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GSA GOLD (GSA Geoscience Online Lecture & Discussion)

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GSA GOLD is an online lecture and discussion series from the Geological Society of Australia, held on the first Tuesday of the month.

About this Event

The November GSA GOLD is on 3 Nov 2020 {1.00pm AEDT (NSW, ACT, VIC, TAS), 12.00pm AEST (QLD), 12.30pm ACDT (SA), 11.30am ACST (NT), 10.00am WST (WA)}!

Our November speaker is Dr Anthony Reid.

Talk title: Magmas, metasomatism and the mantle: a journey through three papers I wish I had read earlier in my career

Dr Anthony Reid works as Senior Principal Geoscientist with the Geological Survey of South Australia. With a background in geochronology and structural geology, Anthony has worked on the Gawler Craton and related geology of South Australia for the past 16 years. His PhD was on the geology of eastern Tibet.

Registration for GSA GOLD is free for all GSA members. Non-members can also register for just $10.00.

Non-members can use the GSA GOLD registration fee as part of their joining fee when applying for membership with the Geological Society of Australia. Please email info@gsa.org.au for info.

Following your registration, you will be sent a link to attend GSA GOLD on Zoom.

Talk Abstract:

In this talk I’m going to discuss three key papers that I would give to my younger self to read.

Admittedly, choosing three papers from many was difficult, but these are papers that I learnt so much from. Two of these papers I’ve read, one I’ve written.

Firstly, what is the significance of the dark blobs you sometimes see in granites? Previously I had no idea, really. That was until I worked with my Geological Survey of South Australia colleague Mark Pawley on the magmatic rocks exposed in spectacular coastal outcrops of the western Gawler Craton. Out of that we wrote a paper this year (2020) on a 1.62 Ga igneous suite that is (from my side at least) an attempt to make sense of magma mingling, mixing and magma transfer.

Secondly, what happens when fluids are the dominant force driving mineral crystallisation, rather than pressure or temperature? The mineralogy of metasomatic rocks can be weird. Messy even. I had worked in the eastern Gawler Craton iron oxide-copper-gold terrane for several years, but it took a trip to Quebec before I could piece together what the mineral assemblages were telling me. That was thanks to work by Louise Corriveau in the Great Bear terrane, as described in her 2016 paper.

Finally, the mantle. Deep, mysterious, green. Electrical geophysics and isotope geochemistry shows that is actually quite complicated down there. But is it really that important? Yes! Double yes! And a 2009 paper by Graham Begg on the evolution of Africa really brought this home. What is a craton, and how important is mantle structure is in controlling magmatic and metallogenic processes?

All of these papers have been instrumental in building the mental map I use to navigating geology. So this talk will be a journey from the bottom of the lithosphere towards the mineral deposit. If you are free, you might like to join me for the ride.

References:

Begg, G.C., Griffin, W.L., Natapov, L.M., O'Reilly, S.Y., Grand, S.P., O'Neill, C.J., Hronsky, J.M.A., Djomani, Y.P., Swain, C.J., Deen, T., Bowden, P., 2009. The lithospheric architecture of Africa: Seismic tomography, mantle petrology, and tectonic evolution. Geosphere 5, 23-50.

Corriveau, L., Montreuil, J.-F., Potter, E.G., 2016. Alteration Facies Linkages Among Iron Oxide Copper-Gold, Iron Oxide-Apatite, and Affiliated Deposits in the Great Bear Magmatic Zone, Northwest Territories, Canada. Economic Geology 111, 2045-2072.

Reid, A.J., Pawley, M.J., Wade, C., Jagodzinski, E.A., Dutch, R.A., Armstrong, R., 2020. Resolving tectonic settings of ancient magmatic suites using structural, geochemical and isotopic constraints: the example of the St Peter Suite, southern Australia. Australian Journal of Earth Sciences 67, 31-58.

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