I’ve just issued an update to the igneous set of x-eos, involving tiny changes to the thermo of orthopyroxene (provided by Tim Holland). This should prevent high-Ca orthopyroxene from being stable, as has been seen in some calculations on peridotite. I’ll let Jamie Connolly know, so hopefully this change will shortly be implemented in Perple_X too.
Update Oct 2020: This did not solve the problem…. A further, hopefully successful update will follow shortly.
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.
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.
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.