Zircon Dating and
Provenance of Rhyolitic Clasts in Beacon Conglomerate, Southern
Victoria Land, Antarctica
R.J. Wysoczanski1, P.J. Forsyth2*
& K.J. Woolfe3
1Research School of
Earth Sciences, The Australian National University, Canberra ACT0200 -
Australia
and IFREE, Japan Marine Science and Technology Center, Yokosuka
237-0061 - Japan
2Institute of Geological and Nuclear Sciences, Private Bag
1930, Dunedin - New Zealand
3formerly James Cook University, Townsville, Queensland –
Australia
Received 5 June 2003; accepted in revised form 15 September 2003
Abstract
- Pebbles from Sperm Bluff Conglomerate (Taylor Group, Beacon
Supergroup) include lithologies such as porphyritic rhyolites and tuffs
that are not known in outcrop anywhere in southern Victoria Land.
Zircon from the clasts yielded ages between 497 ± 17 Ma and 482
± 9 Ma, with an older inherited component c. 540 Ma. The age and composition
of the rhyolites and tuffs suggest that they are the shallow
equivalents of Dry Valleys (DV) 2 suite granitoids from a local source,
or a source with felsic magmatism of similar age to the DV2 suite. The
best constrained ages show that rhyolitic volcanism occurred in the
source region at c. 482
± 9 to 484 ± 8 Ma, towards the end of Dry Valleys
magmatism, while older zircon grains were formed at the same time as
early phases of Dry Valleys magmatism. The ability of U-Pb ages of
robust minerals such as zircon, to allow correlations of rocks that
have been extensively altered, highlights the value of this technique
(and particularly SHRIMP) in providing important geological constraints
on altered rocks.
*Corresponding author (j.forsyth@gns.cri.nz)