HPx-eos: igneous set

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General information

Citation: Holland, TJB, Green, ECR & Powell, R (2018). Melting of peridotites through to granites: a simple thermodynamic model in the system KNCFMASHTOCr. Journal of Petrology 59 881-900.


PhaseAlso in setsFirst published
silicate meltthis paper
aqueous fluidthis paper
plagioclase feldsparmetapelite, metabasiteHolland et al (2021) J Metam Geol DOI 10.1111/jmg.12639
spinel, Cr-spinel and magnetitethis paper
garnetthis paper
olivinethis paper
orthopyroxenethis paper
clinopyroxene and pigeonitethis paper
cordieritesomewhat reparameterised from White et al (2014) J Metamorph Geol 32 261-286
biotitesomewhat reparameterised from White et al (2014) J Metamorph Geol 32 261-286
muscovitemetapelite, metabasiteWhite et al (2014) J Metamorph Geol 32 261-286
epidotemetapelite, metabasiteHolland & Powell (2011) J Metamorph Geol 29 333-383
hornblendemetabasiteGreen et al (2016) J Metamorph Geol 34 845-892
ilmenitemetapelite, metabasiteWhite et al (2000) J Metamorph Geol 18 497-511

Use for: 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 igneous set will form the basis for future developments to the HPx-eos. In principle they can be used to replace the metapelite and metabasite sets in many contexts – if you’ve done a comparison between the two, we’d be very interested to hear about it.

Known issues:

  • (Orthopyroxene stability: although the HPx-eos for opx strictly spans a compositional space that is bounded by the diopside composition, users/implementers should keep the composition to XCaM2 < 0.5 to avoid the stability of a inappropriate high-Ca opx phase. — This problem should be solved in the new x-eos bundle from 31-10-2020.)
  • For peridotite melting (and other contexts?), the calculated mode of orthopyroxene is often much too large, in some cases twice the expected volumetric proportion.
  • Calculations with Perple_X indicate that small regions of multiple melt phase stability may occur near the solidus in peridotitic systems. If so, this is an unintended result, and we’d be glad to hear about it.
  • The clinoamphibole x-eos sometimes takes too much tetrahedral Al, resulting in < 6 Si p.f.u. on a 24-oxygen basis.
  • Are you aware of any other problems? Please let us know!

Full model details and benchmark calculations

Here we provide human-readable details of the igneous-set HPx-eos, along with benchmark calculations to allow implementations to be tested. Contact us if anything remains unclear.

Download full HPx-eos details for phases: silicate melt, aqueous fluid, plagioclase feldspar (Ibar1; Ca-rich), plagioclase feldspar (Cbar1; Na-rich; also used for potassium feldspar), olivine, muscovite, biotite, garnet, epidote, cordierite, orthopyroxene, clinopyroxene (also pigeonite), spinel (also Cr-spinel, magnetite), hornblende, ilmenite (current 23-01-2022):

End-members from dataset version: 6.33 (Fri 23 Jun, 2017)

Benchmarks, generated with THERMOCALC 3.50. These files don’t necessarily represent key (or necessarily most stable) equilibria; they are just to check implementation of the x-eos. Contact us if you need specific additional calculations for comparison and are unable to produce these yourself. Download here (current 31-10-2020):

Alternative Fig. 5 (RE46 basalt pseudosection) from the Holland et al (2018) paper. The published figure focuses on the 1 bar phase relations, and only extends these phase relations to higher pressure in an indicative sense, ignoring other phases that become stable at higher pressures. Due to feedback from users, Tim Holland has provided an alternative figure that shows the stable phase relations:

Download THERMOCALC input files

If you’re new to THERMOCALC, please begin by reading the THERMOCALC section of the website, and download the files below as directed in the Get started guide.

Download THERMOCALC input files/information for the igneous-set HPx-eos here (the current bundle is dated 23-01-2022):

  • dataset 6.33 input file tc-ds633.txt (Fri 23 Jun, 2017)
  • axfiles tc-ig47<system>.txt, formatted for THERMOCALC version 3.47, and tc-ig50<system>.txt, for version 3.50, in systems NCKFMASTOCr and NCKFMASHTOCr (these replace files in previous web distributions)
  • full descriptions of the x-eos, including definitions of mixing sites, end-members and compositional variables
  • samecoding information and a selection of starting guesses for compositional/order variables that might be suitable as a starting point for a calculation.

Alternatively you can download the full web distribution that accompanied the paper (updated Apr 2019) on Tim Holland’s software pages. This includes the fo2melt program and more examples relating to calculations in the paper; however the axfiles included are compatible with THERMOCALC 3.47 only

Information related to use with other software

In Perple_X: HPx-eos that are unique to the igneous set are labelled “(HGP)”. Jeff Moyen’s spreadsheet gives more information.

Please contact us if you think there is other information we should include here.