The Keepit arc: provenance of sedimentary rocks in the central Tablelands Complex, southern New England Orogen, Australia, as recorded by detrital zircon

ABSTRACT

Detrital zircon from the Carboniferous Girrakool Beds in the central Tablelands Complex of the southern New England Orogen, Australia, is dominated by ca 350–320 Ma grains with a peak at ca 330 Ma; there are very few Proterozoic or Archean grains. A maximum deposition age for the Girrakool Beds of ca 309 Ma is identified. These data overlap the age of the Carboniferous Keepit arc, a continental volcanic arc along the western margin of the Tamworth Belt. Zircon trace-element and isotopic compositions support petrographic evidence of a volcanic arc provenance for sedimentary and metasedimentary rocks of the central Tablelands Complex. Zircon Hf isotope data for ca 350–320 Ma detrital grains become less radiogenic over the 30 million-year record. This pattern is observed with maturation of continental volcanic arcs but is opposite to the longer-term pattern documented in extensional accretionary orogens, such as the New England Orogen. Volcanic activity in the Keepit arc is inferred to decrease rapidly at ca 320 Ma, based on a major change in the detrital zircon age distribution. Although subduction continues, this decrease is inferred to coincide with the onset of trench retreat, slab rollback and the eastward migration of the magmatic arc that led to the Late Carboniferous to early Permian period of extension, S-type granite production and intrusion into the forearc basin, high-temperature–low-pressure metamorphism, and development of rift basins such as the Sydney–Gunnedah–Bowen system.

KEYWORDS:

• detrital zircon U–Pb–Hf–trace elements
• Wongwibinda Metamorphic Complex
• accretionary wedge
• New England Orogen
• Carboniferous Keepit arc evolution
• provenance
• turbidites

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. E. A. Belousova is thanked for help in the field and laboratory with the TerraneChron sampling and processing. P. A. Cawood, T. Raimondo and G. Rosenbaum are thanked for comments made on a thesis chapter version of this research. Critical reviews by Pengfei Li and Robin Offler 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 913 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1142 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au/).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary Papers

Table 1 U–Pb isotopic data for all zircon analyses.

Table 2 Trace-element data for all zircon analyses.

Table 3 Hf isotopic data for all zircon analyses.

Additional information

Funding

Macquarie University [grant number NA].