High-temperature–low-pressure metamorphism and the production of S-type granites of the Hillgrove Supersuite, southern New England Orogen, NSW, Australia

ABSTRACT

The high-temperature–low-pressure Wongwibinda Metamorphic Complex of the southern New England Orogen is bound by S-type granite plutons of the Hillgrove Supersuite to the north, east and south. New U–Pb geochronology of five samples of the Hillgrove Supersuite demonstrates that plutonism in the complex involved two pulses: ca 300 Ma and ca 292 Ma. This indicates that plutonism partially overlaps the age of high-T–low-P metamorphism (296.8 ± 1.5 Ma), but also postdates it. Zircon grains identified as xenocrysts based on age (≥310 Ma) have U–Pb–Hf isotopic character that largely overlaps detrital grains in the host Girrakool Beds, indicating that accretionary complex crust is the likely source of these xenocrysts. The ¹⁷⁶Hf/¹⁷⁷Hf initial character for zircon for the ca 300 Ma plutons (three samples) is less radiogenic than those in the ca 292 Ma plutons (two samples). The progression in ¹⁷⁶Hf/¹⁷⁷Hf initial character for zircon infers an increasing mantle component in the Hillgrove Supersuite with time. These data are evidence of a rift tectonic setting, where mantle-derived magmas are predicted to more readily migrate to shallower crustal levels as the crust thins and becomes hotter. Additionally, early episodes of partial melting in the system melt-depleted the metasedimentary sources, thus reducing the S-type component as anatexis progressed. The evolution of the Hillgrove Supersuite coincides with a period of early Permian slab roll back and extension accompanied by crustal rifting and thinning, leading to high-T–low-P metamorphism, anatexis and S-type granite production and the development of rift basins such as the Sydney–Gunnedah–Bowen system.

KEYWORDS:

• zircon U–Pb–Hf
• Wongwibinda Metamorphic Complex
• accretionary wedge
• New England Orogen
• S-type granite
• high-temperature–low-pressure metamorphism

Acknowledgements

Macquarie University Research Development Grant funding to NRD provided financial support to conduct this research. We thank the local landowners for permission to visit and sample localities in the Wongwibinda Metamorphic Complex. P. A. Cawood, T. Raimondo and G. Rosenbaum are thanked for comments made on a thesis chapter version of this research. Critical reviews by Peter Cawood and Bill Landenberger are appreciated. The analytical data were obtained using instrumentation funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS/AuScope, industry partners and Macquarie University. This is contribution 1042 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1195 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au/).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary papers

Table A1. U–Pb isotope data.

Table A2. Hf isotope data.

Additional information

Funding

Macquarie University Research Development Grant funding to NRD provided financial support to conduct this research.