https://ogma.newcastle.edu.au/vital/access/ /manager/Index en-au 5 Volcanic evolution of a long-lived Ordovician island-arc province in the Parkes region of the Lachlan Fold Belt, southeastern Australia https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:3347 Sat 24 Mar 2018 07:18:34 AEDT ]]> Volcanology, geochemistry and structure of the Ordovician Cargo Volcanics in the Cargo-Walli region, central New South Wales https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:3346 25) Zr/Nb values. However, the Walli Volcanics are readily differentiated from the Cargo Volcanics by their higher P₂O₅ contents and likely high-K calc-alkaline to shoshonitic affinities. The Cargo Volcanics are intruded by Cu - Au mineralised, plagioclase + hornblende + quartz-phyric dacites with medium-K calc-alkaline affinities. These dacites have lower TiO₂ and higher MgO contents at any SiO₂ level compared to the Cargo Volcanics, and are compositionally similar to Late Ordovician to Early Silurian (453 - 441 Ma) dacites at Copper Hill and in the Narromine Complex. However, at Cargo, clasts derived from the dacites are locally abundant in volcaniclastic conglomerate near the top of the Cargo Volcanics, indicating that the dacites were intruded and exhumed prior to deposition of the Barrajin Group limestones, which commenced at ca 454 Ma in this area. The dacites at Cargo are intruded by small, apparently unmineralised monzonitic intrusions with shoshonitic affinities, which also appear to pre-date deposition of the Barrajin Group. LA-ICPMS U - Pb dating of detrital zircons from the Ranch Member at the base of the Daylesford Limestone (basal Barrajin Group) revealed a dominant population with an average age of 453.0 ± 4.1 Ma (identical within error to the mid-Ea1 age for the host sediments based on fossil assemblages) and subordinate populations with average ages of 480 Ma and 505 Ma. The 453 Ma zircons were most probably derived from either the intrusive dacites or monzonites, suggesting that the Cargo region was rapidly exhumed following emplacement of the felsic intrusions. The angular unconformities near and at the top of the Cargo Volcanics and the broadly coincident change in magma chemistry suggest that this sector of the Macquarie Arc underwent major tectonic upheaval commencing in the latest Gisbornian - early Eastonian. The Cargo Volcanics are interpreted to have undergone major eastward translation at this time (from an original position now buried beneath the Cowra Trough). Their present juxtaposition with the contiguous Molong Volcanic Belt probably did not occur until the late Early Silurian during the final stages of the Benambran Orogeny.]]> Sat 24 Mar 2018 07:18:34 AEDT ]]>