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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hydrovolcanic eruptions then took place to form the<br />
Mt Bradley Volcaniclastic Member, a low angle<br />
tuff ring formed by both ‘wet’ and ‘dry’ base<br />
surges. ‘Wet’ base surges occurred when there was<br />
excess water supplied at the vent, whereas ‘dry’<br />
base surges occurred when water was limited, or<br />
used in previous eruptions. Magma / water<br />
interaction was shallow, promoting rapid chilling<br />
and fragmentation. Eruption through a shallow<br />
standing body of water is supported by the presence<br />
of middle mud deposits, the majority of blocks over<br />
bombs, preservation of delicate cuspate edges on<br />
glass fragments, large U-shaped channels, and<br />
fluvial deposits and erosion surfaces between<br />
eruptive packages. Hawaiian style eruptive activity<br />
marked the cessation of phreatomagmatic activity,<br />
and formed a thin lava flow. This flow blocked<br />
drainage, allowing the development of a lake, and<br />
formed the upper mud deposits.<br />
A second phase of effusive and phreatomagmatic<br />
activity then occurred, producing the interfingering<br />
Packhorse Lava Member (new name) flows and<br />
Tablelands Volcaniclastic Member. Packhorse Lava<br />
Member flows overcame the topographic controlled<br />
upper sector collapse and flowed further to the<br />
southeast. On exiting the steep sided collapse flows<br />
fanned out, but were constrained to the east by the<br />
growing edifice of Akaroa Volcano. The succession<br />
was then capped by Mt Herbert and flank-fed<br />
Akaroa lava flows.<br />
POSTER<br />
EVOLUTION <strong>OF</strong> THE PALEO-PACIFIC<br />
GONDWANA MARGIN: ISOTOPIC<br />
CONSTRAINTS FROM WEST ANTARCTIC<br />
XENOLITHS<br />
M.R. Handler 1 , R.J. Wysoczanski 1 ,<br />
J.A. Gamble 2 ,V.C.Bennett 3 & J.H. Berg 4<br />
1 Institute for Research on Earth Evolution,<br />
JAMSTEC, Kanagawa 237-0061, Japan<br />
2 Dept of Geology, University College Cork,<br />
Ireland.<br />
3 RSES, Australian National University, Canberra<br />
0200, Australia.<br />
4 Geology & Environmental Geosciences, Northern<br />
Illinois University, USA.<br />
(monica*jamstec.go.jp)<br />
West Antarctica and eastern Australia formed part<br />
of the contiguous Paleo-Pacific Gondwana margin<br />
during Late Proterozoic to Mesozoic times. Key<br />
aspects of the regional evolution of this margin,<br />
including the nature and age of the component<br />
terranes, remain contentious due to the poor<br />
exposure of crustal sequences resulting from the<br />
extensive ice and sedimentary basin cover in West<br />
Antarctica and eastern Australia, respectively.<br />
Samples of the deep crust and lithospheric mantle<br />
are restricted to xenoliths incorporated in the<br />
Cenozoic lavas that have been emplaced along<br />
much of the length of this margin, and which can<br />
preserve unique age and process information that<br />
may be valuable in interpreting continent evolution.<br />
Earlier work in southeastern Australia in particular,<br />
has demonstrated the potential of the Re-Os<br />
isotopic system for constraining the timing of<br />
events recorded in the lithospheric mantle of the<br />
Paleo-Pacific Gondwana margin, with implications<br />
for continent structure and evolution (Handler and<br />
Bennett, 2001).<br />
We will present new Os and Nd isotopic data for<br />
lithospheric xenoliths from Marie Byrd Land and<br />
Victoria Land, Antarctica, together with previously<br />
published Re-Os data and model ages from along<br />
the PaleoPacific Gondwana margin in southeastern<br />
Australia and central Marie Byrd Land (McBride et<br />
al., 1996; Handler and Bennett, 2001; Handler et<br />
al., 2003), and discuss their implications for the<br />
development of the margin. The results suggest<br />
preservation of Proterozoic lithospheric mantle<br />
along the sampled length of the margin. Striking<br />
observations include: the similarity of the oldest<br />
PaleoProterozoic Os model ages found beneath the<br />
Delamerian Fold Belt of southeastern Australia and<br />
beneath West Antarctica; preservation of a ca. 500<br />
Ma age from central Marie Byrd Land; and the<br />
suggestion that a significant melting event may<br />
have affected the mantle beneath both southeast<br />
Australia and Marie Byrd Land ca. 900 – 1100 Ma.<br />
The timing of this speculated MesoProterozoic<br />
mantle event(s) coincides with the age of a<br />
significant peak in the U-Pb detrital zircon age<br />
spectra of the vast turbidite deposits of the Paleo-<br />
Pacific Gondwana margin (Wysoczanski and<br />
Allibone, 2004).<br />
Handler MR and Bennett VC (2001) Tectonics 20: 177-<br />
188.<br />
Handler MR, Wysoczanski RJ and Gamble JA (2003)<br />
Chemical Geology 196: 131-145.<br />
McBride JS, Lambert DD, Greig A and Nicholls IA<br />
(1996) Geology 24: 631-634.<br />
Wysoczanski RJ and Allibone, AH (2004) Journal of<br />
Geology 112: 401-416.<br />
ORAL<br />
50 th <strong>Kaikoura</strong>05 -33- <strong>Kaikoura</strong> <strong>2005</strong>