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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large volumes of A-type magmatism in Queensland<br />
may shed light on the significance of its apparently<br />
rare equivalent in NZ. Thus A-type magmatism at<br />
~130 Ma in NZ may explain the sudden major<br />
HiSY flux as being due to heat associated with an<br />
otherwise largely unrecognised incursion of<br />
asthenospheric mantle-derived magmas, probably<br />
by slab rifting or roll back. In Queensland, by<br />
analogy, the “extension-related” magmatism may<br />
also have been “intra-arc”, rather than strictly<br />
intracontinental.<br />
ORAL<br />
PROGRESS ON QMAP FIORDLAND<br />
Turnbull 1 , A. Allibone 2 , R. Jongens 1 ,<br />
H. Fraser 1 ,A.Tulloch 1<br />
1 Institute of Geological and Nuclear Sciences,<br />
Private Bag 1930, Dunedin<br />
2 School of Earth Science, James Cook University,<br />
Townsville, Q4811, Australia<br />
(i.turnbull*gns.cri.nz)<br />
Work on the Fiordland QMAP sheet has been under<br />
way for four field seasons with the southern twothirds<br />
of Fiordland now largely mapped. Some of<br />
the more significant findings of the work to date are<br />
highlighted on this poster.<br />
Schistose amphibolite facies metasediments,<br />
previously interpreted as the upper plate of a<br />
Western Fiordland Block, are now known to extend<br />
as far south as Chalky Inlet rather than terminating<br />
in Dusky Sound. These metasediments, and several<br />
younger granitoid units, strike across the mouth of<br />
Dusky Sound and indicate that the Dusky Fault<br />
does not extend out to sea as previously postulated.<br />
Movement is instead accommodated on a major<br />
SW-trending fault that crosses the coast near West<br />
Cape; consequently the Dusky Fault, previously<br />
thought to separate distinct Western and Southern<br />
Fiordland Blocks, appears to be of local rather than<br />
regional importance. Ordovician graptolitic shales<br />
and interbedded sandstone and quartzite previously<br />
included in a Southern Fiordland Block, as well as<br />
the schistose amphibolite facies rocks, are intruded<br />
by the Brothers and c. 350 Ma Evans Plutons,<br />
indicating that they have been in close proximity<br />
since the mid Paleozoic.<br />
The c. 30+ granitoid plutons mapped show regional<br />
variations in composition and age across southern<br />
Fiordland. Carboniferous plutons are largely<br />
confined to the area between Dusky Sound and the<br />
Princess Mountains, and include at least 3 distinct<br />
groups, one of which correlates with the Ridge<br />
Orthogneiss on Stewart Island. Gabbroic, dioritic<br />
and related LoSY granodioritic rocks, c. 170-140<br />
Ma old, similar to those mapped in northern<br />
Stewart Island and northeastern Fiordland, form a<br />
belt of heterogeneous variably deformed intrusions<br />
that extends from northeast of Lake Manapouri to<br />
the Princess Mountains. The presence of the c. 164<br />
Ma Lake Mike Granite in SW Fiordland indicates<br />
this Jurassic plutonism locally extended further<br />
west. Younger HiSY plutons, correlated with the<br />
Separation Point Suite, form a narrow belt<br />
extending south from the western side of Lake<br />
Manapouri to Lake Poteriteri. Elsewhere in<br />
southern Fiordland, Cretaceous HiSY rocks are<br />
restricted to isolated plutons in the eastern Hunter<br />
Mountains and south of Dusky Sound. Numerous<br />
LoSY tonalitic to leucogranitic plutons, some dated<br />
at c. 130-135 Ma, occur in SW Fiordland; their<br />
affinity with other documented suites is not yet<br />
clear.<br />
Cretaceous and Cenozoic sedimentary rocks had<br />
generally been mapped and described prior to the<br />
QMAP programme. However, newly discovered<br />
fossiliferous Pleistocene sediments that fill a<br />
submarine canyon east of Puysegur Point give<br />
valuable control on tectonic uplift rates for flights<br />
of marine terraces in SW Fiordland.<br />
The Grebe Shear Zone, previously interpreted as<br />
the boundary between Eastern and Southern<br />
Fiordland Blocks, is cut by probably Early<br />
Cretaceous (Separation Point Suite) granitoids,<br />
implying correlation with the Gutter Shear Zone on<br />
Stewart Island. Innumerable brittle faults have been<br />
mapped; some offset the contacts of the Western<br />
Fiordland Orthogneiss. Demonstrable Late<br />
Quaternary faulting is rare.<br />
POSTER<br />
WORKING TOWARD A HIGH-PRECISION<br />
RECORD <strong>OF</strong> MT TARANAKI ERUPTIONS<br />
AND ASH FALLS, <strong>NEW</strong> ZEALAND<br />
M. Turner 1 , S. Cronin 1 ,M.Bebbington 2 ,<br />
B. Stewart 1 ,V.Neall 1 and I. Smith 3<br />
1 Institute of Natural Resources, Massey University,<br />
Palmerston North, New Zealand<br />
2 Institute of Information Sciences and Technology,<br />
Massey University, Palmerston North, New<br />
Zealand<br />
3 Department of Geology, University of Auckland,<br />
Auckland, New Zealand<br />
(M.B.Turner*massey.ac.nz)<br />
A probabilistic assessment of eruption recurrence at<br />
any volcano requires quantification of the<br />
frequency and magnitude of each style of possible<br />
volcanic hazard. Existing eruption age data for<br />
frequency analysis at Taranaki is, as for many<br />
volcanoes, poorly constrained and relies on a few<br />
radiocarbon dates from widely distributed<br />
stratigraphic sections on and around the volcano.<br />
We have extracted what seems to be the highest<br />
resolution record yet of Taranaki volcanism from<br />
peaty lacustrine sediments within a small lake,<br />
50 th <strong>Kaikoura</strong>05 -90- <strong>Kaikoura</strong> <strong>2005</strong>