1Umer Habib, 1Sebastien Meffre, 2Ralph Bottrill
1Centre of Ore-Deposit Geology and Earth Sciences, University of Tasmania, Australia; 2Mineral Resources Tasmania, Rosny Park, Hobart, Australia
The preservation of dismembered ophiolites in major fault zones of the central Lachlan Orogen suggests complex oceanic crust formation along the East Gondwana margin during the Early to Late Cambrian. The ophiolite sequences exposed at Heathcote, Dookie and along the Governor Fault zone in Victoria, are multiply deformed and preserve spectacular examples of fault propagation duplex systems with accretion of oceanic crust. Understanding when they were formed and emplaced is crucial for understanding the evolution of the Lachlan Orogen to constrain when sea floor spreading and terrane accretion occurred. In this study LA-ICPMS (U/Pb) zircon ages are used to get detailed age information for the Lachlan ophiolite sequences. Ophiolitic layered, structurally complex gabbro from Tatong gave an age of 518±4.1 Ma. Gabbro samples from Dookie yielded ages of 513±4.4 and 515±4.0 Ma. These are similar to the 516±0.9 Ma age calculated for the McIvor Hill gabbro from the Mt Read Volcanic belt in Tasmania from a previous study. Detrital zircons in cherts from the Dookie complex are 8 million years younger at 508±4.6Ma. Detrital zircons from the Knowsley East shales from the northern part of the Heathcote Cambrian volcanic rocks were 18 million years younger at 490±4.3 Ma. These new data, combined with previously published zircon ages, suggest a 2-stage evolution (~518-505 Ma and 502-490Ma) for Central Victorian ophiolites.
Keywords: Palaeozoic, Ophiolites, Lachlan Orogen, Geochronology
Umer did his honors and masters in geology from Pakistan and worked for MOL from 2012-2015.