Hostname: page-component-848d4c4894-nr4z6 Total loading time: 0 Render date: 2024-06-05T17:53:11.725Z Has data issue: false hasContentIssue false
  • English
  • Français

Asymmetric zoning profiles in garnet from HP-HT granulite and implications for volume and grain-boundary diffusion

Published online by Cambridge University Press:  05 July 2018

P. J. O’Brien
P. J. O’Brien*
Affiliation:
Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany
Get access Rights & Permissions [Opens in a new window]

Abstract

Detailed electron-microprobe line profiles and small-area compositional maps of zoned garnets in a sample of high-pressure-high-temperature granulite show features inconsistent with commonly applied diffusion models. Larger grains of an early garnet generation have their highest Ca contents in domains away from the rim or inclusions but show a sharp fall in Ca balanced by increased Mg and Fe (and slightly higher XMg) towards inclusions and the rim. In domains with secondary biotite, the sharp decrease in Ca is accompanied by variations in XMg dependent upon proximity to biotite, thus producing one-sided, asymmetric profiles with XMg lower against biotite. As a consequence, rim compositions of the same grain are different on the sides adjacent and away from biotite and there is no relationship between grain size and rim XMg. Such a zoning pattern requires that grain-boundary diffusion is as slow as volume diffusion and implies the absence of a diffusion-enhancing grain-boundary fluid phase during the majority of the rock's high-temperature exhumation history. Diffusion models ignoring this probability could yield either cooling rates that were too fast, or extrapolated ages based on closure temperature models that were too old.

A second garnet generation in the same rock, grown in a Ca-rich domain resulting from kyanite breakdown, has irregularly distributed patches, identified by compositional mapping, containing higher Ca than the first-formed garnet but at lower XMg. Use of such garnet compositions for geothermobarometrical determination of the high-pressure granulite stage would clearly lead to erroneous results. The presence of such contrasting garnet compositions in a granulite-facies rock is clearly evidence of disequilibrium, and further supports the proposition that there was a lack of an effective transport medium even at the mm scale.

Keywords

garnetzoningdiffusiongranulite
Type
Research Article
Information
Mineralogical Magazine , Volume 63 , Issue 2 , April 1999 , pp. 227 - 238
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999 

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

Aftalion, M., Bowes, D.R. and Vrána, S. (1989) Early Carboniferous U-Pb zircon age for garnetiferous perpotassic granulites, Blanský les massif, Czechoslovakia. Neues Jahrb. Mineral., Mh.,145–52.Google Scholar
Becker, H. (1997) Sm-Nd garnet ages and cooling history of high-temperature garnet peridotite massifs and high-pressure granulites from lower Austria. Contrib. Mineral. Petrol., 127, 224–36.Google Scholar
Becker, H. and Altherr, R. (1991) Al-rich sapphirine in a high-P charnockite: reaction textures and P-T-evolution. Terra abstracts, 3, 437.Google Scholar
Bégin, N.J. and Pattison, D.R.M. (1994) Metamorphic evolution of granulites in the Minto Block, northern Québec: extraction of peak P-Tconditions taking account of late Fe-Mg exchange. J. Metam. Geol., 12,411–28.10.1111/j.1525-1314.1994.tb00032.xGoogle Scholar
Behr, H.-J. (1978). Subfluenz-Prozesse im Grundgebirgs-Stockwerk Mitteleuropas. Z. dt. geol. Ges., 129,283–318.Google Scholar
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
Brenker, F.E. and Brey, G.P. (1997) Reconstruction of the exhumation path of the Alpe Arami garnet-peridotite body from depths exceeding 160 km. J. Metam. Geol., 15, 581–92.10.1111/j.1525-1314.1997.tb00637.xGoogle Scholar
Burton, K.W. and O’Nions, R.K. (1991) Highresolution garnet chronometry and the rates of metamorphic processes. Earth Planet. Sci. Lett., 107, 649–71.10.1016/0012-821X(91)90109-UGoogle Scholar
Carswell, D.A. and O’Brien, P.J. (1993) Thermobarometry and geotectonic significance of high pressure granulites: examples from the Moldanubian Zone of the Bohemian Massif in Lower Austria. J. Petrol., 34, 427–59.Google Scholar
Carswell, D.A., Möller, C. and O’Brien, P.J. (1989) Origin of sapphirine symplectites in metabasites from Mitterbachgraben, Dunkelsteinerwald granulite complex, Lower Austria. Eur. J. Mineral., 1, 455–66.10.1127/ejm/1/3/0455Google Scholar
Chakraborty, S. and Ganguly, J. (1990) Compositional zoning and cation diffusion in aluminosilicate garnets. In Diffusion, atomic ordering and mass transfer. (Ganguly, J., ed.), Advances in Physical Geochemistry Vol 8. Springer, New York, pp. 120–75.10.1007/978-1-4613-9019-0_4Google Scholar
Chakraborty, S. and Ganguly, J. (1992) Cation diffusion in aluminosilicate garnets: experimental determination in spessartine-almandine diffusion couples, evaluation of effective binary diffusion coefficients, and applications. Contrib. Mineral Petrol., 111, 74–86.10.1007/BF00296579Google Scholar
Dodson, M.H. (1973) Closure temperature in cooling geochronological and petrological systems. Contrib. Mineral. Petrol., 40, 259–74.10.1007/BF00373790Google Scholar
Dodson, M.H. (1986) Closure profiles in cooling systems. Materials Sci. Forum, 7, 145–54.10.4028/www.scientific.net/MSF.7.145Google Scholar
Duchêne, S., Albarède, F. and Lardeaux, J.-M. (1998) Mineral zoning and exhumation history in the Münchberg eclogites (Bohemia). Amer. J. Sci., 298, 30–59.10.2475/ajs.298.1.30Google Scholar
Ehlers, K. and Powell, R. (1994) An empirical modification of Dodson’s equation for closure temperature in binary systems. Geochim. Cosmochim. Acta, 58, 241–8.10.1016/0016-7037(94)90461-8Google Scholar
Ferry, J.M. and Spear, F.S. (1978) Experimental calibration of the partitioning of Fe and Mg between biotite and garnet. Contrib. Mineral. Petrol., 66, 113–7.Google Scholar
Fiala, J. (1995) General characteristics of the Moldanubian Zone. In Pre-Permian geology of Central and Eastern Europe, (Dallmeyer, R.D., Franke, W. and Weber, K., eds.), Springer, pp.417–8.10.1007/978-3-642-77518-5_42Google Scholar
Fiala, J., Matějovská, O. and Vaňková, V.B. (1987). Moldanubian granulites: source material and petro-genetic considerations. Neues Jahrb. Mineral Abh., 157, 133–65.Google Scholar
Florence, F.P. and Spear, F.S. (1995) Intergranular diffusion kinetics of Fe and Mg during retrograde metamorphism of a pelitic gneiss from the Adirondack Mountains. Earth Planet. Sci. Lett., 134, 329–40.10.1016/0012-821X(95)00129-ZGoogle Scholar
Fuchs, G. (1971) Zur Tektonik des östlichen Waldviertels (N. Ö.). Verh. Geol. B-A., Wien, 3, 424–40.Google Scholar
Fuchs, G. (1991) Das Bild der Böhmischen Masse im Umbruch. Jahrb. Geol. B-A., Wien 34, 701–10.Google Scholar
Fuchs, G. (1995) The Austrian part of the Moldanubicum. In Pre-Permian geology of Central and Eastern Europe,(Dallmeyer, R.D.,Franke, W. and Weber, K., eds.), Springer, pp. 422–6.Google Scholar
Fuhrmann, M.L. and Lindsley, D.H. (1988) Ternary-feldspar modelling and thermometry. Amer. Mineral., 73, 201–15.Google Scholar
Jenkin, G.R.T., Farrow, C.M., Falliek, A.E. and Higgins, D. (1994) Oxygen isotope exchange and closure temperatures in cooling rocks. J. Metam. Geol., 12, 221–36.10.1111/j.1525-1314.1994.tb00018.xGoogle Scholar
Jiang, J. and Lasaga, A.C. (1990) The effect of post-growth thermal events on growth-zoned garnet: implications for metamorphic P-T history calculations. Contrib. Mineral. Petrol., 105, 454–9.10.1007/BF00286832Google Scholar
Joesten, R. (1990) Grain boundary diffusion kinetics in silicate and oxide minerals. In Diffusion, atomic ordering and mass transfer,(Ganguly, J., ed.), Advances in Physical Geochemistry Vol 8, Springer, New York, pp. 345–95.10.1007/978-1-4613-9019-0_11Google Scholar
Kotková, J., Kröner, A., Todt, W. and Fiala, J. (1996) Zircon dating of North Bohemian granulites, Czech Republic: further evidence for the Lower Carboniferous high-pressure event in the Bohemian Massif. Geol. Rundsch., 85, 154–61.Google Scholar
Kotková;, J. and Harley, S.L. (1997) Mineral controls on the trace element and REE geochemistry of high-pressure leucogranulites from the Bohemian Massif. J. Czeeh. Geol. Soc., 42, 40.Google Scholar
Koziol, A.M. and Newton, R.C. (1989) Grossular activity-composition relationships in ternary garnets determined by reversed displaced-equilibrium experiments. Contrib. Mineral. Petrol., 103, 423–33.10.1007/BF01041750Google Scholar
Kröner, A., Jaekel, P., Reischmann, T. and Kroner, U. (1998) Further evidence for an early Carboniferous (∼340 Ma) age of high-grade metamorphism in the Saxonian granulite complex. Geol. Rundsch., 86, 751–66.10.1007/PL00009939Google Scholar
Kröner, A. and Willner, A.P. (1995) Magmatische und metamorphe Zirkonalter für Quarz-Feldspat-Gesteine der Gneis-Eklogit-Einheit des Erzgebirges. Terra Nostra, 95/8, 112.Google Scholar
Kryza, R., Pin, C. and Vielzeuf, D. (1996) High pressure granulites from the Sudetes (SW Poland) evidence of crustal subduction and collisional thickening in the variscan Belt. J. Metam. Geol., 14, 531–46.Google Scholar
Lasaga, A.C. (1983) Geospeedometry: an extension of geothermobarometry. In Kineties and equilibrium in mineral reactions,(Saxena, S.K., ed.), Advances in Physical Geochemistry Vol 3, Springer, pp. 81–114.10.1007/978-1-4612-5587-1_3Google Scholar
Lasaga, A.C., Richardson, S.M. and Holland, H.D. (1977) The mathematics of cation diffusion and exchange between silicate minerals during retrograde metamorphism. In Energetics of Geodynamic Process,(Saxena, S.K. and Bhattacharji, S.D., eds.), Springer, New York, pp. 353–88.10.1007/978-3-642-86574-9_15Google Scholar
Loomis, T.P., Ganguly, J. and Elphick, S.C. (1985) Experimental determination of cation diffusivifies in aluminosilicate garnets II. Multi-component simulation and tracer diffusion coefficients. Contrib. Mineral. Petrol., 90, 45–51.10.1007/BF00373040Google Scholar
Medaris, L.G. Jr. and Carswell, D.A. (1990) Petrogenesis of Mg-Cr garnet peridotites in European Metamorphic belts. In Eclogite Facies Rocks, (Carswell, D.A., ed.), Blackie, Glasgow, pp. 260–90.Google Scholar
Medaris, L.G. Jr., Beard, B.L., Johnson, C.M., Valley, J.W., Spicuzza, M.J., Jelínek, E. and Misaø, Z. (1995) Garnet pyroxenite and eclogite in the Bohemian Massif: geochemical evidence for Variscan recycling of subducted lithosphere. Geol. Rundsch., 84, 489–505.Google Scholar
Neumann, W. (1984) Zur erdgeschichtlichen Entwicklung des sächsischen Granulitmassivs. Z. angew. Geol, 30, 183–90.Google Scholar
O’Brien, P.J. (1997) Granulite facies overprints of eclogites: short-lived events deduced from diffusion modelling. In Precambrian Geology and Metamorphic Petrology,(Qian, X, You, Z and Halls, H.C., eds.), Proceedings of the 30th International Geological Congress, vol 17, VSP, Utrecht, Netherlands, pp. 157–71.Google Scholar
O’Brien, P.J. and Vrána, S. (1995) Eclogites with a short-lived granulite facies overprint in the Moldanubian Zone, Czech Republic: petrology, geochemistry and diffusion modelling of garnet zoning. Geol. Rundsch., 84, 473–88.Google Scholar
O’Brien, P.J. and Vrána, S. (1997) The eclogites in the Monotonous Series of the Moldanubian Zone and the theory of thermal pulses: a reply. Geol. Rundsch., 86, 716–9.Google Scholar
O’Brien, P.J., Kröner, A., Jaekel, P., Hegner, E., Zelaźniewicz, A. and Kryza, R. (1997). Petrological and isotopic studies on Palaeozoic high pressure granulites with a medium pressure overprint, Góry Sowie (Owl) Mts., Polish Sudetes. J. Petrol., 38, 433–56.Google Scholar
Owen, J.V. and Dostal, J. (1996) Contrasting corona structures in mafic granulite from the Blansky les complex, Bohemian Massif, Czech Republic. Canad. Mineral., 34, 959–66.Google Scholar
Petrakakis, K. and Jawecki, C. (1995) High-grade metamorphism and retrogression of Moldanubian granulites, Austria. Eur. J. Mineral. 7, 1183–203.10.1127/ejm/7/5/1183Google Scholar
Pin, C. and Vielzeuf, D. (1983) Granulites and related rocks in Variscan median Europe: a dualistic interpretation. Tectonophysics, 93, 47–74.10.1016/0040-1951(83)90233-0Google Scholar
Quadt, A. von (1993) The Saxonian Granulite Massif: new aspects from geochronological studies. Geol. Rundsch., 82, 516–30.10.1007/BF00212414Google Scholar
Schenk, V. and Todt, W. (1983) U-Pb Datierungen an Zirkon und Monazit der Granulite im Moldanubikum Niederösterreichs (Waldviertel). Fortschr. Mineral., 61, 190–1.Google Scholar
van Breemen, O., Aftalion, M., Bowes, D.R., Dudek, A., Misař, Z.,Povondra, P. and Vrána, S. (1982) Geochronological studies of the Bohemian Massif, Czechoslovakia, and their significance in the evolution of Central Europe. Trans. R. Soc. Edinburgh: Earth Sci., 73, 89–108.Google Scholar
Vrána, S. (1989) Perpotassic granulites from southern Bohemia. A new rock-type derived from partial melting of crustal rocks under upper mantle conditions, Contrib. Mineral. Petrol., 103, 510–22.10.1007/BF01041756Google Scholar
Vrána, S. and Jakeš, P. (1982) Orthopyroxene and two-pyroxene granulites from a segment of charnockitic crust in southern Bohemia. Bull. Geol. Surv. Prague, 57, 129–43.Google Scholar
Wendt, J.l., Kröner, A., Fiala, J. and Todt, W. (1994) U-Pb zircon and Sm-Nd dating of Moldanubian HP/HT granulites from South Bohemia, Czech Republic. J. Geol. Soc. Lond., 151, 83–90.10.1144/gsjgs.151.1.0083Google Scholar
Willner, A.P., Rötzler, K. and Maresch, W. (1997) Pressure-temperature and fluid evolution of quartzo-feldspathic metamorphic rocks with a relic high-pressure, granulite-facies history from the Central Erzgebirge (Saxony, Germany). J. Petrol., 38, 307–36.10.1093/petroj/38.3.307Google Scholar
Yardley, B.W.D. and Valley, J.W. (1997) The petrologic case for a dry lower crust. J. Geophys. Res., 102, 12173–85.10.1029/97JB00508Google Scholar