Separation of salts NaCl and CaCl2 in aqueous-carbon dioxide deep fluids

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Abstract

The possibility of changing the ratio of the concentrations of NaCl and CaCl2 salts in fluid phases formed as a result of heterogenization of the H2O–CO2–NaCl–CaCl2 fluid with a decrease in P-T parameters has been studied. A well-known experimental fact regarding the ternary systems H2O–CO2–NaCl and H2O–CO2–CaCl2 is the greater tendency of the H2O–CO2–CaCl2 system to separate into coexisting predominantly aqueous-salt and aqueous-carbon dioxide phases compared to the similar system H2O–CO2–NaCl. This experimental fact can be interpreted as a greater affinity of NaCl for CO2 compared to CaCl2. Using a recently developed numerical thermodynamic model of the H2O–CO2–NaCl–CaCl2 quaternary fluid system, it was possible to identify geologically significant consequences of this difference in the interaction of NaCl and CaCl2 with CO2. Multistage heterogenization of the H2O–CO2–NaCl–CaCl2 fluid with a significant decrease in P-T parameters ultimately leads to the formation of aqueous-carbon dioxide fluid phase f2, the salt component of which is significantly enriched in NaCl and depleted in CaCl2 compared to the initial fluid. The fluid phase f1 formed at each stage of heterogenization has a predominantly water-salt composition with the ratio of the mole fractions of NaCl and CaCl2 salts, differing little from that in the initial fluid. However, the total mole fraction of salt in the f1 phase, as a rule, significantly exceeds that in the original fluid. The density of phase f1 significantly exceeds the density of phase f2. During the process of multistage heterogenization of the fluid phase f1, there is no formation of a fluid with a significant enrichment of CaCl2 compared to the initial ratio of the mole fractions of NaCl and CaCl2. At the same time, successive multiple separation of the f2 phase leads to the enrichment of its salt component in NaCl. Under favorable conditions, this process can lead to the formation of a fluid with almost pure NaCl salt. Changes in the salt composition of the fluid H2O–CO2–NaCl–CaCl2 are considered in application to the evolution of fluid composition along the regressive branch of the P-T trend of HP metamorphism and syngranulite metasomatism in the Lapland granulite belt.

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About the authors

Mikhail V. Ivanov

Institute of Precambrian Geology and Geochronology RAS

Author for correspondence.
Email: m.v.ivanov@ipgg.ru
Russian Federation, Sankt-Peterburg

Sergei A. Bushmin

Institute of Precambrian Geology and Geochronology RAS

Email: s.a.bushmin@ipgg.ru
Russian Federation, Sankt-Peterburg

References

  1. Aranovich L.Y., Newton R.C. H2O activity in concentrated NaCl solutions at high pressures and temperatures measured by the brucite – periclase equilibrium // Contrib. Mineral. Petrol. 1996. V. 125. P. 200–212.
  2. Aranovich L.Y., Newton R.C. H2O activity in concentrated KCl and KCl-NaCl solutions at high temperatures and pressures measured by the brucite-periclase equilibrium // Contrib. Mineral. Petrol. 1997. V. 127. P. 261–271.
  3. Aranovich L.Y., Shmulovich K.I., Fed’kin V.V. The H2O and CO2 regime in regional metamorphism // Int. Geol. Rev. 1987. V. 29. P. 1379–1401.
  4. Bischoff J.L., Rosenbauer R.J., Fournier R.O. The generation of HCl in the system CaCl2-H2O: Vapor-liquid relations from 380–500°C // Geochim. Cosmochim. Acta. 1996. V. 60. P. 7–16.
  5. Frantz J.D., Popp R.K., Hoering T.C. The compositional limits of fluid immiscibility in the system H2O–CO2–NaCl as determined with the use of synthetic fluid inclusions in conjunction with mass spectrometry // Chem. Geol. 1992. V. 98. P. 237–255.
  6. Heinrich W., Churakov S.S., Gottschalk M. Mineral-fluid equilibria in the system CaO-MgO-SiO2-H2O-CO2-NaCl and the record of reactive fluid flow in contact metamorphic aureoles // Contrib. Mineral. Petrol. 2004. V. 148. P. 131–149.
  7. Johnson E.L. Experimentally determined limits for H2O–CO2–NaCl immiscibility in granulites // Geology. 1991. V. 19. P. 925–928.
  8. Manning C.E. Fluids of the lower crust: deep is different // Annu. Rev. Earth Planet. Sci. 2018. V. 46. P. 67–97.
  9. Manning C.E., Aranovich L.Y. Brines at high pressure and temperature: thermodynamic, petrologic and geochemical effects // Precambr. Res. 2014. V. 253. P. 6–16.
  10. Markl G., Bucher K. Composition of fluids in the lower crust inferred from metamorphic salt in lower crustal rocks // Nature. 1998. V. 391. P. 781–783.
  11. Shmulovich K.I., Graham C.M. An experimental study of phase equilibria in the system H2O–CO2–NaCl at 800°C and 9 kbar // Contrib. Mineral. Petrol. 1999. V. 136. P. 247–257.
  12. Shmulovich K.I., Graham C.M. An experimental study of phase equilibria in the systems H2O–CO2–CaCl2 and H2O–CO2–NaCl at high pressures and temperatures (500–800°C, 0.5–0.9 GPa): geological and geophysical applications // Contrib. Mineral. Petrol. 2004. V. 146. P. 450–462.
  13. Trommsdorff V., Skippen G., Ulmer P. Halite and sylvite as solid inclusions in high-grade metamorphic rocks // Contrib. Mineral. Petrol. 1985. V. 89. P. 24–29.
  14. Zhang Y.-G., Frantz J.D. Experimental determination of the compositional limits of immiscibility in the system CaCl2-H2O-CO2 at high temperatures and pressures using synthetic fluid inclusions // Chem. Geol. 1989. V. 74. P. 289–308.

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2. Fig. 1. (a) Solvuses of the H2O–CO2–NaCl–CaCl2 fluid system at different ratios of the molar fractions of NaCl and CaCl2 in the salt part of the system at T = 500°C, P = 1 kbar and T = 1100°C, P = 14 kbar. (b) The effect of salt dissociation on the phase state of the fluid. Solid bold lines are solvuses of the edge systems H2O–CO2–NaCl and H2O–CO2–CaCl2. A solid thin line is the boundary of the field of the presence of solid NaCl in the H2O–CO2–NaCl system. The dotted lines are the same under the assumption that there is no dissociation of NaCl and CaCl2 molecules. Fields: 1 – homogeneous fluid, 2 – stratified fluid, 3 – stratified fluid coexisting with solid NaCl in the H2O–CO2–NaCl system.

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3. Fig. 2. (a) Phase diagram in the coordinates H2O–CO2–salt. Curved lines – solvuses: T = 1000°C, P = 12 kbar, rNaCl = 0.5 – blue bold line; T = 500°C, P = 2 kbar, rNaCl = 0.99 – green thin line; T = 500°C, P = 2 kbar, rNaCl = 0.79 – orange dotted line the line. (b) Successive stages of heterogenization of the primary fluid and secondary fluid phases. (c) Evolution of the salt composition of phase f2. The green solid lines represent the relative NaCl content in the salt component of phase f2 and the residual number of moles of phase f2 relative to the number of moles of the primary fluid. The orange dotted lines are the same for phases of type f1 separating from the primary fluid and phase f2 at the next stages of heterogenization. (d) The densities of phase f2 and separating phases of type f1. (e) The ratio rNaCl = XNaCl/ xsalt for phase f1 and the residual number of moles of phase f1 relative to the number of moles of the primary fluid. (e) The total salinity of phases f1 and f2.

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4. Fig. 3. Restoration of the complete composition of the fluid according to the composition of its water-salt component. Bold lines are solvuses for the compositions of the salt component in natural inclusions A and B at the upper point of the regressive P-T trend. Dotted lines are the lines of constant salinity of the water-salt part sH2O = xsalt/(xH2O + xsalt) corresponding to the composition of inclusions A and B. The mugs correspond to the complete fluid compositions on the solvus with the corresponding measured sH2O and rNaCl.

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5. Fig. 4. Evolution of the physico-chemical properties of the H2O–CO2–NaCl–CaCl2 fluid during movement along the regressive branch of the P-T trend of the evolution of HP granulites and singranulite infiltration metasomatites of the Lapland granulite belt (on the example of the Poryegub tectonic cover). The initial fluid with a predominance of CaCl2. (a) – evolution of phase f2, (b) – density of phase f2 and separating phases of type f1, (c) – evolution of phase f1.

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6. Fig. 5. Evolution of the physico-chemical properties of the H2O–CO2–NaCl–CaCl2 fluid during movement along the regressive branch of the P-T trend of the evolution of HP granulites and singranulite infiltration metasomatites of the Lapland granulite belt (on the example of the Poryegub tectonic cover). The initial fluid with a predominance of NaCl. (a) – evolution of phase f2, (b) – density of phase f2 and separating phases of type f1, (c) – evolution of phase f1.

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