Timing and development of oroclines in the southern New England Orogen, New South Wales

Abstract

⁴⁰Ar/³⁹Ar dating of slate and phyllite in the Nambucca Block, southern New England Orogen, indicates that deformation took place between 264 and 260 Ma. These data further show that indentation of the Early Permian turbidite successions by the southward-moving Coffs Harbour Orocline ceased at this time. Folding of the Sakmarian to Sarginian sequences in the Silver Spur Basin (294.6 – 275.6 Ma) during the megafolding event constrains the formation of the Texas Orocline to be post-ca 276 Ma. The presence of brachiopod faunas indicates that orocline formation commenced in the early Kungurian (ca 273 Ma) during the early stages of the Hunter – Bowen Orogeny. Thus, development of the Texas and Coffs Harbour Oroclines took place within a period of 13 million years, from 273 to 260 Ma. Oblique convergence is believed to be responsible for the formation of the Texas and Coffs Harbour Oroclines and associated constrictional structures during the Hunter – Bowen Orogeny. Slip on a dextral, strike-slip fault formed during convergence, buckled and rotated the meridional-trending arc – forearc – subduction complex to form north-northwest-trending, Z-shaped megafolds.

KEY WORDS:

• ⁴⁰argon –³⁹argon dating
• Coffs Harbour Orocline
• Manning Orocline
• New England Orogen
• New South Wales
• oroclines
• Texas Orocline

Acknowledgements

We are grateful to Russell Korsch for reading and commenting on the first draft of this paper and to Dick Glen and Peter Cawood for making constructive comments that greatly improved the manuscript. We also thank Bill Landenberger for discussions about the Hillgrove Suite. Jiang Zhiyu and Olivier Rey-Lescure are also thanked for drafting the figures.