Hostname: page-component-78c5997874-mlc7c Total loading time: 0 Render date: 2024-11-19T04:36:45.224Z Has data issue: false hasContentIssue false
  • English
  • Français

Kinetic controls on the formation of metastable phases during the experimentally induced breakdown of chlorite

Published online by Cambridge University Press:  05 July 2018

K. A. Waldron ,
G. T. R. Droop  and
P. E. Champness
K. A. Waldron
Affiliation:
Department of Geology, The University of Manchester, Manchester M13 9PL, U.K.
G. T. R. Droop
Affiliation:
Department of Geology, The University of Manchester, Manchester M13 9PL, U.K.
P. E. Champness
Affiliation:
Department of Geology, The University of Manchester, Manchester M13 9PL, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

The kinetics and reaction mechanisms of chlorite breakdown have been studied in a series of experiments at conditions similar to those achieved during contact metamorphism (T = 600-725°C P = 1 kbar). Cores of chlorite schist were used as starting material in order to simulate natural metamorphic systems and preserve reaction textures. Reaction products were analysed by electron microprobe, scanning- and transmission-electron microscopy (SEM, TEM). Although the texture of the original chlorite was preserved in experiments run below 680°C talc had replaced chlorite. Olivine and spinel formed along grain boundaries, indicating long-range diffusion of aluminium. Above 680°C the chlorite was replaced by patches of disordered, aluminous pyroxene. Olivine and spinel grew both within the pyroxene and along what are believed to be former chlorite grain-boundaries. Reactions relevant to the observed textures and assemblages are:

Thermodynamic calculations show that both of these reactions are metastable in the FeO-MgO-Al2O3-SiO2-H2O system in the P-T range of our experiments. In addition, previous experimental studies and our calculations indicate that the stable reaction is:

The absence of cordierite in the run products, and the formation of talc and orthopyroxene while thermodynamically metastable, show that the ease of nucleation of these phases controlled the reaction mechanisms in the early stages.

Keywords

chlorite breakdownreaction mechanismskineticsmetastabletalcorthopyroxenespinelolivine
Type
Mineralogy
Information
Mineralogical Magazine , Volume 57 , Issue 386 , March 1993 , pp. 141 - 156
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1993

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Footnotes

*

Present address: Department of Geology, Colgate University, Hamilton, NY 13346, USA.

References

Bell, I. A. and Wilson, C.J.I. (1977) Growth defects in metamorphic biotite. Phys. Chem. Mineral., 2, 153–69.Google Scholar
Brcarlcy, A. J. (1986) An electron optical study of muscovite breakdown in pclitic xenoliths during pyrometamorphism. Mineral. Mag., 50, 385–97.Google Scholar
Brcarlcy, A. J. (1987a) A natural example of the disequilibrium breakdown of biotite at high temperature: TEM observations and comparison with experimental kinetic data. Ibid., 51, 93-106.Google Scholar
Brcarlcy, A. J. (1987b) An experimental and kinetic study of the breakdown of aluminous biotite at 800°C Reaction microstructurcs and mineral chemistry. Bull. Minr 110, 512–32.Google Scholar
Brcarlcy, A. J. and Ruble, D. C. (1990) The cffccts of H20 on the disequilibrium breakdown of muscovite + quartz. J. Petrol., 31, 925–56.Google Scholar
Brown, B. E. and Bailey, S. W. (1962) Chlorite polytypism: I. Regular and semi-random one-layer structures. Amer. Mineral., 47, 819–50.Google Scholar
Champness, P. E., (1970) Nucleation and growth of iron oxides in olivines. (Mg, Fe)2SiO4. Mineral Mag., 37, 790–800.Google Scholar
Chernosky, J. V. Jr. (1974) The upper stability of clinochlore at low pressure and the frec energy of formation of Mg-cordicrite. Amer. Mineral., 59, 496–507.Google Scholar
Cho, M. and Fawcett, J. J. (1986) A kinentic study of clinochlore and its high temperaturc equivalent forsteritc-cordierite-spinel. Ibid., 71, 68-77.Google Scholar
Droop, G. T. R. (1987) A general equation for estimating Fe+3 concentration in ferromagncsian silicates and oxides from microprobe analyses using stoichiometric criteria. Mineral. Mag., 51, 431–5.Google Scholar
Fawcett, J. J. and Yoder, H. S. (1966) Phase relation-ships of chlorite in the system MgO-AIzO3-SiO2-1120. Amer. Mineral., 51, 35, 3–87.Google Scholar
Fleming, P. D. and Fawcctt, J. J. (1976) Upper stability of chlorite + quartz in the system MgO-FcO-AI203-SiO2-H2O at 2 kbar water pressure. Ibid., 61, 1175-93.Google Scholar
Herzberg, C. T. (1983) The reaction forsterite + cordicrite — aluminous orthopyroxene + spinel in the system MgO-AI203-SiO2. Contrib. Mineral. Petrol., 84. 84-90.Google Scholar
Holland, T. J. B, and Powell, R. (1990) An enlarged and updated internally consistent thermodynamic datasct with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3Al2O3-TiO2-SiO-2-C-H2-O2. J. Metamorphic Geol., 8, 89–124.Google Scholar
Jenkins, D. M. and Chernosky, J. V. Jr. (1986) Phase equilibria and crystallochcmical properties of Mg-chlorite. Amer. Mineral.. 71, 924–36.Google Scholar
Kretz, R. (1983) Symbols for rock-forming minerals. Ibid., 68, 277-9.Google Scholar
McOnic, A. W.. Fawcett, J. J., Jeffrey, J., and James, R. S. (1975) The stability of intermediate chlorites of the clinochlore-daphnite series at 2 kbar PH2O 60, 1047-62.Google Scholar
Nelson, B.W. and Roy, R. (1958) Synthesis of the chlorites and their structural and chemical constitu-tion. Ibid., 43, 707-25.Google Scholar
Powell, R. and Holland, T. J. B. (1988) An internally consistent dataset with uncertainties and correlations: 3. Application to geobarometry, worked cxamples and a computer program. J. Metamorphic Geol., 6, 173–204.Google Scholar
Robie, R. A., Hemingway, B. S., and Fishcr, J. R. (1978) Thermodynamic properties of minerals and related substances at 298. 15 K and 1 bar (1(I5 pascals) pressure and at higher temperatures. United States Geol. Survey Bulletin, 1452.Google Scholar
Roy, D. M., and Roy, R. (1955) Synthesis and stability of minerals in the system MgO-Al2O3-SiO,-H,O. Amer. Mineral., 40, 147–78.Google Scholar
Ruble, D. C. and Brearley, A. J. (1987) Metastable melting during the breakdown of muscovite + quartz at 1 kbar. Bull. Minéal., 110, 533–49.Google Scholar
Ruble, D. C. and Brearley, A. J. (1991 submitted) Kinetics of partial melting of muscovite + quartz and rates of multicomponent diffusion in H2O-saturated granitic liquid. Geochim. Cosrnochim. Acta. Google Scholar
Seiferl, F. (1974) Stability of sapphirine: a study of the aluminous part of the system MgO-Al203-SiO21120. J. Geol., 82, 173–204.Google Scholar
Velde, B. (1973) Phasc equilibria in the system MgOAl3O3-SiO2-H2O: chlorites and associated minerals. Mineral lag., 39, 297–312.Google Scholar
Wirth, R. (1986) Thermal alteration of glaucophane in the contact aureole of the Traversella Intrusion (N. Italy). Neus. Jahrb. Min. Abh., 154, 193–205.Google Scholar
Wood, B. J. and Banno, S. (1973) Garnet-orthopyroxenc and orthopyroxene-clinopyroxene relationships in simple and complcx systems. Contrib. Mineral. Petrol., 42, 109–24.Google Scholar
Worden, R. H., Champness, P. E. and Droop, G. T. R. (1987) Transmission electron microscopy of pyromctamorphic breakdown of phengite and chlorite. Mineral. Mag., 51, 107–21.Google Scholar
Worden, R. H., Champness, P. E. and Droop, G. T. R. (1988) Mechanisms of thermal decomposition of sheet silicates in rocks. Proc. Intl. Conf on Phase Transformation, Cambridge, 1987, Inst. Metals, 614-17.Google Scholar
Worden, R. H., Champness, P. E. and Droop, G. T. R. Droop, G. T. R. and Champness, P. E. (1992) The influence of crystallography and kinetics on phengite breakdown reactions in a low-pressure metamorphic aureole. Contrib. Mineral. Petrol., 110, 329–45.Google Scholar