age of 523 ± 14 Ma. Despite high U contents (550 ppm to 14,000 ppm) and greenschist facies metamorphism, zirconolite in these samples is apparently unaffected by loss of radiogenic Pb. Because of its remarkable properties for U-Pb geochronology, it may soon become the dominant tool for dating mafic igneous rocks as young as 500 Ma by ion microprobe, and thus will prove especially valuable in reconstructing Precambrian geologic history. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.