Untitled Document
Preliminary zircon U-Pb dating of late Paleozoic granites
across the boundary between the Lachlan and New England fold belts
Heejin Jeon, Ian Williams and Vickie Bennett
1 Research School of Earth Sciences, Australian National University, Canberra,
ACT 0200, Australia
Figure 1. Typical feature of Bathurst and Gulgong batholiths that
contain big pink feldspar crystals.
Lachlan and New England fold belts are major tectonic components of
eastern Australia. Because the boundary between them is totally covered
by the huge Sydney basin, their tectonic relationship is unclear. However,
the Carboniferous granites in the north-eastern Lachlan Fold Belt show
similarities in age and composition with granites (Chappell et al., 1988)
and volcanics (Shaw and Flood, 1993) in the New England Fold Belt. Based
on these data, we could infer that the two fold belts might share the
same basement and lower crustal structure. Therefore, our purpose is
to trace the geologic history and decipher their relationship under the
crust through the signature recorded in similar aged granites (Carboniferous
to Permian) across the boundary between the Lachlan and New England fold
belts. The combination of in situ U/Pb - O - Hf isotopic data for zircon
will be a key for this study (e.g., Kemp et al., 2007).
Although a large amount of isotopic work on the granites of the Lachlan
Fold Belt has been done over 30 years, there is little published work
for the Carboniferous granites. Zircon from the Oberon, Bathurst and
Gulgong batholiths has been dated. The ages of the granites dated so
far range from ~340 to ~330 Ma. There is no simple age trend north to
south, but the granites immediately west of Lithgow do appear to become
younger from west to east.
Zircon has also been studied from the Banalasta (~290 Ma) and Inlet (~250
Ma) granites of the Bundarra and Moonbi supersuites, respectively, in
the New England Fold Belt. Zircons of Banalasta show Carboniferous cores
around 330 Ma old, while those of Inlet have no old cores at all. These
preliminary results are not enough to conclude, but a beautiful story
would be envisaged soon because O and Hf isotopic analyses for dated
zircon grains are in progress now.
Shaw, S.E. and Flood, R.H., 1993. Carboniferous magmatic activity
in the Lachlan and New England Fold Belts. In: Flood P.G. & Aitchison
J.C. eds. New England Orogen eastern Australia NEO'93 Conference, pp.
113-121. University of New England, Armidale.
Kemp, A.I.S., Hawkesworth, C.J., Foster, G.L., Paterson, B.A., Woodhead,
J.D., Hergt, J.M., Gray, C.M. and Whitehouse, M.J., 2007, Magmatic and
Crustal Differentiation History of Granitic Rocks from Hf-O Isotopes
in Zircon, Science, 315: 980-983.
Chappell, B.W., White, A.J.R., and Hine, R., 1988, Granite provinces
and basement terranes in the Lachlan Fold Belt, southeastern Australia,
Australian Journal of Earth Sciences, 35, 505-521.