Hostname: page-component-cd9895bd7-gbm5v Total loading time: 0 Render date: 2024-12-30T20:23:28.406Z Has data issue: false hasContentIssue false
  • English
  • Français

Influence of the mode and distribution of garnet and biotite on Grt-Bt thermometry: evidence from a single-sample case study

Published online by Cambridge University Press:  05 July 2018

J. V. Owen  and
J. D. Greenough
J. V. Owen
Affiliation:
Department of Geology, Saint Mary's University, Halifax, N.S., Canada B3H 3C3
J. D. Greenough
Affiliation:
Department of Geological Sciences, Okanagan College, 3333 College Way, Kelowna, B.C., Canada V1V 1V7
Get access Rights & Permissions [Opens in a new window]

Abstract

Detailed microprobe and modal data for a sample of layered, garnetiferous, quartzose paragneiss reveal significant differences in garnet-biotite Mg-Fe distribution coefficients (Kd) — and hence paleotemperatures — determined for leucocratic (modal Grt+Bt<25 vol.%) and mesocratic (Grt+Bt> 25 vol.%) layers. In leucocratic layers, lnKd determined from both the core and rim compositions of minerals shows a range of values that varies sympathetically with the absolute amount of garnet and biotite, and, as demonstrated in other studies, inversely with the distance separating both minerals. Due to the small size (<2 mm) of garnets, which facilitated diffusional re-equilibration during cooling from peak metamorphic temperature, lnKd does not correlate to modal Bt/Grt ratios. The largest garnets, which occur in mesocratic layers, nonetheless tend to preserve the most pronounced (retrograde) zoning patterns (i.e. rimward increase in Fe/Mg), consequently mineral core composition lnKd values correlate with grain diameter except where garnets contain abundant biotite inclusions. The highest Grt-Bt temperatures (∼700°C are recorded by: (1) the composition of relatively widely-separated (>0.3 mm) grains in highly leucocratic layers; and (2) the core compositions of relatively large (>1 mm), inclusion-free grains in mesocratic layers. More closely spaced garnets and biotites in leucocratic layers, and small grains in mesocratic layers, give a range of temperatures intermediate between Tmax and diffusional blocking temperatures (∼ 560°C) recorded by the rim compositions of contiguous grains.

Keywords

garnetbiotitethermometrypalaeotemperaturesparagneiss
Type
Mineralogy
Information
Mineralogical Magazine , Volume 59 , Issue 396 , September 1995 , pp. 497 - 504
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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.)

References

Berman, R.G. (1990) Mixing properties of Ca-Mg-Fe-Mn garnets. Amer. Mineral., 75, 328–44.Google Scholar
Berman, R.G. (1991) Thermobarometry using multi-equilibrium calculations: a new technique, with petrological applications. Canad. Mineral., 29, 833–55.Google Scholar
Berman, R.G. and Brown, T.H. (1988) A general method for thermobarometric calculations with a revised garnet solution model and geologic applications. Geol. Soc. Amer., Abstracts with Programs, 20, A98.Google Scholar
Brown, T.H., Berman, R.G. and Perkins, E.H. (1988) GEO-CALC Software package for calculation and display of pressure-temperature-composition phase diagrams using an IBM or compatible personal computer. Comp. and GeoscL, 14, 279–89.CrossRefGoogle Scholar
Droop, G.T.R. (1987) A general equation for estimating Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichio-metric criteria. Mineral. Mag., 51, 431–5.CrossRefGoogle Scholar
Emslie, R.F. and Stirling, J.A.R. (1993) Rapakivi and related granitoids of the Nain Plutonic Suite: geochemistry, mineral assemblages and fluid equilibria. Canad. Mineral., 31, 821–47.Google Scholar
Guidotti, C.V. and Dyar, M.D. (1991) Ferric iron in metamorphic biotite and its petrologic and crystal-lochemical implications. Amer. Mineral., 76, 161–75.Google Scholar
Indares, A. and Martignole, J. (1985a) Biotite—garnet geothermometry in the granulite facies: the influence of Ti and Al in biotite. Amer. Mineral., 70, 272–8.Google Scholar
Indares, A. and Martignole, J. (1985i>) Biotite—garnet geothermometry in granulite-facies rocks: evaluation of equilibrium criteria. Canad. Mineral., 23, 187–93.)+Biotite—garnet+geothermometry+in+granulite-facies+rocks:+evaluation+of+equilibrium+criteria.+Canad.+Mineral.,+23,+187–93.>Google Scholar
Lasaga, A.C., Richardson, S.M. and Holland, H.D. (1977) The mathematics of cation diffusion and exchange between silicate minerals during retro-grade metamorphism. In: Energetics of Geological Processes, (Saxena, S.K. and Bhattacharji, S., eds), Springer-Verlag, New York, pp. 354-87.Google Scholar
Martignole, J. and Pouget, P. (1993) Contrasting zoning profiles in high-grade garnets: evidence for the allochthonous nature of a Grenville province terrane. Earth Planet. Sci. Lett., 120, 177–85.CrossRefGoogle Scholar
McMullin, D.W.A., Berman, R.G. and Greenwood, H.J. (1991) Calibration of the SGAM thermobarometer for pelitic rocks using data from phase-equilibrium experiments and natural assemblages. Canad. Mineral, 29, 889–908.Google Scholar
Owen, J.V. (1992) Comparative petrology of gneissic rocks in southwestern Newfoundland. Canad. J. Earth Sci., 29, 2663–76.CrossRefGoogle Scholar
Perchuk, L.L. and Lavrent'eva, I.V. (1983) Experimental investigation of exchange equilibria in the system cordierite-garnet-biotite. In: Advances in Physical Geochemistry, (Saxena, S.K., ed.). Springer-Verlag, New York pp.1–60.Google Scholar
Robinson, P. (1991) The eye of the petrographer, the mind of the petrologist. Amer. Mineral., 76, 1781–810.Google Scholar
Selverstone, J. and Chamberlain, C.P. (1990) Apparent isobaric cooling paths from granulites: Two counterexamples from British Columbia and New Hampshire. Geology, 18, 307–10.2.3.CO;2>CrossRefGoogle Scholar
Spear, F.S. and Florence, F.P. (1992) Thermobarometry in granulites: pitfalls and new approaches. Precamb. Res., 55, 209–41.CrossRefGoogle Scholar
Spear, F.S. (1989) Petrologic determination of meta-morphic pressure-temperature-time paths. In: Metamorphic pressure-temperature-time paths. (Crawford, M.L. and Padovani, E., eds), Amer. Geophys. Union Short Course in Geology, 7, 1–55.Google Scholar
Tracy, R.J., Robinson, P. and Thompson, A.B. (1976) Garnet compositional zoning in the determination of temperature and pressure of metamorphism, central Massachusetts. Amer. Mineral., 61, 762–75.Google Scholar
Williams, M.L. and Grambling, J.A. (1990) Manganese, ferric iron, and the equilibrium between garnet and biotite. Amer. Mineral, 75, 886–908.Google Scholar