HR: 1340h
AN: V53B-1549    [Abstracts]
TI: The 340-240 ka Ignimbrite Flare-up Event in Taupo Volcanic Zone, New Zealand
AU: * Wilson, C J
EM: cjn.wilson@auckland.ac.nz
AF: Dept of Geology University of Auckland, PB 92019, Auckland, 1020 New Zealand
AU: Gravley, D M
EM: d.gravley@auckland.ac.nz
AF: Dept of Geology University of Auckland, PB 92019, Auckland, 1020 New Zealand
AU: Leonard, G S
EM: g.leonard@gns.cri.nz
AF: IGNS, PO Box 30368, Lower Hutt, 6315 New Zealand
AU: Charlier, B L
EM: b.l.a.charlier@open.ac.uk
AF: Dept of Earth Sciences Open University, Walton Hall, Milton Keynes, MK7 6AA United Kingdom
AU: Rowland, J V
EM: j.rowland@auckland.ac.nz
AF: Dept of Geology University of Auckland, PB 92019, Auckland, 1020 New Zealand
AU: Machado, H B
EM: hugomachado@net.sapo.pt
AF: Dept Geological Sciences University of Canterbury, PB 4800, Christchurch, 0000 New Zealand
AU: Cole, J W
EM: jim.cole@canterbury.ac.nz
AF: Dept Geological Sciences University of Canterbury, PB 4800, Christchurch, 0000 New Zealand
AB: The onset of continental rifting often sees outbursts of intensive silicic volcanism - ignimbrite flare-up events - with complex relationships between extensional, magmatic and volcanic processes. The central Taupo Volcanic Zone (TVZ) in New Zealand is a young vigorously active silicic focus in a rifting arc setting. Much of the present-day character of central TVZ was established in a remarkable flare-up event from ~340 to ~240 ka. At this time ≥7 ignimbrite-forming and numerous smaller eruptions occurred, totaling at least 1700 and probably 3000 km³ of magma, and forming calderas that pepper a 90 × 40 km area. The first and largest event(s) generated the Whakamaru-group ignimbrites and their coeruptive fall deposits, and these were followed by a modest-sized ignimbrite (Chimp) prior to 280 ka. Two ignimbrites were emplaced west (Pokai) and east (Matahina) of TVZ at ~280 ka, and three ignimbrites were erupted around ~240 ka: of these one (Kaingaroa) is distributed east and two (Mamaku and Ohakuri) west of TVZ. These last two ignimbrites closed the flare-up event. However, the parental eruptions occurred from vents centered 35 km apart, but formed a complex overlapping eruption sequence. Early wet and dry pumice fall deposits from a southerly (`Ohakuri'?) source underlie, and are coeval with, flow units of the Mamaku ignimbrite from a northerly source now expressed as Rotorua caldera. A fine-grained coignimbrite ash bed was then deposited on both fall and flow deposits. This ash bed was then only minimally disturbed by erosion before eruption of the Ohakuri ignimbrite from the southerly source. Such close temporal linkages between major eruptions imply that faulting readjustment was critical in triggering neighboring events. Future work is aimed at reconstructing the magma bodies for the flare-up ignimbrites to see to what extent their crystallization histories overlapped in time, and what degree of commonality in chemical and isotopic characteristics there was between roughly to closely coeval but spatially separated large magma bodies.
DE: 1065 Major and trace element geochemistry
DE: 1090 Field relationships (3690, 8486)
DE: 8428 Explosive volcanism
DE: 8440 Calderas
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005