The structural evolution of the Northern Hastings Block and southern Nambucca Block, southern New England Orogen, eastern Australia

ABSTRACT

The Hastings Block is a weakly cleaved and complexly folded and faulted terrain made up of Devonian, Carboniferous and Permian sedimentary and volcanic rocks. The map pattern of bedding suggests a major boundary exists that divides the Hastings Block into northern and southern parts. Bedding north of this boundary defines an upright box-like Parrabel Anticline that plunges gently northwest. Four cleavage/fold populations are recognised namely: E–W-striking, steeply dipping cleavage S₁ that is axial surface to gently to moderately E- or W-plunging; F₁ folds that were re-oriented during the formation of the Parrabel Anticline with less common N–S-trending, steeply dipping cleavage S₂, axial surface to gently to moderately N-plunging F₂ folds; poorly developed NW–SE-striking, steeply dipping cleavage S₃ axial surface to mesoscopic, mainly NW-plunging F₃ folds; and finally_, a weakly developed NE–SW-striking, steeply dipping S₄ cleavage formed axial surface to mainly NE-plunging F₄. The Parrabel Anticline is considered to have formed during the D₃ deformation. The more intense development of S₂ and S₃ on the western margin of the Northern Hastings Block reflects increasing strain related to major shortening of the sequences adjacent to the Tablelands Complex during the Hunter–Bowen Orogeny. The pattern of multiple deformation we have recorded is inconsistent with previous suggestions that the Hastings Block is part of an S-shaped orocline folded about near vertically plunging axes.

KEYWORDS:

• Northern Hastings Block
• ductile deformation
• folds, cleavages
• structural history
• Nambucca Block
• oroclines

Acknowledgements

The Hastings Block was mapped by BSc (Hons) students from various universities including Bourke (1971), University of New England; Feenan (1984), Hamilton (1980), Kinny (1982), Milligan (1975), Taylor (1984), Thompson (1985) and Deegan (1991), Sydney University; Jeffrey (1986), Rheinberger (1987), Spackman (1989) and West (1990), UNSW; Roberts (2000) from University of Newcastle and Jason (1992) from the University of Technology, Sydney. Evan Leitch is thanked for comments on an earlier draft of this paper, and Bob Henderson, Chris Fergusson, Dick Glen and an anonymous reviewer are acknowledged for improving the final paper. The School of BEES is acknowledged for providing support for field work. Jie Yan acknowledges the support from National Natural Science Funds (U1403292) of China, the Chinese Government for his PhD scholarship and 2013 PESA Tertiary Institution Study Grant.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary Papers

Appendix 1. Domain bedding analysis and macroscopic fold characteristics in NHB.

Appendix 2. Bedding trends in Domains of the NHB–Nambucca Block.

Appendix 3. Characterisation of mesoscopic folds in the NHB–Nambucca Block.

Additional information

Funding

This work was supported by the Chinese Government Scholarship Postgraduate Award [grant number 2011637144]; The University of New South Wales, Faculty Research Grant Progam [grant number PS27189] and National Natural Science Funds [grant number U1403292].