Equilibrium dihedral angles in the system H2O-CO2-NaCl-calcite, and implications for fluid flow during metamorphism

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Authors:Holness, Marian B.; Graham, Colin M.
Author Affiliations:Primary:
University of Cambridge, Department Earth Sciences, Cambridge, United Kingdom
Other:
University of Edinburgh, United Kingdom
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 108(3), p.368-383. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1991
Note:In English. 61 refs.; illus.
Summary:Fluid-calcite-calcite dihedral angles have been measured for fluids in this system between 1 and 2 kbar, and 550-750 degrees C. It is found that the calcite-calcite-H2O dihedral angle decreases steadily with addition of NaCl from 80 degrees (pure water) to 44 degrees (60 wt.% NaCl). The CO2-H2O system displays a well-defined minimum at XCO2 = 0.5, with a dihedral angle of 50 degrees . Experiments with fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the CO2-H2O-NaCl system, which can be approximately correlated with the compositions of the two fluid phases. Such bimodality was only observed for immiscible fluids in the H2O-NaCl system if the quench rate exceeded approx 200 degrees C/min. The fluid phase topology in devolatilizing marbles will only be a connected network for very saline brines and fluids with XCO2 close to 0.5. Fluids trapped in fluid inclusions in calcite grains in marbles may be mainly H2O- or CO2- rich, and of low salinity. All other fluid compositions in the H2O-CO2-NaCl-calcite system will occupy isolated pores, the largest of which will grow at the expense of the smallest. Escape of fluid produced in devolatilization reactions in such conditions will occur by fluid overpressuring and hydrofracture. In contrast previous studies predict that quartz- dominated lithologies will permit pervasive flow of H2O-NaCl fluids, but not of H2O-CO2 fluids. Examples supporting these results are discussed. [R.E.S.]
Subjects:Calcite; Carbonates; Crystal chemistry; Fluid inclusions; Immiscibility; Inclusions; Isotope ratios; Isotopes; Metamorphism; O-18/O-16; Oxygen; P-T conditions; Phase equilibria; Stable isotopes; H<2`O-CO<2`-NaCl-calcite
Abstract Numbers:92M/1558
Record ID:1993010556
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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040 |a ViAlAGI  |c ViAlAGI 
072 7 |a 05A  |2 georeft 
100 1 |a Holness, Marian B.  |e analytic author  |u University of Cambridge, Department Earth Sciences, Cambridge 
245 1 0 |a Equilibrium dihedral angles in the system H<2`O-CO<2`-NaCl-calcite, and implications for fluid flow during metamorphism 
300 |a p. 368-383 
500 |a In English. 61 refs. 
500 |a Abstract number: 92M/1558 
500 |a Abstractor: R.E.S. 
500 |a Affiliation: University of Cambridge, Department Earth Sciences; Cambridge; GBR; United Kingdom 
500 |a Affiliation: University of Edinburgh; ; GBR; United Kingdom 
500 |a Key title: Contributions to Mineralogy and Petrology 
500 |a Source note: Contributions to Mineralogy and Petrology, 108(3), p.368-383. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999 
500 |a Publication type: journal article 
504 |b 61 refs. 
510 3 |a GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom 
520 |a Fluid-calcite-calcite dihedral angles have been measured for fluids in this system between 1 and 2 kbar, and 550-750 degrees C. It is found that the calcite-calcite-H<2`O dihedral angle decreases steadily with addition of NaCl from 80 degrees (pure water) to 44 degrees (60 wt.% NaCl). The CO<2`-H<2`O system displays a well-defined minimum at XCO<2` = 0.5, with a dihedral angle of 50 degrees . Experiments with fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the CO<2`-H<2`O-NaCl system, which can be approximately correlated with the compositions of the two fluid phases. Such bimodality was only observed for immiscible fluids in the H<2`O-NaCl system if the quench rate exceeded approx 200 degrees C/min. The fluid phase topology in devolatilizing marbles will only be a connected network for very saline brines and fluids with XCO<2` close to 0.5. Fluids trapped in fluid inclusions in calcite grains in marbles may be mainly H<2`O- or CO<2`- rich, and of low salinity. All other fluid compositions in the H<2`O-CO<2`-NaCl-calcite system will occupy isolated pores, the largest of which will grow at the expense of the smallest. Escape of fluid produced in devolatilization reactions in such conditions will occur by fluid overpressuring and hydrofracture. In contrast previous studies predict that quartz- dominated lithologies will permit pervasive flow of H<2`O-NaCl fluids, but not of H<2`O-CO<2` fluids. Examples supporting these results are discussed. 
650 7 |a Calcite  |2 georeft 
650 7 |a Carbonates  |2 georeft 
650 7 |a Crystal chemistry  |2 georeft 
650 7 |a Fluid inclusions  |2 georeft 
650 7 |a Immiscibility  |2 georeft 
650 7 |a Inclusions  |2 georeft 
650 7 |a Isotope ratios  |2 georeft 
650 7 |a Isotopes  |2 georeft 
650 7 |a Metamorphism  |2 georeft 
650 7 |a O-18/O-16  |2 georeft 
650 7 |a Oxygen  |2 georeft 
650 7 |a P-T conditions  |2 georeft 
650 7 |a Phase equilibria  |2 georeft 
650 7 |a Stable isotopes  |2 georeft 
653 |a H<2`O-CO<2`-NaCl-calcite 
700 1 |a Graham, Colin M.,  |e analytic author  |u University of Edinburgh 
773 0 |t Contributions to Mineralogy and Petrology  |d Heidelberg-New York : Springer International, Sep. 1991  |x 0010-7999  |y CMPEAP  |n Contributions to Mineralogy and Petrology, 108(3), p.368-383. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999 Publication type: journal article  |g Vol. 108, no. 3  |h illus.