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The Willyama Complex

The Willyama Complex. Setting the scene. 3 main c. 1820 Ma cratons Separated by central Australian orogens. Curnamona Province. Palaeoproterozoic metamorphic basement Adelaidean sedimentary rocks Mesozoic & Cenozoic. Willyama Complex.

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The Willyama Complex

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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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