An H2O-CO2 mixed fluid saturation model compatible with rhyolite-melts. Mark S. Ghiorso and Guilherme A.R. Gualda

Transcription

1 An H2O-CO2 mixed fluid saturation model compatible with rhyolite-melts Mark S. Ghiorso and Guilherme A.R. Gualda

2 Models already exist Why another model? Papale et al. (26), Duan (214) and a host of others More data and additional motivation Data on mixed H2O-CO2 fluid saturation in silicate melts has doubled since 26 New composition and temperature, pressure regimes have been explored. No existing model is internally consistent with melt-solid thermodynamic data/model collections (e.g., MELTS) Interesting issues Can a model be constructed that is applicable to higher pressure (current models are limited to ~ 1 GPa)? Existing and widely used models do not include H2O, OH speciation or CO2, CO3 = speciation. Are these species required? What new data are necessary to make these models more robust to extrapolation

3 Na 2 O+K 2 O wt% (anhydrous) H2O Jd Ab Na 2 O+K 2 O wt% (anhydrous) CO2 Ne Jd Brey, G. (1976) Brooker, R.A., Kohn, S.C., Holloway, J.R., McMillan, P.F. (21) Brooker, R.A., Kohn, S.C., Holloway, J.R., McMillan, P.F., Carroll, M.R. (1999) King, P.L., Holloway, J.R. (22) Mattey, D.P. (1991) Mattey, D.P., Taylor, W.R., Green, D.H., Pillinger, C.T. (199) Morizet, Y., Brooker, R.A., Kohn, S.C. (22) Pan, V., Holloway, J.R., Hervig, R.L. (1991) Pawley, A.R., Holloway, J.R., McMillan, P.F. (1992) Rai, C., Sharma, S.K., Muenow, D.W., Matson, D.W., Byers, C.D. (1983) Roach, A.L. (25) Thibault, Y., Holloway, J.R. (1994) Ab 5 3 Fo Di SiO 2 wt% (anhydrous) Fo Di SiO 2 wt% (anhydrous) Behrens, H., Misiti, V., Freda, C., Vetere, F., Botcharnikov, R.E., Scarlato, P. (29) Behrens, H., Ohlhorst, S., Holtz, F., Champenois, M. (24) Na 2 O+K 2 O wt% (anhydrous) H2O-CO2 Blank, J.G., Stolper, E.M., Carroll, M.R. (1993) Botcharnikov, R., Freise, M., Holtz, F., Behrens, H. (25) Botcharnikov, R.E., Behrens, H.,Holtz, F. (26) Botcharnikov, R.E., Holtz, F., Behrens, H. (27) Dixon, J.E., Stolper E.M., Holloway, J.R. (1995) Iacono-Marziano, G., Norizet, Y., Le Trong, E., Gaillard, F. (212) Iacovino, K., Moore, G., Roggensack, K., Oppenheimer, C., Kyle, P. (213) Jakobsson, S. (1997) King, P.L., Holloway, J.R. (22) Lesne, P., Kohn, S.C., Blundy, J., Witham, F., Botcharnikov, R.E., Behrens, H. (211) Lesne, P., Scaillet, B., Pichavant, M., Beny, J-M. (211) Morizet, Y., Paris, M., Gaillard, F., Scaillet, B. (21) Shishkina, T.A., Botcharnikov, R.E., Holtz, F., Almeev, R.R., Jazwa, A.M., Jakubiak, A.A. (214) Shishkina, T.A., Botcharnikova, R.E., Holtz, F., Almeeva, R.R., Portnyagin, M.V. (21) Tamic, N., Behrens, H., Holtz, F. (21) Vetere, F., Botcharnikov, R.E., Holtz, F., Behrens, H., de Rosa, R. (211) Vetere, F., Holtz, F., Behrens, H., Botcharnikov, R.E., Fanara, S. (214) Model construction: Data Solubility of H2O in silicate melts (on assumption of pure water fluid) Solubility of CO2 in silicate melts Saturation conditions for mixed H2O-CO2 fluids SiO 2 wt% (anhydrous)

4 2 H2O 3 25 CO P (MPa) 1 P (MPa) T ( o C) T ( o C) 3 1 H2O-CO2 25 solubility experiments O solubility experiments Fluid saturation experiments 8 2 P (MPa) 6 P (MPa) T ( o C) T ( o C)

5 Thermodynamic model: melt phase (regular associated solution, after MELTS)! #! Independent Component!! or Basis Species!!! SiO2!!!! Molar Gibbs free energy: o G = X i µ i + RT X i ln X i + RT X ln X + 1 X H2 O O ( O )ln( 1 X H2 O ) i= i= Condition of internal or homogeneous equilibrium: i= j= W ij X i X j 1! TiO2!!!! 2! Al2O3!!!! 3! Fe2O3!!!! 4! Cr2O3!!!! 5! Fe2SiO4!!! 6! MnSi½O2!!! 7! Mg2SiO4!!! o = µ SiO2 o µ CaSiO3 o µ CO2 o + µ CaCO3 ( ) X i + RT ln X SiO 2 X CaCO3 + W X CaSiO3 X W W + W SiO2, j CaSiO 3, j, j CaCO 3, j CO2 i= 8! NiSi½O2!!! 9! CoSi½O2!!! 1! CaSiO3!!!! Chemical potential of nonvolatile melt components and of CO2: o µ SiO2 = µ = µ SiO2 Chemical potential of H2O: µ = µ = µ o H2 O 14 O + RT ln X SiO2 + RT ln 1 X H2 O 2 + RT ln X H2 O ( ) + W SiO2,iX i 1 2 i= + W X H2 O,j j 1 2 j= i= j= i= W ij X i X j j= W ij X i X j 11! Na2SiO3!!! 12! KAlSiO4!!! 13! Ca3(PO4)2!!! 14! H2O!!!! 15! CO2!!!!! Dependent Species!!! CaCO3!!!! Thermodynamic model: H2O-CO2 mixed fluid phase (virial EOS of Duan and Zhang, 26)

6 Basalt and Basaltic Andesite Andesite and Dacite 9 9 O wt% (model) 6 O wt% (model) O wt% (measured) O wt% (measured) 15 Rhyolite Fitting the model: 12 Equate chemical potentials of the H2O component in melt and fluid O wt% (model) 9 6 Optimize both standard state properties and interaction parameters for H2O in the melt 3 Singular Value analysis O wt% (measured) Model-Data recovery: H2O

7 12 Trachybasalt, Basaltic trachyandesite Basanite, Tephrite, Phonotephrite 9 Trachyandesite, Trachyte, Trachydacite Tephriphonolite, Phonolite 9 O wt% (model) 6 O wt% (model) O wt% (measured) O wt% (measured) 3 Not natural and not albite 3 8 O wt% (model) 2 O wt% (model) T o C P MPa 1 1 NaAlSi 3 O 8 liquid O wt% (measured) O wt% (measured)

8 Fitting the model: Equate chemical potentials of the CO2 component in melt and fluid Optimize both standard state properties and interaction parameters for CO2 in the melt. Because of the speciation, the optimization is non-linear. Singular Value analysis is used at each non-linear step to the residual minimum wt% (model) Model-Data recovery: CO wt% (measured)

9 Inferred carbon speciation in mixed fluid systems: 15 Chemical potential residual (kj) mafic /( +CaCO 3 ) rhyolitic

10 Model recovery in rhyolitic systems: Tamic, N., Behrens, H., Holtz, F. (21) - 11 o C.3 P = 2 P = 5.25 wt% O wt%

11 Model prediction in rhyolitic systems at high pressure: Duncan, M.S., Dasgupta, R. (214) o C 1.2 wt% P (GPa)

12 Application: melt inclusions in quartz Rhyolite (Bishop Tuff) wt% X O fluid O wt%

13 85 C Application: constraining % crystallization and initial fluid composition using a Monte Carlo analysis (wt. %) % Solids O (wt. %) O (wt. %) 2.74 O O.1 (wt. %) O (wt. %) 2.74 wt. % O 3.24 wt. % O 3.74 wt. % O 4.24 wt. % O 4.74 wt. % O 75 C Late Bishop Tuff Avg. glass inclusion % Solids (wt. %) 1. Specify a melt inclusion composition 2. Select a pressure 3. Generate a set of model compositions with a range of H2O/CO2 contents. 4. Correlate model outcomes to fluid H2O, CO2 concentrations 5. Result should be internally consistent with additional observations like phenocryst content of erupted magma. 6. If not return to 2 7. If inclusion is not primary, the simulations may not converge to a self consistent answer.

14 fluid mole fraction melt ppm MORB, fluid saturated, equilibrium crystallization olv cpx.6 melt.4.4 O CO spn plg 5 liq 4 O.5 1. melt fraction melt wt % Application: evolution of H2O/CO2 ratio in melt as a consequence of crystallization fluid saturated; initial bulk composition 3:1 CO2:H2O equilibrium crystallization melts CO2 concentration is mainly a function of Fe-and silica-concentration Future directions: 1 5 melt wt % 15 Al 2 O 3 FeO fld SiO 2 /3 MgO Na 2 O T o C CaO reduced carbon fluids addition of solutes to the fluid phase extension to higher pressure as experimental data become available

15 MORB, fluid saturated, fractional crystallization solid: no fluid, dashed: with fluid fluid mole fraction cpx melt O olv.2.2 melt fraction 8. spn 2.5 melt ppm O cpx liq melt wt % SiO 2 /3 Al 2 O 3 melt wt % 15 1 FeO fld CaO MgO 5 Na 2 O T o C

16 12.# 1.# Anor 8.# Qtz Alk+Anor 6.# San+ Qtz+ plag 4.# 2.#.# 71# 72# 73# 74# 75# 76# 77# 78# 79# rhyolite5melts# rmelts#+#co2,#orig#h2o# rmelts#+#co2,#new#h2o#