Habib, Umer1, Leslie, Chris1, Meffre, A/Prof. Sebastien1, Schaap, Thomas1, Wells, Tristan1
1CODES, University of Tasmania, Hobart, Australia
The Lachlan Orogen has a long and complicated geological history involving:
- Cambrian collision and orogenesis
- Ordovician continental-derived sediment deposition
- Ordovician island arc development formation of porphyry and epithermal deposits
- Silurian orogenesis and extension and formation of volcanic-hosted massive sulphide deposits
- Devonian orogenesis and formation of granite-related deposits
This geological framework is well-supported by data from many previous studies. However, the exact plate configurations responsible for these geological events remain poorly constrained. These constraints are required to make predictions about the location of ore deposits and to gain a better understanding of the structure and composition of the continental crust.
New data acquired throughout the Lachlan orogen over recent years combined with data from previous studies have helped to improve scientific knowledge showing that:
- During the earliest geological history of the Lachlan Orogen there was at least 2 Cambrian arcs: one continental and the other oceanic. The continental arc extended along the western edge of the orogen. The intra-oceanic island was dismembered after it collided with the Selwyn Block and Tasmania.
- Geochemical and geochronology data from the Melbourne zone and the Selwyn block in Victoria show that most of this zone is likely underlain by crust containing juvenile components rather than thick Mesoproterozoic continental crust.
- The intra-oceanic Macquarie Arc began approximately 10 Ma after the end of the Cambrian magmatism and was active for a further 40 million years.
- Magmatism in Macquarie Arc began to be contaminated by continental material starting at 450 Ma in the Molong area. Continental contamination and porphyry development occurred at different times within the magmatic history of the arc.
- The Lachlan Orocline model explains much of the tectonic evolution of the area from the latest Ordovician through to Devonian periods.
Although these constraints are useful in refining the tectonic models, many details remain unresolved and uncertain.
Sebastien Meffre is Associate Professor at the University of Tasmania. He is the head of Earth Sciences and also works within the Centre for Ore Deposit and Earth Sciences (CODES). His current research interests include: the U-Pb isotopic system, understanding the plate tectonic processes and interactions and geochemistry.