Paleomagnetism of the Carboniferous Rouchel Block, Tamworth Belt, and pole path revision for the New England Orogen, eastern Australia

ABSTRACT

Structural, magnetic and gravity trends of the southern New England Orogen (SNEO) indicate four oroclinal structures, none conclusively confirmed paleomagnetically. Curved structures of the Tamworth Belt (TB)—a continental forearc exposed across six tectono-stratigraphic blocks with interlinked Carboniferous stratigraphies and extensive ignimbritic rocks known to retain primary magnetisations despite prevalent overprinting—are prospective to oroclinal testing through comparison of Carboniferous pole paths for individual blocks. Pole paths (a) have been established for the Rocky Creek and Werrie blocks (northwestern/western TB), (b) are described herein for the Rouchel Block (southwestern TB), and (c) are forthcoming for the Gresford and Myall blocks (southern/southeastern TB). The Rouchel path derives from detailed paleomagnetic, rock magnetic and magnetic fabric studies. Thermal, alternating field and liquid nitrogen demagnetisations show a low-temperature overprint, attributed to late Oligocene weathering, and high-temperature (HT) primary and overprint components in both magnetite and hematite carriers, showing slight, systematic, directional differences with hematite providing the better cleaned site poles. Seven primary mean-site poles of Tournaisian and mainly Visean age and three overprint poles show six positive fold tests, five at 95% or higher confidence levels. Two dispersed groupings of intermediate (IT) and HT overprint site poles of Permian and Permo-Triassic age are attributed to early and late phases in oroclinal evolution of the SNEO. HT and IT/HT overprint site poles of mid-Carboniferous age are attributed to Variscan Australia–Asia convergence. Individual pole paths for the Rocky Creek, Werrie and Rouchel blocks show no noticeable rotation between them, indicating primary curvature for the southwestern TB. Their integrated SNEO pole path establishes a reference frame for determining rotations of the southern and southeastern TB.

KEYWORDS:

• Carboniferous
• magnetic fabric
• New England Orogen
• orocline
• paleomagnetism
• pole path
• rock magnetism
• Rouchel Block
• Tamworth Belt

Acknowledgements

Many thanks to John Roberts (UNSW) for generous provision of geological compilation maps providing crucial fieldwork guidance, to Rob Barnes (GSNSW) for digital geological maps, to Andrew Cross (GA) for GIS assistance, to Peter Flood (UNE) for regional guidance, to Peter Percival (GA) and Hervé Theveniaut (GA/BRGM) for field assistance, to Uros Rokvic (GA), Peter Percival, David Edwards (ANU), Hervé Theveniaut and Xiang Zhao (ANU) for laboratory assistance, to John Giddings (GA) for processing assistance, to Alexandra Abrajevitch (ANU) for rock magnetic insights, to Phil McFadden (GA) for his fold test program, to Cor Langereis (Utrecht University) for the ANIPO magnetic fabric program, to David Heslop (ANU) for his FORC processing program, to Brad Pillans, Andrew Roberts and David Heslop for access to the Black Mountain Paleomagnetic Laboratory (RSES/ANU), to David Ellis, Richard Arculus, Patrick De Deckker, Bear McPhail, Brian Kennett, Andrew Roberts, Ian Jackson and Steve Eggins for visiting fellowships at ANU, and to Uri Shaanan, Augusto Rapalini and an anonymous reviewer for in-depth reviewing and sound advice on presentation. Funding by the Australian National University Faculties Research Grants Scheme, Grant F02020 (CK), is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author.

Supplementary Papers

Figure S1 Day et al. (1977) plots for the Rocky Creek (a) and Werrie (b) blocks based on hysteresis parameters Mr, Ms and Bc and backfield parameter Bcr. One representative specimen per site (Klootwijk, 2002, table 1, 2003, table 1). See Figure 9 for comparable Day plot for the Rouchel Block.

Table S1 Reversal test (McFadden & McElhinny, 1990) for primary and overprint components (P, P2, R), Martins Creek Ignimbrite Member.

Table S2 Pseudo-primary (P1) and primary (P), high-temperature (HT), components in stratigraphic coordinates, Rouchel Block. See Supplementary Tables S3, S5.

Table S3 Fold test (McFadden, 1990), mean-site directions, pseudo-primary components (P1, P).

Table S4 Reversal test (McFadden & McElhinny, 1990) for pseudo-primary (P1) and primary and overprint (P, R) components, Martins Creek Ignimbrite Member.

Table S5 Mean-site poles, pseudo-primary and primary components (P1, P).

Table S6 Low-temperature overprint components (L, L0, L1, L2, L3) in geographic coordinates, see Figure 14.

Table S7 High (P, R) and intermediate to high (N, S, O, Q, W) temperature overprints.

Table S8 High (P, P3, R) and intermediate to high-temperature (Q, N, S, O, W) components of unclear origin.

Table S9 Susceptibility anisotropy for analysed sites in stratigraphic coordinates.

Table S10 Composite pole path for Rocky Creek, Werrie and Rouchel blocks of the western Tamworth Belt (SNEO pole path, Figures 13c, 16).

Additional information

Funding

Australian National University, Faculties Research Grants Scheme ID: F02020 to CT Klootwijk