Script round-up: calcsdnle

In THERMOCALC, versions up to and including the December 2020 release of TC 3.50, it is possible to print partial uncertainties (standard deviations) on calculated compositional variables and modes of phases. This is done using the script

calcsdnle yes

where the name of the script can be read as “calculate standard deviations on non-linear equations”.

When using this facility, it’s important to be aware that:

(1) The uncertainties that are printed are only those that stem from the dataset uncertainties. They do not include the uncertainties associated with the activity−composition relations, or with end-members that are not taken from the dataset. The uncertainties that are not captured by the calcsdnle script are generally larger, or much larger, than the dataset uncertainties.

(2) The uncertainties associated with the different compositional variables and modes are correlated, although the correlations are not given in the output. The correlations may mean that, with a small change in the thermodynamic input, two isopleths might intersect in a very different region of P-T space, come to intersect in a plausible P-T window when they did not previously, or cease to intersect in a plausible P-T window when they did previously (this is a starting point for understanding the upcoming avPT+ approach to uncertainty analysis).

A new x-eos for ternary feldspars

What’s new?

We have published new x-eos for plagioclase and alkali feldspars:

TJB Holland, ECR Green & R Powell (2021). A thermodynamic model for feldspars in KAlSi3O8-NaAlSi3O8-CaAl2Si2O8 for mineral equilibrium calculations. Journal of Metamorphic Geology, 1-14. DOI: 10.1111/jmg.12639

The preferred ternary feldspar x-eos in this paper is the 4TR model (the name is discussed below). This single x-eos replaces two previous x-eos: the Ibar1 and Cbar1 ternary feldspar x-eos of Holland & Powell (2003), Contributions to Mineralogy and Petrology, 145 492-501.

Additionally, we have introduced a binary x-eos to represent low albite with minor dissolved Ca. This can be used to model the peristerite gap in metabasites, where previously we used pure end-member albite.

Continue reading “A new x-eos for ternary feldspars”

fO2 workshop/school this September

Please consider pre-registering for the following event!:

Understanding oxygen fugacity in Geoscience is a workshop/school running 5-9 September 2022, to highlight the state of the art, major debates and some case studies about redox processes and oxygen fugacity from the Earth’s interior to the surface. It will bring together experts from various disciplines and it is directed to students and scientists with background on chemistry and physics of the Earth and planetary interiors. The School is hosted by the Department of Mathematics and Geosciences, University of Trieste. We also hope to make the School available to online-only participants.

Eleanor Green and Katy Evans are among the speakers and practical leaders at this School, which will address thermodynamic modelling in addition to experimental, analytical and observational themes.

We thank Luca Ziberna for proposing this School, for patiently persisting with the idea throughout the disruption of the pandemic, and for his exceedingly hard work in leading the Organizing Committee!

Modelling deserpentinization

Serpentinite from the Thetford Mines Ophiolite Complex, Ordovician; Thetford Mines area, Quebec, Canada. Attribution: James St. John,, via Wikimedia Commons

In a recent paper, Katy Evans and Ronald Frost discussed deserpentinization as a source of oxidation in arc magmas.

You can access their THERMOCALC thermo datafiles here. The a-x relations were developed by Roger Powell, for Rebay, Powell & Holland, in prep.

A new THERMOCALC 3.50 for the solstice

Latest update 21 December 2020

We have updated THERMOCALC 3.50!

The scripts have changed a lot. A guide to the new scripts is bundled with the software download, and we have also updated all existing documentation and tutorials to reflect the changes. (Looking back, I see I previously claimed that scripts in tc350 were unlikely to change further – this proved to be as wrong as any other prediction about 2020.)

Progress represented in this update includes:

  • Scripts are now more concise and more self-explanatory, and THERMOCALC itself is now quite forceful in telling the user what it expects. We hope this will make the learning experience easier, and reduce the likelihood of mistakes.
  • Modebox calculations now work.
  • Previously, only pseudosection and P-T projection calculations were thoroughly scripted, with other calculation facilities being largely interactive. There is now comprehensive scripting for our other currently-operational calculation facilities:
  • There is now documentation for dogmin (G-minimisation at a P-T coordinate) – a thoughtful guide by RP on the safest way to use this rather dangerous facility.
  • Much more has happened behind the scenes in version 3.50, aimed at making the code easier to maintain. These changes are mentioned in the release notes bundled with the software.

The THERMOCALC 3.50 executable is still called “tc350beta”, reminding us that some facilities aren’t working yet: µ-µ diagrams, and calculations involving charged aqueous species, are still to come.

Download the new software here.

We wish all our users a safe and happy holiday period, and some relaxation at the end of an extraordinary year.