**alphaMELTS 2.3 standalone & for MATLAB/Python** is now open source and available on GitHub (https://github.com/magmasource/alphaMELTS).**alphaMELTS 1.9** is available at the legacy download and information site.

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#91

Hello,

I am working on a project investigating the crystallization of Mercury's magma ocean, and was hoping for some guidance on how to use MELTS to that end. The issue that I am having is the extreme reducing conditions and odd composition of the magma. I have my starting composition based off of the Indarch meteorite (from Berthet et al. 2009) and was going to remove silicon from the composition at varying levels to simulate the Si being partitioned into the core. I am unable to run any calculations past finding the liquidus which is much lower temp than I would expect (around 678 C). When I attempt to execute I get a SiO2 has a negative mole fraction, and as I've looked through the forum I have not found a solution as of yet.

Any help would be greatly appreciated!

wt. %.

SiO2 - 38.67

MgO - 49.22

Al2O3 - 4.08

CaO - 2.68

Na2O - 2.84

K2O - 0.31

Cr203 - 1.32

MnO - 0.70

TiO2 - 0.17

Temp was 1800 C to 1400 C

Pressure was 2.5 GPa to 1.0 GPa

fO2 (IW) was -4.93 from computing the redox state.

The system crashes at any attempt to execute past finding the liquidus.

Thanks again for any help!

Cheers,

Richard Gwyn

gwynr@wwu.edu

I am working on a project investigating the crystallization of Mercury's magma ocean, and was hoping for some guidance on how to use MELTS to that end. The issue that I am having is the extreme reducing conditions and odd composition of the magma. I have my starting composition based off of the Indarch meteorite (from Berthet et al. 2009) and was going to remove silicon from the composition at varying levels to simulate the Si being partitioned into the core. I am unable to run any calculations past finding the liquidus which is much lower temp than I would expect (around 678 C). When I attempt to execute I get a SiO2 has a negative mole fraction, and as I've looked through the forum I have not found a solution as of yet.

Any help would be greatly appreciated!

wt. %.

SiO2 - 38.67

MgO - 49.22

Al2O3 - 4.08

CaO - 2.68

Na2O - 2.84

K2O - 0.31

Cr203 - 1.32

MnO - 0.70

TiO2 - 0.17

Temp was 1800 C to 1400 C

Pressure was 2.5 GPa to 1.0 GPa

fO2 (IW) was -4.93 from computing the redox state.

The system crashes at any attempt to execute past finding the liquidus.

Thanks again for any help!

Cheers,

Richard Gwyn

gwynr@wwu.edu

#92

Thank you Paula. Problem solved.

#93

Hi,

It sounds like you need to set ALPHAMELTS_TRACE_INPUT_FILE to "default_trace_data.dat" so it reads in the file instead of using the built-in values.

Paula

It sounds like you need to set ALPHAMELTS_TRACE_INPUT_FILE to "default_trace_data.dat" so it reads in the file instead of using the built-in values.

Paula

#94

Hello,

I am using alphaMELTS 1.9 to model variations of major and trace element during melt-rock interaction. I want to sent my own partition coefficients for selected elements between cpx and melt. I unset the ALPHAMELTS_TRACE_DEFAULT_DPTX and changed the values in "default_trace_data.dat". Unfortunately, it doesn't appear to work that way. AlphaMELTS executable seems still keeping the default values. Should I have to make a new trace_data file? But How can I read these in?

I am using alphaMELTS 1.9 to model variations of major and trace element during melt-rock interaction. I want to sent my own partition coefficients for selected elements between cpx and melt. I unset the ALPHAMELTS_TRACE_DEFAULT_DPTX and changed the values in "default_trace_data.dat". Unfortunately, it doesn't appear to work that way. AlphaMELTS executable seems still keeping the default values. Should I have to make a new trace_data file? But How can I read these in?

#95

It depends how you are calculating *Cp* for the Berman model. Are you taking the *Cp* expressions from Berman & Brown (1985)? There are a couple of sources of discrepancy:

*G*_{mix}). The *Cp* of mixing is *Cp*_{mix} = - *T* *∂*^{2}G_{mix}/∂T^{2}

However, for feldspar and most of the other solution phases in MELTS models, the*Cp*_{mix} term is zero. See the following and the code for more details:

If you want to view the MELTS source code you should sign up for GitLab (gitlab.com) and write to Mark Ghiorso (ghiorso@ofm-research.org) with your GitLab username to request access.

For albite you need to accounting for Al-Si order / disorder. The approach used is described on page 498 of Berman (1988) and encoded in the albite.c file that is part of the MELTS source code.- Pure phases that include 2nd order transitions, such as the silica polymorphs, have slightly different Landau contributions to
*Cp*in Berman (1988), as compared to Berman & Brown (1985). The correction is implied by, but not discussed in, Berman (1988), and is also not mentioned in the MELTS papers.

However, for feldspar and most of the other solution phases in MELTS models, the

If you want to view the MELTS source code you should sign up for GitLab (gitlab.com) and write to Mark Ghiorso (ghiorso@ofm-research.org) with your GitLab username to request access.

#96

Thank you very much for your response. I was also checking on the mineral phases' Cp, and I don't quite get the same results using Berman (1985) model, most probably because this model accounts for the end members solid solutions. How is it computed for, for example, a "plagioclase1" with a not end-member albite composition? Meaning that it is not pure NaAlSi3O8, but this is the predominant composition.

Thank you very much!

Thank you very much!

#97

Is this alphaMELTS 1.9 or 2?

#98

Hello!

I'm running some fractional crystallisation simulations where I am interested in the cumulative mass of the fluid, solid and liquid at each step. I just wanted to check that selecting fractionate solids and fractionate fluids was the correct way to do this?

Thus far I have been using the Phase_mass_tbl output and calculating the cumulative masses of fluid/liquid(given anyway)/solids from there.

For FC of a basalt w 1 wt% H2O at 200 MPa through to a final mass of ~10g liquid (69 wt% SiO2), I am getting a total cumulative mass of fluid1 (i.e. adding up the mass in each step) =0.35g. To me this is quite low but it may be right hence why i wanted to double check with you first!

also the alphamelts manual refers to frac_water - is this used interchangeably with frac_fluids?

Thanks again,

Olivia

I'm running some fractional crystallisation simulations where I am interested in the cumulative mass of the fluid, solid and liquid at each step. I just wanted to check that selecting fractionate solids and fractionate fluids was the correct way to do this?

Thus far I have been using the Phase_mass_tbl output and calculating the cumulative masses of fluid/liquid(given anyway)/solids from there.

For FC of a basalt w 1 wt% H2O at 200 MPa through to a final mass of ~10g liquid (69 wt% SiO2), I am getting a total cumulative mass of fluid1 (i.e. adding up the mass in each step) =0.35g. To me this is quite low but it may be right hence why i wanted to double check with you first!

also the alphamelts manual refers to frac_water - is this used interchangeably with frac_fluids?

Thanks again,

Olivia

#99

The H2O model in rhyolite-MELTS 1.1.0 is the old one, same as rhyolite-MELTS 1.0.2 and the original MELTS model. How the thermodynamic properties of the H2O dissolved in the melt, including the Cp contribution, are calculated is described in the last paragraph of Ghiorso & Sack (1995):

However, unless you are trying to model the granite ternary minimum you should probably be using rhyolite-MELTS 1.2.0, which includes the updated water solubility model (Ghiorso & Gualda, 2015). See the MELTS decision tree:

https://melts.ofm-research.org/MELTS-decision-tree.html

Paula

Quote

Thermodynamic properties of the H20 component in molten silicate liquids are modeled following the method of Nicholls (1980; Ghiorso et al. 1983). We adopt his value for the reference state entropy (152.63 J/mol-K) and optimize a value of the reference enthalpy (-279.992 kJ/mol) to satisfy best the experimental data on water solubility discussed above. We modify Nicholls' (1980) function for the volume integral contribution to the molar Gibbs energy of dissolved H20 by subtracting the Gibbs energy of supercritical water tabulated by Robie et al. (1978) and adding the identical quantity from Berman (1988, see previous paragraphs). This insures the thermodynamic properties of the H20 component of Table AI are internally consistent with those of the supercritical fluid.

However, unless you are trying to model the granite ternary minimum you should probably be using rhyolite-MELTS 1.2.0, which includes the updated water solubility model (Ghiorso & Gualda, 2015). See the MELTS decision tree:

https://melts.ofm-research.org/MELTS-decision-tree.html

Paula

#100

Hello,

I am using alphaMELTS 2 with the rhyoliteMELTS 1.1.0 to make some numerical simulations. I wanted to know if (and how) the Cp of the melt phase is calculated, and how it takes into account the Cp of H2O dissolved. Checking on the papers I found that for the melt, the Cp is calculated by Lange & Navrosky (1992) model, but I don't know if this had being updated since to add the Cp of the water (for example, with the model of Bouhifd et al. (2006)).

Thank you very much!

I am using alphaMELTS 2 with the rhyoliteMELTS 1.1.0 to make some numerical simulations. I wanted to know if (and how) the Cp of the melt phase is calculated, and how it takes into account the Cp of H2O dissolved. Checking on the papers I found that for the melt, the Cp is calculated by Lange & Navrosky (1992) model, but I don't know if this had being updated since to add the Cp of the water (for example, with the model of Bouhifd et al. (2006)).

Thank you very much!