Team news – October 2020

A quick round-up of news on team members and projects related to the HPx-eos and THERMOCALC:

Simon Schorn recently moved to Austria, where he has been awarded a grant to work at the University of Graz on fluid infiltration during metamorphism. Congratulations Simon! He had a strange year as Eleanor’s post-doc in Melbourne, spending two thirds of it in actual or effective lockdown, but we look forward to continued collaboration and a belated farewell dinner once international travel resumes. While in Melbourne, Simon did excellent work on cpx- and amphibole-bearing equilibria in subsolidus metabasite systems, making key insights that will help us with modelling the blueschist facies. His monstrous new cpx x-eos, cpx-wing, just needs its laser cannons added before it’s ready for take-off.

Springtime in Melbourne. I need to work on my eucalypt identification.

Corinne Frigo has just completed a marathon experimental programme at ANU, which has highlighted where we could improve the igneous x-eos in dry peridotite systems. We appreciate Corinne’s results all the more because she has persevered with her work through bushfires, a devastating hailstorm that put her lab out of action, and the pandemic. Well done Corinne!

John Mansour has done some magnificent work on TawnyCALC – and the delay in completing and releasing it is entirely my fault, sorry John! More news on this soon.

Katy Evans rightly pointed out that the set of hydrated ultramafic x-eos used in Evans & Powell (2015; J Metam Geol 33 649-670) should be on this site. She has been preparing the input files for this, and they should be ready to go shortly.

RP is focusing on updates to THERMOCALC 3.50. He has implemented a number of changes to the scripting, aimed at making it simpler, more transparent, and better at helping the user when things go wrong. He is currently restoring some functionality related to calculations with fluids that has been lost in recent versions. Once a new version of the program is ready for release, we will also be able to make Simon’s long-awaited pseudosection tutorial available, with up-to-date scripts.

Tim Holland continues to develop the datas et and igneous-set x-eos. In particular: an update for peridotite melting relations; updates for Ti in various phases (ru, ilm, melt); updating spinels with Eleanor; adding CO2 and S to melts, the last two in quite early but promising stages; working with RP on a simple ternary feldspar model that is continuous in composition (without the distinct C1/I1 phases); and on a nepheline model with Owen Weller.

Finally, in between battles with high-Ca opx and cpx-wing, Eleanor Green has been investigating some xenolith data from the Lesser Antilles volcanic arc, collected by Jon Blundy’s team at the University of Bristol. The xenoliths sample the upper part of the magmatic system that created each island, and their whole-rock chemistry and mineral assemblages contain insights into how this magmatic system varies along of the arc. These rocks are very high variance – they have many dimensions of significant compositional variability, but few phases – so forward modelling has proved too challenging for the current generation of x-eos. Fortunately, this is where the (S)COlP barometers come in useful.

Profiles of the team can be found here. We welcome questions and comments, via the comment form, or, even better, the Discussion Group.

Testing the x-eos in small peridotitic systems

Corinne Frigo has been visiting Melbourne from ANU. Corinne is working with Hugh O’Neill, Richard Arculus and Eleanor on ARC Discovery Project DP170100982, A new perspective on melting in the Earth and the origin of basalts. She has some very interesting experimental results on peridotite melting in CMAS + Cr2O3 + K2O at 30 kbar, which contrast nicely with the experiments of Liu & O’Neill (2004) at 11 kbar.

At Tiamo in Lygon Street for breakfast – photo by Simon.

The experiments are giving the x-eos a workout! Currently, the model pyroxenes are taking too much Al2O3 in high-Cr2O3 bulk compositions, meaning that we should revise the Al-Cr partitioning here. Experiments in small systems are extremely useful, providing constraints that can’t be extracted from the natural system data available. Eleanor and Corinne will continue to look at this problem over the next few months, and their new insights will ultimately be incorporated into the next generation of igneous x-eos.

Modelling experiments at ANU

Eleanor has been at the Australian National University in Canberra visiting Corinne Frigo. Corinne has recently begun a complex program of experiments on the generation of basalt-analogue melts in the CMAS±Cr system. The new igneous set of HPx-eos do not agree too well with Corinne’s initial experiments. This is not really a surprise at this stage, but we have some work to do before we can understand what is wrong.

Corinne is working with Hugh O’Neill, Richard Arculus and Eleanor on ARC Discovery Project DP170100982, A new perspective on melting in the Earth and the origin of basalts. In this project we have the opportunity for close interaction between the experimental program and the internally-consistent modelling work. Enlightening and fun! Corinne will present some of this work at Goldschmidt on 21st August.

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When	What	Where
5-9 September 2022	Understanding oxygen fugacity in geoscience: international school	Trieste, Italy

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