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.

TawnyCALC is coming

The tawny frogmouth. Possibly Australia’s
most delightful bird? Although competition
is fierce. (Photo by James Barron.)

Looking ahead, Eleanor and John have just been discussing TawnyCALC, one of two upcoming extension packs to THERMOCALC.

TawnyCALC will automate various problems that involve driving THERMOCALC along a path, doing dogmin calculations at each step. Fractionation calculations are an obvious example. We currently plan to have it running online via a Jupyter interface.

The second extension pack, TammaCALC, will allow a set of phase diagram calculations to be made simultaneously and repeatedly. It will facilitate various uncertainty calculations.

More to come in 2020!

cpxwing log entry 001

Mushrooms and clinopyroxene –
a good combination?

This is Simon’s blog reporting on the development of a new single-clinopyroxene HPx-EOS.

The new model is designed to replace pre-existing versions that do not currently overlap in P—T—x space.

So far three clinopyroxene EOS exist. Ordered diopside—omphacite—jadeite (Green et al., 2007) is for coexisting sodic—calcic clinopyroxenes. It accounts for order—disorder on the octahedral M1 and M2 sites, but not on the tetrahedral T sites. It is appropriate for high pressure but unsuitable for high temperatures.

Continue reading “cpxwing log entry 001”