Tectonic cycles in the Strangways Metamorphic Complex, Arunta Inlier, central Australia: geochronological evidence for exhumation and basin formation between two high-grade metamorphic events*

Abstract

Deformation, metamorphism and magmatism during the Strangways Orogeny in the eastern Arunta Inlier of central Australia appears to be a result of plate-margin-related tectonism along the southern margin of the North Australian Craton. SHRIMP zircon dating of basement and cover sequences in the Strangways Metamorphic Complex indicates that the Strangways Orogeny consisted of two distinct tectonothermal cycles between ca 1.79 and ca 1.71 Ga. Sedimentary protoliths of the Mt Bleechmore Granulite were deposited after ca 1.8 Ga and probably metamorphosed at ca 1.78 Ga (the Early Strangways Event). These rocks were subsequently exhumed and eroded, forming a basement on which the Ledan Package (Mendip Metamorphics, Ledan Schist and Utopia Quartzite) was deposited after ca 1.77 Ga. Metamorphic zircon overgrowths (1723 ± 9 Ma) and a pegmatite intrusion (1730 ± 4 Ma) in the Mendip Metamorphics record a second phase of deformation and metamorphism (the Late Strangways Event). The arc-like Huckitta and Inkamulla Granodiorites in the eastern Strangways Metamorphic Complex were intruded at 1762 ± 3 Ma and 1773 ± 4 Ma, respectively, suggesting that the Early Strangways Event was associated with subduction along the southern margin of the North Australian Craton. Exhumation and basin formation between the two periods of contraction was possibly a consequence of extension after the Early Strangways Event and related to A-type magmatism at ca 1.74 Ga in the eastern Strangways Metamorphic Complex. Metamorphic zircon overgrowths in the Huckitta Granodiorite have an age of 332 ± 3 Ma and record a phase of relatively high-grade metamorphism towards the end of the Alice Springs Orogeny.

Keywords:

• Arunta Inlier
• geochronology
• granulite
• Huckitta Granodiorite
• Inkamulla Granodiorite
• Ledan Schist
• Mendip Metamorphics
• metamorphism
• SHRIMP
• Strangways Metamorphic Complex
• uranium – lead dating
• zircon

ACKNOWLEDGEMENTS

Bill Collins, Ian Scrimgeour, David Huston and George Gibson are thanked for constructive reviews of the manuscript. Jon Claoué-Long is thanked for sharing his ideas and data on the eastern Arunta. The assistance of Stuart Whittet in the field is greatly appreciated. DWM publishes with permission of the Chief Executive Officer, Geoscience Australia.

Notes

*Tables 1 – 6 indicated by an asterisk (*) in the text are Supplementary Papers; copies may be obtained from the Geological Society of Australia's website (www.gsa.org.au) or from the National Library of Australia's Pandora archive (http://nla.gov.au/nla.arc-25194).

Additional information

Notes on contributors

DW Maidment

*Tables 1 – 6 indicated by an asterisk (*) in the text are Supplementary Papers; copies may be obtained from the Geological Society of Australia's website (www.gsa.org.au) or from the National Library of Australia's Pandora archive (http://nla.gov.au/nla.arc-25194).