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Ordovician Macquarie Arc and turbidite fan relationships, Lachlan Orogen, southeastern Australia: stratigraphic and tectonic problems

Journal Article


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Abstract


  • Ordovician rocks of the Lachlan Orogen consist of two major associations, mafic to intermediate volcanic and volcaniclastic rocks (Macquarie Arc), which aerially comprise several north–south-trending belts, and the quartz-rich turbidite succession. Relationships between these associations are integral to resolving their tectonic settings and opinions range between contacts being major thrusts, combinations of various types of faults, and stratigraphic contacts with structural complications. Stratigraphic contacts between these associations are found with volcaniclastic-dominant units overlying quartz-turbidite units along the eastern boundary of the eastern volcanic belt and along the southern boundary of the central volcanic belt. Mixing between these major associations is limited and reflects waning quartzose turbidite deposition along a gently sloping sea floor not penetrating steeper volcaniclastic aprons that were developing around the growing volcanic centres formed during late Middle Ordovician to early Silurian Macquarie Arc igneous activity. An island arc setting has been most widely supported for the Macquarie Arc, but the identification and polarity of the associated subduction zone remain a contentious issue particularly for the Early Ordovician phase of igneous activity. The Macquarie Arc initiated within a Cambrian backarc formed by sea-floor spreading behind a boninitic island arc and presumably reflects a renewed response to regional convergence as subduction ceased along the Ross–Delamerian convergent boundary at the East Gondwana continental margin. An extensional episode accompanied initiation of the late Middle Ordovician expansion in island arc development. A SSE-dipping subduction zone is considered to have formed the Macquarie Arc and underwent anticlockwise rotation about an Euler pole at the western termination of the island arc. This resulted in widespread deformation west of the Macquarie Arc in the Benambran Orogeny and development of subduction along the eastern margin of the orogenic belt.

Publication Date


  • 2018

Citation


  • Fergusson, C. L. & Colquhoun, G. P. (2018). Ordovician Macquarie Arc and turbidite fan relationships, Lachlan Orogen, southeastern Australia: stratigraphic and tectonic problems. Australian Journal of Earth Sciences, 65 (3), 303-333.

Scopus Eid


  • 2-s2.0-85041930349

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=6271&context=smhpapers

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/5217

Number Of Pages


  • 30

Start Page


  • 303

End Page


  • 333

Volume


  • 65

Issue


  • 3

Place Of Publication


  • United Kingdom

Abstract


  • Ordovician rocks of the Lachlan Orogen consist of two major associations, mafic to intermediate volcanic and volcaniclastic rocks (Macquarie Arc), which aerially comprise several north–south-trending belts, and the quartz-rich turbidite succession. Relationships between these associations are integral to resolving their tectonic settings and opinions range between contacts being major thrusts, combinations of various types of faults, and stratigraphic contacts with structural complications. Stratigraphic contacts between these associations are found with volcaniclastic-dominant units overlying quartz-turbidite units along the eastern boundary of the eastern volcanic belt and along the southern boundary of the central volcanic belt. Mixing between these major associations is limited and reflects waning quartzose turbidite deposition along a gently sloping sea floor not penetrating steeper volcaniclastic aprons that were developing around the growing volcanic centres formed during late Middle Ordovician to early Silurian Macquarie Arc igneous activity. An island arc setting has been most widely supported for the Macquarie Arc, but the identification and polarity of the associated subduction zone remain a contentious issue particularly for the Early Ordovician phase of igneous activity. The Macquarie Arc initiated within a Cambrian backarc formed by sea-floor spreading behind a boninitic island arc and presumably reflects a renewed response to regional convergence as subduction ceased along the Ross–Delamerian convergent boundary at the East Gondwana continental margin. An extensional episode accompanied initiation of the late Middle Ordovician expansion in island arc development. A SSE-dipping subduction zone is considered to have formed the Macquarie Arc and underwent anticlockwise rotation about an Euler pole at the western termination of the island arc. This resulted in widespread deformation west of the Macquarie Arc in the Benambran Orogeny and development of subduction along the eastern margin of the orogenic belt.

Publication Date


  • 2018

Citation


  • Fergusson, C. L. & Colquhoun, G. P. (2018). Ordovician Macquarie Arc and turbidite fan relationships, Lachlan Orogen, southeastern Australia: stratigraphic and tectonic problems. Australian Journal of Earth Sciences, 65 (3), 303-333.

Scopus Eid


  • 2-s2.0-85041930349

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=6271&context=smhpapers

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/5217

Number Of Pages


  • 30

Start Page


  • 303

End Page


  • 333

Volume


  • 65

Issue


  • 3

Place Of Publication


  • United Kingdom