50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
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deposits), three domes, a lava flow, and plinian<br />
tephra fallout which covered an area of >9000 km 2 .<br />
Three separate rhyolite magmas were involved in<br />
theeruption(T1,T2andT3).T1andT2magmas<br />
are high SiO2 rhyolites, and T3 magma is a low-<br />
SiO2 rhyolite. T1 magma has matrix glass K2Oof 3.43 ± 0.11 (wt.%), whole rock SiO2 of 77.15 ±<br />
0.24 (wt.%), whole rock Sr values of 91 ± 6 (ppm),<br />
orthopyroxene>hornblende mineralogy, Fe-Ti<br />
oxide temperature of 763 ± 12 °C, and oxygen<br />
fugacity (ƒO2) of +0.35 ± 0.12 (NNO). T2 magma<br />
has matrix glass K2O of 4.20 ± 0.09 (wt.%), whole<br />
rock SiO2 of 75.46 ± 0.26 (wt.%), whole rock Sr<br />
values of 122 ± 4 (ppm), biotite>hornblende<br />
mineralogy, temperature of 704 ± 17 °C, and ƒO2 of<br />
-0.45 ± 0.14 (NNO). T1 and T2 magmas are<br />
represented throughout the pyroclastic sequence<br />
and in several domes, and were erupted from the<br />
same vent(s). T3 magma, comprising Western<br />
Dome only, has matrix glass K2O of 3.14 ± 0.06<br />
(wt.%), whole rock SiO2 of 74.12 (wt.%), whole<br />
rock Sr values of 174 (ppm), and hornblendeorthopyroxene<br />
mineralogy. T1 and T2 magmas are<br />
found mingled in some clasts, and a few clasts<br />
contain glass intermediate between the two<br />
compositions. This demonstrates short-lived contact<br />
between the magmas, that were disrupted and<br />
mixing in the conduit during eruption. T3 magma<br />
did not undergo any mixing and was erupted from a<br />
separate vent. The Rerewhakaaitu eruptive event<br />
was triggered by a mafic intrusion, which mixed<br />
with T1 and T2 magmas. Evidence for this includes<br />
mafic micro-blebs (andesitic-dacitic glass<br />
composition) in some rhyolite clasts. These clasts<br />
also contain a disequilibrium crystal assemblage<br />
that includes clinopyroxene and olivine. The<br />
magma dynamics of the Rerewhakaaitu eruption<br />
appears to be broadly similar to that of the 0.7 ka<br />
Kaharoa eruption. Thus, it may be common for<br />
discrete bodies of rhyolite magma to accumulate<br />
beneath Tarawera prior to priming by mafic<br />
intrusion.<br />
POSTER<br />
DUST AS A PROXY FOR CLIMATE<br />
CHANGE: A RECORD <strong>OF</strong> AUSTRALIAN<br />
DUST DEPOSITION IN <strong>NEW</strong> ZEALAND<br />
DURING THE HOLOCENE<br />
Samuel K. Marx 1 , Hamish A. McGowan 1<br />
& Balz S. Kamber 2<br />
1 School of Geography, Planning and Architecture,<br />
The University of Queensland, St Lucia, Brisbane,<br />
Qld, 4072, Australia.<br />
2 Department of Earth Sciences, Laurentian<br />
University, Sudbury, Ontario, P3E2C6, Canada.<br />
(s.marx*uq.edu.au)<br />
The aridity of the Australian continent means dust<br />
storms are a common occurrence (McTainsh et al.,<br />
1989), with dust transport to New Zealand reported<br />
on numerous occasions resulting in red coloured<br />
snow and haze (Marx and McGowan, <strong>2005</strong>).<br />
Contemporary dust events in Australia are strongly<br />
influenced by environmental conditions within dust<br />
source areas, in particular periods of drought, or<br />
increased windiness, to which dust transport rates<br />
rapidly respond (McTainsh et al., <strong>2005</strong>). Therefore,<br />
dust deposition chronologies can be used as an<br />
excellent proxy for palaeoenvironmental<br />
conditions, such as the degree of aridity in dust<br />
source areas and changes in wind strength and dust<br />
transport pathways in response to changing<br />
synoptic circulation patterns.<br />
We present an �8000 year record of Australian dust<br />
deposition extracted from an omobrotrophic peat<br />
bog in Central Otago, New Zealand. Using novel<br />
tertiary and binary trace element mixing models<br />
dust extracted from the bog is provenanced to<br />
specific dust source areas within Australia on a<br />
catchment-geologic scale. Changing rates of dust<br />
deposition, along with the switching on or off of<br />
particular dust source areas within Australian are<br />
thus used to interpret paleoenvironmental<br />
conditions within the region.<br />
Marx, S.K., McGowan, H.A., <strong>2005</strong>. A re-examination of<br />
the 1928 trans-Tasman dust transport event. Weather<br />
and Climate, Accepted, 24, 35-55.<br />
McTainsh, G.H., Burgess, R., Pitblado, J.R., 1989.<br />
Aridity, Drought and Dust Storms in Australia (1960-<br />
84). Journal of Arid Environments, 16, 11-22.<br />
McTainsh, G.H., Chan, Y., McGowan, H.A., Leys, J.F.,<br />
Tews, K., <strong>2005</strong>. The 23rd October, 2002 dust storm in<br />
eastern Australia: characteristics and meteorological<br />
conditions. Atmospheric Environment, 39, 1227-1236.<br />
ORAL<br />
A 15,000 YEAR RECORD <strong>OF</strong> SURFACE-<br />
RUPTURING EARTHQUAKES AND FAULT<br />
SLIP AT SAXTON RIVER, AWATERE<br />
FAULT, <strong>NEW</strong> ZEALAND<br />
D.P.M. Mason 1,2 , T.A. Little 1 &R.J.VanDissen 3<br />
1 School of Earth Sciences, Victoria University of<br />
Wellington, PO Box 600, Wellington<br />
2 Opus International Consultants, PO Box 12003,<br />
Wellington<br />
3 Institute of Geological and Nuclear Sciences, PO<br />
Box 30368, Lower Hutt<br />
(Dougal.Mason*opus.co.nz)<br />
Fault offsets of a well-preserved flight of fluvial<br />
terraces on the Awatere Fault, in northeast South<br />
Island, New Zealand, together with trenching<br />
studies and dating results for late Quaternary<br />
sediments deposited on them, allows the<br />
50 th <strong>Kaikoura</strong>05 -52- <strong>Kaikoura</strong> <strong>2005</strong>