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Exploring the Willyama Complex: A Geological Study

Dive into the diverse geology of the Willyama Complex in Central Australia. Discover the ancient rocks, ore bodies, and metamorphic features that shape this unique region. Gain insights into stratigraphy and deformation events through detailed mapping and analysis. Learn about the significance of the Willyama Complex as a source and basement for adjacent rock formations. Unravel the clues left behind by multiple geological processes that have molded this landscape over millions of years.

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Exploring the Willyama Complex: A Geological Study

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  1. The Willyama Complex Setting the scene

  2. 3 main c. 1820 Ma cratons Separated by central Australian orogens

  3. Curnamona Province • Palaeoproterozoic metamorphic basement • Adelaidean sedimentary rocks • Mesozoic &Cenozoic

  4. Willyama Complex • Focus of an enormous amount of work Ag-Pb-Zn orebody • Greenschist to granulite facies inliers -fault contact or unconformably overlain by Adelaidean rocks • Metasediments, orthogneiss, granite and amphibolite bodies • All multiply deformed

  5. Basement rocks • Detailed mapping revealed a stratigraphy within the Willyama Complex metaseds • Can see sedimentary features preserved through effects of metamorphism - give way up features - use marker horizons • Need to establish timing and nature of rock bodies - sedimentary or igneous? • Oldest rocks - 1700 - 1650 Ma • Deformed and metamorphosed at c. 1580 Ma

  6. General progression Upper units - turbidites and other clastic sediments chemical sediments Quartzofeldspathic gneiss with BIF lower units of composite gneiss (migmatite, schist)

  7. Multiple deformation events • See effects of 2 or three regionally penetrative deformation events • Early, bedding parallel foliation deformed by folds with a steeply-dipping axial plane • Retrograde shear zones - D3 • Then effects of another two vents that deformed the Adelaidean series

  8. Metamorphic grade • Greenschist to granulite faciesmeans overall block tilt • Weekeroo - and-st-g-bi-mu q schistshonest amphibolite facies conditions • Peak conditions early • S1, S2 cut by RSZ • And -> sill -> ky

  9. Adelaidean • Series of Neoproterozoic to Cambrian basins throughout Australia • Willyama Complex acted as basement and source - see distinctive cobbles in the Adelaidean rocks • Quartzites±magnetite, dolomites, siltstones are the main lithologies

  10. series • 5 main lithostratigraphic units • Hawker Group - Cambrian limestone and shale • Wilpena Group- shale, silstone,sandstone • Umberatana Group- massive tillites, sandstone and arkoses; laminated silts, shales, carbonates; marine glacials, red sandstone and siltstone • Burra Group - basal sandstone - conglomerate passes into argillite-carbonate sequence • Callana Beds - volcanics, conglomerates, limestone and sandstone unconformable on Mt Painter

  11. Mesozoic and Tertiary • Mesozoic - eastern Australia flooded by shallow seas - GAB and dinosaur fossils • Tertiary - developed laterites, break-aways, opals

  12. And the job to do Information Research Process • Define the task • Locate the information • Selection - what information is relevant to the defining stage • Organizing - how to use the information • Presentation - how to communicate the information to the target audience • Assessing/reflection - how well did I answer the question; what did I learn

  13. 20 minute task • Group 1&2Flow diagram to identify igneous rocksGroup 3 - 10 min review - 2 good points, 2 ways to improve • Group 4 & 5 - sedimentary (Group 6) • Group 7 &8 - metamorphic rocks (Group 9)

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