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.