# Understanding rhyolite-MELTS versions

**rhyolite-MELTS + H**_{2}O-CO_{2} fluid (v 1.2.x)

_{2}O-CO

_{2}fluid (v 1.2.x)

This version is a replacement and upgrade from rhyolite-MELTS 1.0.x. It is the rhyolite-MELTS model with water properties completely replaced with the H_{2}O-CO_{2} fluid saturation model of Ghiorso and Gualda (2015). Thermodynamic properties of the fluid phase are calculated from the model of Duan and Zhang (2006). Use this version to model crystallization in bulk compositions other than those that saturate in quartz and crystallize to the two-feldspar-, quartz-, fluid-saturated ternary minimum.

Cite as Gualda et al., 2012, and as Ghiorso and Gualda, 2015.

**rhyolite-MELTS + H**_{2}O-CO_{2} fluid (v 1.1.x)

_{2}O-CO

_{2}fluid (v 1.1.x)

Use this version ONLY to model crystallization in bulk compositions that saturate in quartz and crystallize to the two-feldspar-, quartz-, fluid-saturated ternary minimum. This version is the rhyolite-MELTS model with CO_{2} melt properties and mixed-fluid energetic terms from Ghiorso and Gualda (2015), utilizing H_{2}O melt properties and H_{2}O-anhydrous component energetic mixing terms from MELTS (which are the same as in rhyolite-MELTS v 1.0.x). Thermodynamic properties of the fluid phase are calculated from the model of Duan and Zhang (2006).

Cite as Gualda et al., 2012, and as Ghiorso and Gualda, 2015 (water model from Ghiorso and Sack, 1995).

**rhyolite-MELTS (original, v 1.0.x)**

This version is the MELTS model (Ghiorso and Sack, 1995) with corrections to the free energies of quartz and sanidine so that the eutectic-like crystallization at the ternary minimum in the quartz-two-feldspar+fluid system is recovered. (This version replaces MELTS, which should no longer be used to calculate phase relations in magmatic systems.) Use this version to model crystallization in natural composition liquids at pressures below 2 GPa. The fluid phase is modeled as pure H_{2}O. PhasePlot implements the rhyolite-MELTS model.

Cite as Gualda et al., 2012.

**Citations:**

Gualda G.A.R., Ghiorso M.S., Lemons R.V., Carley T.L. (2012) Rhyolite-MELTS: A modified calibration of MELTS optimized for silica-rich, fluid-bearing magmatic systems. Journal of Petrology, 53, 875-890.

Ghiorso M.S. and Gualda, G.A.R. (2015) An H_{2}O-CO_{2} mixed fluid saturation model compatible with rhyolite-MELTS. Contributions to Mineralogy and Petrology 2015, in press.

**Duan** Z. and **Zhang** Z. (2006) Equation of state of the H_{2}O, CO_{2}, and H_{2}O–CO_{2} systems up to 10 GPa and 2573.15 K: Molecular dynamics simulations with ab initio potential surface. Geochimica et Cosmochimica Acta, **70**, 2311–2324.