Oroclines in the Tasmanides (eastern Australia): the twisted nature of orogenic

belts

Chris Fergusson GeoQuEST – SEES –

UoW

Geoscience Australia magnetics (left)

Orogenic belts are regional elongate rock assemblages characterised by compressional structures and commonly related to plate tectonic processes of plate convergence

Oroclines are sharp bends (regional-scale) of/within orogenic belts

NOAA ETOPO1

Rollback in orocline formation. Rosenbaum G., 2014. Geodynamics of oroclinal bending: Insights from the Mediterranean. Journal of Geodynamics 82, 5015.

Rollback of a subduction zone – like a paddle in water https://pixnio.com/sport/canoeing-and-kayaking-pictures/kayak-athlete-man-water-canoe-sport-competition-oar-boat-paddle

Tasmanides – Palaeozoic-Mesozoic orogenic belts (550 to 200 Ma) – eastern third of Australia (modified from Fergusson in press Journal of Geodynamics)

2 examples – Texas and Coffs Harbour oroclines (New England Orogen – south) and Lachlan Orocline (Ross Cayley, Geol Survey of Victoria)

Late Devonian – Carboniferous tectonic elements New England Orogen (modified from Fergusson in press Journal of Geodynamics)

Fergusson (in press). Journal of Geodynamics.

Geoscience Australia magnetics

Geoscience Australia, Geological Survey of Queensland gravity

Pengfei Li et al. (2012). Gondwana Research 22, 279‒289.

Fergusson (in press). Journal of Geodynamics.

Korsch (1981). Journal and Proceedings of the Royal Society of NSW 114, 17‒22.

Seamless geological map of NSW Zone 56 (Gary Colquhoun).

Limestones in hinge of Texas Orocline – but absent from Coffs Harbour Orocline Fergusson (in press). Journal of Geodynamics.

Fergusson (in press). Journal of Geodynamics.

Fergusson (in press). Journal of Geodynamics.

Fergusson (in press). Journal of Geodynamics.

Structural evolution of the early Permian Nambucca Block (New England Orogen, eastern Australia) and implications for oroclinal bending

Shaanan et al. (2014) Tectonics Volume 33, Issue 7, pages 1425-1443, 24 JUL 2014 DOI: 10.1002/2013TC003426 http://onlinelibrary.wiley.com/doi/10.1002/2013TC003426/full#tect20165-fig-0015

http://onlinelibrary.wiley.com/doi/10.1002/tect.v33.7/issuetochttp://onlinelibrary.wiley.com/doi/10.1002/2013TC003426/full#tect20165-fig-0015http://onlinelibrary.wiley.com/doi/10.1002/2013TC003426/full#tect20165-fig-0015http://onlinelibrary.wiley.com/doi/10.1002/2013TC003426/full#tect20165-fig-0015http://onlinelibrary.wiley.com/doi/10.1002/2013TC003426/full#tect20165-fig-0015http://onlinelibrary.wiley.com/doi/10.1002/2013TC003426/full#tect20165-fig-0015http://onlinelibrary.wiley.com/doi/10.1002/2013TC003426/full#tect20165-fig-0015

Fergusson & Colquhoun (2018). Australian Journal of Earth Sciences 65, 303‒333.

Moresi et al. (2014). Nature 508, 245–248.

https://www.youtube.com/watch?v=cVulRP2tUGM

https://www.youtube.com/watch?v=cVulRP2tUGM

Geoscience Australia magnetics SE Australia

Backarc basalts

Backarc basalts Boninites

Boninites

Fergusson & Colquhoun (2018). Australian Journal of Earth Sciences 65, 303‒333.

Spaggiari et al. (2004). Journal of Structural Geology 26, 87‒112.

boninites backarc basin basalts

Spaggiari et al. (2004). Journal of Structural Geology 26, 87‒112.

Packham & Hubble (2016). Australian Journal of Earth Sciences 63, 23–61.

N. Stokes et al. 2015. Australian Journal of Earth Sciences 62, 37–53.

Mirror symmetry across the Melbourne Zone – boninites and backarc basin basalts

Problem – how can the island arc form basement to such a widespread turbidite succession?

NSW South Coast continental slope – boninites, Melville Point backarc basin basalt

Cambrian island arc is not basement to Ordovician turbidites but marginal to it

Izu-Bonin-Marianas island arc ETOPO1 data

Fergusson & Colquhoun (2018). Australian Journal of Earth Sciences 65, 303‒333.

Fergusson & Colquhoun (2018). Australian Journal of Earth Sciences 65, 303‒333.

Fergusson & Colquhoun (2018). Australian Journal of Earth Sciences 65, 303‒333.

Fergusson & Colquhoun (2018). Australian Journal of Earth Sciences 65, 303‒333.

Links to related papers

• Macquarie Arc – turbidites • https://www.tandfonline.com/eprint/KQUXT

H9qnZevnGvP2isR/full • Oroclines in New England Orogen • https://www.sciencedirect.com/science/arti

cle/pii/S0264370717300601

https://www.tandfonline.com/eprint/KQUXTH9qnZevnGvP2isR/fullhttps://www.tandfonline.com/eprint/KQUXTH9qnZevnGvP2isR/fullhttps://www.sciencedirect.com/science/article/pii/S0264370717300601https://www.sciencedirect.com/science/article/pii/S0264370717300601

Conclusions

• Oroclines – curved structural trends based on lithologic/structural data and on magnetics/gravity datasets – New England and Lachlan oroclines

• Oroclines – caused by collision of continental fragments, seamount chains in combination with other factors (ancestral curves, rollback)

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