SHRIMP U-Pb dating of the preeruption growth history of zircons from the 340 ka Whakamaru Ignimbrite, New Zealand: Evidence for >250 k.y. magma residence times

Abstract

Research Article| November 01, 1999 SHRIMP U-Pb dating of the preeruption growth history of zircons from the 340 ka Whakamaru Ignimbrite, New Zealand: Evidence for >250 k.y. magma residence times Stuart J. A. Brown; Stuart J. A. Brown 1Centre for Teaching and Research in Strategic Mineral Deposits, Department of Geology and Geophysics, University of Western Australia, Nedlands 6907, Western Australia, Australia Search for other works by this author on: GSW Google Scholar Ian R. Fletcher Ian R. Fletcher 1Centre for Teaching and Research in Strategic Mineral Deposits, Department of Geology and Geophysics, University of Western Australia, Nedlands 6907, Western Australia, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Stuart J. A. Brown 1Centre for Teaching and Research in Strategic Mineral Deposits, Department of Geology and Geophysics, University of Western Australia, Nedlands 6907, Western Australia, Australia Ian R. Fletcher 1Centre for Teaching and Research in Strategic Mineral Deposits, Department of Geology and Geophysics, University of Western Australia, Nedlands 6907, Western Australia, Australia Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1999) 27 (11): 1035–1038. https://doi.org/10.1130/0091-7613(1999)027<1035:SUPDOT>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Stuart J. A. Brown, Ian R. Fletcher; SHRIMP U-Pb dating of the preeruption growth history of zircons from the 340 ka Whakamaru Ignimbrite, New Zealand: Evidence for >250 k.y. magma residence times. Geology 1999;; 27 (11): 1035–1038. doi: https://doi.org/10.1130/0091-7613(1999)027<1035:SUPDOT>2.3.CO;2 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 The Whakamaru group ignimbrites are products of one of the largest caldera-forming eruptions from the central Taupo Volcanic Zone, New Zealand, ca. 340 ka. Imaging of zircons separated from low-silica rhyolite pumice from Whakamaru group ignimbrite reveals a complex magmatic crystallization history; some grains contain resorbed cores. Cores and rims of individual zircons were dated using the sensitive high-resolution ion microprobe. Due to the high U contents of the zircons, 206Pb count rates were sufficiently high to obtain 206Pb/238U ages with precisions of 5%–10% (1 σS) using longer than usual 206Pb+ count times, and this has allowed zircon core and rim ages to be distinguished. Zircon rim and outer growth zone ages range from within 1 σS error of the eruption age to 449 ± 20 ka, whereas zircon cores produced ages to 608 ± 20 ka, indicating magmatic residence times exceeding 250 k.y. for some zircons. The data are consistent with a prolonged evolution of the magma system over hundreds of thousands of years, involving magma replenishment and mixing with residual phases of older silicic magma chambers, in addition to crystal fractionation processes, prior to eruption. The study has shown that 206Pb/238U dating using high-resolution ion microprobe can be used to determine zircon preeruptive growth histories in Quaternary lavas and pyroclastic rocks. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.