The HPx-eos families

The following sets of HPx-eos are currently available:

  • Metapelite set (White et al, 2014): use for equilibria in typical metapelite bulk compositions at < 15 kbar (or cautiously at < 20 kbar).
  • Metabasite set (Green et al, 2016), used with ds62: equilibria in typical metabasite bulk compositions at < 20 kbar (or cautiously at < 30 kbar).
  • Igneous set (Holland et al, 2018), used with ds633: partial melting equilibria involving basaltic through to granitic melt compositions, excluding equilibria involving very alkaline magmas, omphacitic or jadeitic pyroxene. Dry peridotite melting calculations are calibrated up to ~60 kbar; calculations in hydrated systems are limited to pressures below 20 kbar (or 30 kbar with caution) by the large uncertainties associated with dissolution of silicates in aqueous fluids.

The various HPx-eos sets have a number of x-eos in common. However, each set contains some HPx-eos contain x-eos that were calibrated specifically for that set, using what was at the time the latest version of the underlying Holland & Powell dataset. It’s therefore advisable to use them in their sets, with the appropriate version of the dataset – the results of mixing and matching could be unexpected (or the dataset might not contain all the necessary end-members!).

For some phases, there are multiple x-eos available – sometimes even within the same HPx-eos set. A notorious examples is clinopyroxene (cpx): there are two x-eos for cpx in the metabasite set, one for sodic-calcic cpx that allows omphacite-like order-disorder at low temperatures, and one for high-temperature calcic cpx with significant tetrahedral Al. A third cpx model is found in the newer igneous set of HPx-eos. Ultimately, we will aim to develop a library of models in which there is one HPx-eos per phase (Simon Schorn is currently working with Eleanor on a fiendishly complex single cpx). But for now, the different calibrations reflect the different contexts in which the models are to be used, and consequently different choices made during development.

The igneous set of HPx-eos will be used as the basis of futher model development. In principle it could already be used, cautiously, to replace the two older sets of HPx-eos in many cases, although the main focus of its calibration was peridotite melting and haplogranite equilibria.

We’re always grateful to be told about any surprising results that users obtain with the HPx-eos!