50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...

deposits), three domes, a lava flow, and plinian
tephra fallout which covered an area of >9000 km 2 .
Three separate rhyolite magmas were involved in
theeruption(T1,T2andT3).T1andT2magmas
are high SiO2 rhyolites, and T3 magma is a low-
SiO2 rhyolite. T1 magma has matrix glass K2Oof 3.43 ± 0.11 (wt.%), whole rock SiO2 of 77.15 ±
0.24 (wt.%), whole rock Sr values of 91 ± 6 (ppm),
orthopyroxene>hornblende mineralogy, Fe-Ti
oxide temperature of 763 ± 12 °C, and oxygen
fugacity (ƒO2) of +0.35 ± 0.12 (NNO). T2 magma
has matrix glass K2O of 4.20 ± 0.09 (wt.%), whole
rock SiO2 of 75.46 ± 0.26 (wt.%), whole rock Sr
values of 122 ± 4 (ppm), biotite>hornblende
mineralogy, temperature of 704 ± 17 °C, and ƒO2 of
-0.45 ± 0.14 (NNO). T1 and T2 magmas are
represented throughout the pyroclastic sequence
and in several domes, and were erupted from the
same vent(s). T3 magma, comprising Western
Dome only, has matrix glass K2O of 3.14 ± 0.06
(wt.%), whole rock SiO2 of 74.12 (wt.%), whole
rock Sr values of 174 (ppm), and hornblendeorthopyroxene
mineralogy. T1 and T2 magmas are
found mingled in some clasts, and a few clasts
contain glass intermediate between the two
compositions. This demonstrates short-lived contact
between the magmas, that were disrupted and
mixing in the conduit during eruption. T3 magma
did not undergo any mixing and was erupted from a
separate vent. The Rerewhakaaitu eruptive event
was triggered by a mafic intrusion, which mixed
with T1 and T2 magmas. Evidence for this includes
mafic micro-blebs (andesitic-dacitic glass
composition) in some rhyolite clasts. These clasts
also contain a disequilibrium crystal assemblage
that includes clinopyroxene and olivine. The
magma dynamics of the Rerewhakaaitu eruption
appears to be broadly similar to that of the 0.7 ka
Kaharoa eruption. Thus, it may be common for
discrete bodies of rhyolite magma to accumulate
beneath Tarawera prior to priming by mafic
intrusion.
POSTER
DUST AS A PROXY FOR CLIMATE
CHANGE: A RECORD OF AUSTRALIAN
DUST DEPOSITION IN NEW ZEALAND
DURING THE HOLOCENE
Samuel K. Marx 1 , Hamish A. McGowan 1
& Balz S. Kamber 2
1 School of Geography, Planning and Architecture,
The University of Queensland, St Lucia, Brisbane,
Qld, 4072, Australia.
2 Department of Earth Sciences, Laurentian
University, Sudbury, Ontario, P3E2C6, Canada.
(s.marx*uq.edu.au)
The aridity of the Australian continent means dust
storms are a common occurrence (McTainsh et al.,
1989), with dust transport to New Zealand reported
on numerous occasions resulting in red coloured
snow and haze (Marx and McGowan, 2005).
Contemporary dust events in Australia are strongly
influenced by environmental conditions within dust
source areas, in particular periods of drought, or
increased windiness, to which dust transport rates
rapidly respond (McTainsh et al., 2005). Therefore,
dust deposition chronologies can be used as an
excellent proxy for palaeoenvironmental
conditions, such as the degree of aridity in dust
source areas and changes in wind strength and dust
transport pathways in response to changing
synoptic circulation patterns.
We present an �8000 year record of Australian dust
deposition extracted from an omobrotrophic peat
bog in Central Otago, New Zealand. Using novel
tertiary and binary trace element mixing models
dust extracted from the bog is provenanced to
specific dust source areas within Australia on a
catchment-geologic scale. Changing rates of dust
deposition, along with the switching on or off of
particular dust source areas within Australian are
thus used to interpret paleoenvironmental
conditions within the region.
Marx, S.K., McGowan, H.A., 2005. A re-examination of
the 1928 trans-Tasman dust transport event. Weather
and Climate, Accepted, 24, 35-55.
McTainsh, G.H., Burgess, R., Pitblado, J.R., 1989.
Aridity, Drought and Dust Storms in Australia (1960-
84). Journal of Arid Environments, 16, 11-22.
McTainsh, G.H., Chan, Y., McGowan, H.A., Leys, J.F.,
Tews, K., 2005. The 23rd October, 2002 dust storm in
eastern Australia: characteristics and meteorological
conditions. Atmospheric Environment, 39, 1227-1236.
ORAL
A 15,000 YEAR RECORD OF SURFACE-
RUPTURING EARTHQUAKES AND FAULT
SLIP AT SAXTON RIVER, AWATERE
FAULT, NEW ZEALAND
D.P.M. Mason 1,2 , T.A. Little 1 &R.J.VanDissen 3
1 School of Earth Sciences, Victoria University of
Wellington, PO Box 600, Wellington
2 Opus International Consultants, PO Box 12003,
Wellington
3 Institute of Geological and Nuclear Sciences, PO
Box 30368, Lower Hutt
(Dougal.Mason*opus.co.nz)
Fault offsets of a well-preserved flight of fluvial
terraces on the Awatere Fault, in northeast South
Island, New Zealand, together with trenching
studies and dating results for late Quaternary
sediments deposited on them, allows the
50 th Kaikoura05 -52- Kaikoura 2005