A multiple-approach radiometric age estimate for the Rotoiti and Earthquake Flat eruptions,New Zealand,with implications for the MIS 4/3 boundary |
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| Institution: | 1. Centro de Geociencias, Universidad Nacional Autónoma de México, Blvd. Juriquilla, 3001, 76230, Juriquilla, Querétaro, Mexico;2. RISKNAT Group, Geomodels Institute, Earth and Ocean Dynamics Department, Universitat de Barcelona, C/ Martí i Franquès s/n, 08028 Barcelona, Spain;3. Institut des Sciences de la Terre, ISTerre, IRD, Université Joseph Fourier, Grenoble I, OSUG, France;4. Barcelona-CSI, Institut de Ciències del Mar - CSIC, CMIMA, Psg. Martim de la Barceloneta, 37-49, 08003 Barcelona, Spain;5. GRD, Scripps Institution of Oceanography, University of California San Diego, La Jolla 92093, USA;6. Institut de Radioprotection et Sûreté Nucléaire (IRSN), BP 17, 92262 Fontenay-aux-Roses, France;1. School of Geography, Environment and Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand;2. School of Environment, University of Auckland, Auckland, New Zealand;3. National Oceanography Centre, University of Southampton Waterfront Campus, Southampton, SO14 3ZH, United Kingdom;4. National Institute of Water and Atmospheric Research, Wellington, New Zealand |
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| Abstract: | Pyroclastic fall deposits of the paired Rotoiti and Earthquake Flat eruptions from the Taupo Volcanic Zone (New Zealand) combine to form a widespread isochronous horizon over much of northern New Zealand and the southwest Pacific. This horizon is important for correlating climatic and environmental changes during the Last Glacial period, but has been the subject of numerous disparate age estimates between 35.1±2.8 and 71±6 ka (all errors are 1 s.d.), obtained by a variety of techniques. A potassium–argon (K–Ar) age of 64±4 ka was previously determined on bracketing lavas at Mayor Island volcano, offshore from the Taupo Volcanic Zone. We present a new, more-precise 40Ar/39Ar age determination on a lava flow on Mayor Island, that shortly post-dates the Rotoiti/Earthquake Flat fall deposits, of 58.5±1.1 ka. This value, coupled with existing ages from underlying lavas, yield a new estimate for the age of the combined eruptions of 61.0±1.4 ka, which is consistent with U–Th disequilibrium model-age data for zircons from the Rotoiti deposits. Direct 40Ar/39Ar age determinations of plagioclase and biotite from the Rotoiti and Earthquake Flat eruption products yield variable values between 49.6±2.8 and 125.3±10.0 ka, with the scatter attributed to low radiogenic Ar yields, and/or alteration, and/or inheritance of xenocrystic material with inherited Ar. Rotoiti/Earthquake Flat fall deposits occur in New Zealand in association with palynological indicators of mild climate, attributed to Marine Isotope Stage (MIS) 3 and thus used to suggest an age that is post-59 ka. The natures of the criteria used to define the MIS 4/3 boundary in the Northern and Southern hemispheres, however, imply that the new 61 ka age for the Rotoiti/Earthquake Flat eruption deposits will provide the inverse, namely, a more accurate isochronous marker for correlating diverse changes across the MIS 4/3 boundary in the southwest Pacific. |
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