Paper No. 5
Presentation Time: 9:00 AM-6:00 PM
THE 1.60-1.57 GA EVENT OF AUSTRALIA
FORBES, Caroline J., Centre for Mineral Exploration Undercover (CMXUC), University of Adelaide, Mawson Building, North Terrace, Adelaide, 5005, Australia, GILES, David, Centre for Mineral Exploration Undercover (CMXUC), University of Adelaide, Adelaide, 5005, Australia and VAN DER WIELEN, Simon, Deep Exploration Technologies CRC (DET CRC), Adelaide, 5005, Australia, caroline.forbes@adelaide.edu.au
Australia shows a complex geological record between ca. 1.60-1.57 Ga involving high-temperature/low-pressure (HTLP) metamorphism, deformation, magmatism and mineralisation. This record is important in terms of understanding plate reconstructions, mineralising systems (e.g. Olympic Dam Cu-Au-U-REE and Prominent Hill IOCG deposits), and in knowledge of ancient versus modern geological processes. Evidence of the ca. 1.60-1.57 Ga event is preserved over an area greater than 3 million square kilometres across the Australian continent, yet is scarce elsewhere on the planet. The driving mechanism for deformation and extensive high-temperature/low-pressure metamorphism and hence the tectonic context of this event are equivocal, as is an explanation for its geographic extent and apparent synchronicity. Magmatism associated with this event includes one of the world’s most voluminous single outpourings of felsic lava, and was co-magmatic with extensive intrusives. The magmas are spatially and temporally associated with the formation of giant ore deposits (e.g. Olympic Dam).
The complexity and geographic extent of the ca. 1.60-1.57 Ga event creates confusion in attempting to understand the mechanisms of the event, and major questions remain unanswered, including: What do we really know about the deformation and metamorphic conditions of active regions at this time? What was the role of radiogenic heat in potential thermal weakening to focus deformation and as a mechanism for elevated geothermal gradients? What was the mechanism of extensive HTLP metamorphism and does this relate to voluminous magmatism? How, what and why is there an association with major mineral systems?
It is possible, and likely, that the ca. 1.60-1.57 Ga event developed by a combination of overprinting mechanisms. Understanding the event requires separating the key geological components and assessing how they could individually develop before addressing how they might overprint one another. Here, we look separately at the mechanisms of the HTLP tectonothermal event and the generation of voluminous felsic magmas in order to develop an overall picture of the tectonic architecture of the Australian continent at this time.
