Age of the Auckland Volcanic Field Jan Lindsay and Graham Leonard
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Age of the Auckland Volcanic Field Jan Lindsay and Graham Leonard IESE Report 1-2009.02 | June 2009 ISBN: [print] 978-0-473-15316-8 [PDF] 978-0-473-15416-5 Age of the Auckland Volcanic Field Jan Lindsay1 and Graham Leonard2 1School of Environment & Institute of Earth Science and Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand; [email protected] 2GNS Science, PO Box 30368, Lower Hutt 5040 New Zealand; [email protected] IESE Report 1-2009.02 | June 2009 ISBN: [print] 978-0-473-15316-8 [PDF] 978-0-473-15416-5 This report was prepared by IESE as part of the DEVORA Project. Disclaimer: While the information contained in this report is believed to be correct at the time of publication, the Institute of Earth Science and Engineering and its working parties and agents involved in preparation and publication, do not accept any liability for its contents or for any consequences arising from its use. Copyright: This work is copyright of the Institute of Earth Science and Engineering. The content may be used with acknowledgement to the Institute of Earth Science and Engineering and the appropriate citation. TABLE OF CONTENTS INTRODUCTION .......................................................................................................................... 2 Project objectives ..................................................................................................................... 2 Methodology ............................................................................................................................. 3 Geological framework ............................................................................................................... 3 DATING TECHNIQUES USED IN THE AUCKLAND VOLCANIC FIELD .................................... 5 Radiocarbon dating .............................................................................................................. 5 K-Ar dating ........................................................................................................................... 6 40Ar/39Ar dating ..................................................................................................................... 6 Paleomagnetic declination ................................................................................................... 6 Optically stimulated luminescence dating............................................................................. 6 Thermoluminescence dating ................................................................................................ 7 REVIEW OF AGES ...................................................................................................................... 7 THE AGE OF INDIVIDUAL CENTRES OF THE AVF ................................................................ 11 Ash Hill ................................................................................................................................... 11 Auckland Domain ................................................................................................................... 11 Crater Hill tuff ring .................................................................................................................. 11 Green Hill ............................................................................................................................... 11 Hampton Park ........................................................................................................................ 12 Mangere Mountain ................................................................................................................. 13 Matakarua/McLaughlin’s Hill................................................................................................... 13 Maungataketake/Ihumatao ..................................................................................................... 13 McLennan Hills ....................................................................................................................... 15 Mount Albert ........................................................................................................................... 15 Mount Eden ............................................................................................................................ 16 Mount Richmond .................................................................................................................... 16 Mount Saint John ................................................................................................................... 16 Mount Wellington (Maungarei) ............................................................................................... 17 One Tree Hill .......................................................................................................................... 18 Onepoto .................................................................................................................................. 19 Otuataua ................................................................................................................................. 19 Panmure Basin tuff ring .......................................................................................................... 19 Pukeiti ..................................................................................................................................... 20 Puketutu Island ....................................................................................................................... 20 Pupuke ................................................................................................................................... 21 Purchas Hill ............................................................................................................................ 21 Rangitoto ................................................................................................................................ 22 Age of the first Rangitoto eruption ...................................................................................... 23 Age of the second Rangitoto eruption ................................................................................ 23 Best estimate age for Rangitoto ......................................................................................... 25 Three Kings ............................................................................................................................ 25 Wiri Mountain/Manurewa ........................................................................................................ 27 DISCUSSION ............................................................................................................................. 27 Best estimate ages for AVF volcanoes .................................................................................. 27 Frequency of past activity in the AVF ..................................................................................... 31 Correlation of tephra layers in cores with volcanic vents ........................................................ 32 Implications for hazard assessment and hazard models ........................................................ 32 RECOMMENDATIONS FOR FUTURE WORK .......................................................................... 33 REFERENCES ........................................................................................................................... 34 ACKNOWLEDGEMENTS .......................................................................................................... 38 APPENDIX 1: Database of radiometric ages for the Auckland Volcanic Field ........................... 39 INTRODUCTION In 2008 a multi-disciplinary research programme was launched, a GNS Science – University of Auckland collaboration with the aim of DEtermining VOlcanic Risk in Auckland (DEVORA). A major aspiration of DEVORA is development of a probabilistic hazard model for the Auckland Volcanic Field (AVF). This will be achieved by investigating past eruption magnitude-frequency relationships and comparing these with similar data from analogous volcanic fields. A key data set underpinning this is an age database for the AVF. To this end a comprehensive dating campaign is planned as part of DEVORA. This report, Age of the Auckland Volcanic Field, is a synthesis of all currently available age data for the AVF. It represents one of several reports carried out as part of the ‘synthesis’ phase of DEVORA, whereby existing data from all previous work is collated and summarised, so that gaps in current knowledge can be identified and addressed. PROJECT OBJECTIVES Determining eruption magnitude-frequency relationships in volcanic regions is a critical first step in assessing volcanic hazard (e.g. Condit and Connor 1996; Conway et al. 1998; Connor et al. 2006). Such analysis has been hampered in the AVF due to a lack of reliable age data. Carbonised material is rare and many centres are older than 40,000 years, thus limiting the use of 14C dating. Early attempts to date Auckland lavas using the K-Ar technique revealed excess Ar, making the lavas appear older than they are (e.g. McDougall et al. 1969). The tephra record obtained from drilling the paleolake sediments of Auckland’s maars is providing excellent interpolated ages for basaltic AVF tephras. However, as yet only a few tephras retrieved from these cores have been reliably correlated to individual centres (e.g. Rangitoto tephra in Pupuke core; Crater Hill tephra