isenthalpic assimilation of CO2-only fluid

[sbutami]

Dear all,

I am currently attempting to model assimilation of a fluid comprising only of CO2 into a hydrous basaltic andesite melt (~56 wt. % SiO2) using rhyolite-MELTS v.1.2.0, but rhyolite-MELTS keep aborting at even the lowest addition of CO2 only fluid (I tried adding 1-5g of fluids). I am setting the temperature of the incoming fluid at liquidus T, which is higher than my resident melt (1000Ã,°C).

Having followed the tutorial with MORB melt, I managed to model it successfully but am wondering about differences in the sequence of steps taken to model assimilation of fluids vs solids. Therefore, may I ask how to go about modelling (isenthalpic) assimilation of pure CO2 fluid into hydrous magma? What are the pitfalls for assimilation processes of fluids into magma and how can I prevent MELTS calculations from aborting? Your advice is appreciated. Thank you. Sri

[asimow]

Dear Sri,

I tried this calculation (with my own basaltic andesite composition that I had sitting around) and it worked just fine. For the record, the result of adding 5g of CO2 at 1200Ã,°C to 100g melt at 1200Ã,°C isenthalpically is to lower the temperature by 0.35 Ã,°C (i.e. the enthalpy of mixing is positive).

Try saving the .melts file content below as a .melts file. Launch the MELTS GUI, choose rhyoliteMELTS 1.2, open the file, and execute (you may have to halt it after a moment to it doesn't keep cycling the last equilibrium state forever). If that works, then you can try modifying this .melts file to match your particular calculation.

I realize that doesn't exactly tell you what you should have done differently, but hopefully it will get you going.

-- P

BA_CO2.melts:
Title: basalticandesite
Initial Composition: SiO2 54.8600
Initial Composition: TiO2 0.7700
Initial Composition: Al2O3 18.7800
Initial Composition: Fe2O3 1.0000
Initial Composition: FeO 8.0600
Initial Composition: MnO 0.2100
Initial Composition: MgO 3.6600
Initial Composition: CaO 8.8000
Initial Composition: Na2O 3.0800
Initial Composition: K2O 0.7800
Initial Composition: P2O5 0.1400
Initial Composition: H2O 1.0000
Initial Composition: CO2 0.0000
Initial Temperature: 1200.00
Final Temperature: 0.00
Initial Pressure: 3000.00
Final Pressure: 30000.00
Increment Pressure: 0.00
Increment Enthalpy: 0.00
dp/dH: 0.00
log fo2 Path: None
Mode: Isenthalpic
Assimilant: Temperature 1200.00
Assimilant: Mass 5.00
Assimilant: Increments 1.00
Assimilant: Liquid Mass 0.00
Assimilant: Units Wt %
Assimilant: fluid 100.00
Assimilant: h2oduan 0.00
Assimilant: co2duan 100.00