FT3 – Out with the old, in with the new — a traverse across the Archean-Proterozoic boundary in the Mount Bruce Supergroup (July 29-Aug 4)
(Guides: David Martin, Heather Howard) The Archean-Proterozoic boundary has always been regarded as reflecting a fundamental change in Earth surface processes and environments. However, the practicality of the currently accepted chronometric definition is increasingly being questioned. This trip will explore these processes and their products as documented in the exceptional Neoarchean to earliest Paleoproterozoic exposures of the Fortescue, Hamersley and Turee Creek Groups in Western Australia, and evaluate candidates for a chronostratigraphic GSSP related to the Great Oxidation Event.
FT4 – A traverse across the Yilgarn Craton in Western Australia – from the Jack Hills to the Youanmi Terrane (July 29-Aug 4)
(Guides: Tony Kemp, Ivan Zibra) The one-week excursion will feature an west to east traverse across the northern Yilgarn Craton, combining geophysical, structural, geochemical, geochronological and isotopic data to outline the tectono-magmatic and metamorphic evolution of this large remnant of Eo- to Neoarchean continental crust. The excursion will start in the western corner of the craton, in the Narryer Terrane. Rocks of the Mt Narryer and Jack Hills metasedimentary belts, which both contain Hadean (> 4000 Ma) detrital zircon crystals, will be examined, along with flanking ancient quartzofeldspathic gneisses that have protolith ages from 3730 Ma to 2750 Ma. Granitic outcrops associated with cratonisation from 2680-2620 Ma will also be visited. In the western part of the Youanmi Terrane, the excursion will mainly focus on the structures developed during the c. 2730–2660 Ma Yilgarn Orogeny, with the aim of discussing the relationship between shearing, magmatism and crustal evolution from the thin-section scale up to the crustal scale. Main highlights include the Moyagee Fault near Mount Magnet, which represents the oldest-known seismogenic fault on Earth. The final part of the excursion will offer an overview on the c. 2750 Ma Yalgoo Dome, offering a glimpse of the tectonic style that prevailed during preorogenic times, which was characterized by large-scale granitic diapirism.
FT5 – Mineral Deposits in the Yilgarn Craton (July 29th to August 4th or 5th)
(Guides: Steffen Hagemann, Nico Thébaud) The Yilgarn Craton has long been recognised as having world class Au endowment. Yet the endowment varies dramatically between terranes of the Yilgarn and between constituent geological domains, showing a tendency to cluster in districts or ‘camps’. The one week excursion will visit classic geological localities and gold deposits from the Yilgarn Craton showcasing the deposit style diversity and focusing on Au mineral system formation from regional down to deposit scale formation.