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Mechanism of formation of atoll garnet during high-pressure metamorphism

Published online by Cambridge University Press:  05 July 2018

S. W. Faryad ,
H. Klápová  and
L. Nosál
S. W. Faryad*
Affiliation:
Institute of Petrology and Structural Geology, Charles University, Albertov 6, 128 43 Praha 2, Czech Republic
H. Klápová
Affiliation:
Institute of Petrology and Structural Geology, Charles University, Albertov 6, 128 43 Praha 2, Czech Republic
L. Nosál
Affiliation:
Institute of Petrology and Structural Geology, Charles University, Albertov 6, 128 43 Praha 2, Czech Republic
*
*E-mail: faryad@natur.cuni.cz
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Abstract

Atoll garnet has been found in metabasites and quartz- and mica-rich rocks that have experienced low- to medium-temperature, high-pressure eclogite facies metamorphism in the Krušné Hory (Erzgebirge). They occur in several localities but are restricted to thin, texturally distinct zones, even on a thin-section scale. The mechanism of atoll garnet formation is documented by a series of micrographs and compositional maps and profiles of atoll garnet in combination with textural relations to other phases in the rocks. The core of full garnet or its relics in the atoll garnet have larger Ca and Fe, but smaller Mg contents, compared with the thin rim (ring). In addition to quartz, Na-Ca amphibole and phengite, the atoll cores are filled by a new garnet that has a composition similar to the outer rim. Formation of the atoll garnet is interpreted as resulting from fluid infiltration and element exchange between the garnet core and matrix, a process facilitated by a temperature increase during eclogite facies metamorphism. In addition to fluid access, the primary textures, mainly grain size, were also effective for the atoll garnet formation. Small grain fractions with thin rims were easily infiltrated by fluid, which used the short distance for element exchange between core and matrix. The core garnet was gradually dissolved and replaced by new garnet having the same crystallographic orientation as the rim or relics in the core.

Keywords

atoll garneteclogitefluid infiltrationBohemian Massif
Type
Research Article
Information
Mineralogical Magazine , Volume 74 , Issue 1 , February 2010 , pp. 111 - 126
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

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References

Ai, Y. (1994) A revision of the garnet-clinopyroxene Fe2+-Mg exchange geothermometer. Contributions to Mineralogy and Petrology, 115, 467–473.CrossRefGoogle Scholar
Atherton, M.P. and Edmunds, W.M. (1966) An electron microprobe study of some zoned garnets from metamorphic rocks. Earth and Planetary Science Letters, 1, 185–193.CrossRefGoogle Scholar
Blum, A.E., Yund, R.A. and Lasaga, A.C. (1990) The effect of dislocation density on the dissolution rate of quartz. Geochimica et Cosmochimica Acta, 54, 283–297.CrossRefGoogle Scholar
Cheng, H., Nakamura, E., Kobayashi, K. and Zhou, Z. (2007) Origin of atoll garnets in eclogites and implications for the redistribution of trace elements during slab exhumation in a continental subduction zone. American Mineralogist, 92, 1119–1129.CrossRefGoogle Scholar
Christian, J.W. (1975) The Theory of Transformations in Metals and Alloys, Part 1: Equilibrium and General Kinetic Theory, 2nd Edition. Pergamon, Oxford, UK.Google Scholar
Cooper, A.F. (1972) Progressive metamorphism of metabasic rocks from the Haast Schist Group of southern New Zealand. Journal of Petrology, 13, 457–492.CrossRefGoogle Scholar
Dobbs, H.T., Peruzzo, L., Seno, F., Spiess, R. and Prior, D.J. (2003) Unraveling the Schneeberg garnet puzzle. A numerical model of multiple nucleation and coalescence. Contributions to Mineralogy and Petrology, 146, 1–9.CrossRefGoogle Scholar
Faryad, S.W. (2009) The Kutná Hora Complex (Moldanubian zone, Bohemian Massif): A composite of crustal and mantle rocks subducted to HP/UHP conditions. Lithos, 109, 193–208.CrossRefGoogle Scholar
Faryad, S.W., Perraki, M. and Vrána, S. (2006) P-T evolution and reaction textures in retrogressed eclogites from Svetlik, the Moldanubian Zone (Czech Republic). Mineralogy and Petrology, 88, 297–319.CrossRefGoogle Scholar
Florence, F.P. and Spear, F.S. (1991) Effects of diffusional modification of garnet growth zoning on P–T path calculations. Contributions to Mineralogy and Petrology, 107, 487–500.CrossRefGoogle Scholar
Franke, W. (2000) The mid-European segment of the Variscides: Tectonostratigraphic units, terrane boundaries, and plate tectonic evolution. Pp. 35–61 in: Orogenic Processes: Quantification and Modelling in the Variscan Belt. (Franke, W. Haak, V., Oncken, O. and Tanner, D., editors). Special Publications, 179, The Geological Society, London.Google Scholar
Green, J.F.N. (1915) The garnets and streaky rocks of the English Lake District. Mineralogical Magazine, 17, 207.CrossRefGoogle Scholar
Hames, W.E. and Menard, T. (1993) Fluid-assisted modification of garnet composition along rims, cracks and mineral inclusion boundaries in samples of amphibolite facies schists. American Mineralogist, 78, 338–344.Google Scholar
Hwang, S.L., Shen, P., Yui, T.F. and Chu, H.T. (2003) On the mechanism of resorption zoning in metamorphic garnet. Journal of Metamorphic Geology, 21, 761–769.CrossRefGoogle Scholar
Joesten, R. (1991) Grain–boundary diffusion kinetics in silicate and oxide minerals. Pp. 345–395 in: Diffusion, Atomic Ordering and Mass Transport (Ganguly, J., editor), Springer, Berlin.CrossRefGoogle Scholar
Klápová, H. (1990) Eclogites of the Bohemian part of the Saxothuringicum. Rozpravy Československé akademie věd, (řada matematických a přírodních věd), 100(5), 3–86. ISSN 0069-228X, Academia Praha.Google Scholar
Klápová, H., Konopásek, J. and Schulmann, K. (1998) Eclogites from the Czech part of the Erzgebirge: Multi-stage metamorphic, and structural evolution. Journal of the Geological Society, 155, 567–583.CrossRefGoogle Scholar
Konopásek, J., Schulmann, K. and Lexa, O. (2001) Structural evolution of the central part of the Krušné Hory (Erzgebirge) Mountains in the Czech Republic – evidence for changing stress regime during Variscan compression. Journal of Structural Geology, 23, 1373–1392.CrossRefGoogle Scholar
Konrad-Schmolke, M., O'Brien, P.J. and Heidelbach, F. (2007) Compositional re-equilibration of garnet: the importance of sub-grain boundaries. European Journal of Mineralogy, 19, 431–438.CrossRefGoogle Scholar
Korzhinskii, D.S. (1970) Theory of Metasomatic Zoning. Clarendon, Oxford. UK, 162 pp.Google Scholar
Massonne, H-J. and Kopp, J. (2005) A low-variance mineral assemblage with talc and phengite in an eclogite from the Saxonian Erzgebirge, Central Europe, and its P–T evolution. Journal of Petrology, 46, 355–375.CrossRefGoogle Scholar
Medaris, G., Jelínek, E. and Mísař, Z. (1995) Czech eclogites – terrane settings and implications for variscan tectonic evolution of the Bohemian Massif. European Journal of Mineralogy, 7, 7–28.CrossRefGoogle Scholar
Nakamura, D., Svojtka, M., Naemura, K. and Hirajima, T. (2004) Very-high-pressure (>4 GPa) eclogite associated with the Moldanubian Zone garnet peridotite (Nové Dvory, Czech Republic). Journal of Metamorphic Geology, 22, 593–603.CrossRefGoogle Scholar
O’Brien, P. 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. Geologische Rundschau, 84, 473–488.CrossRefGoogle Scholar
Okamoto, K. and Maruyama, S. (1999) The high-pressure stability limits of lawsonite in the MORB+H2O system. American Mineralogist, 84, 362–373.CrossRefGoogle Scholar
Rast, N. (1965) Nucleation and growth of metamorphic minerals. Pp. 73–102 in: Controls of Metamorphism (Pitcher, W.S. and Flinn, G.W., editors). Oliver and Boyd, Edinburgh.Google Scholar
Ravna, E.K. (2000) The garnet-clinopyroxene Fe2+-Mg geothermometer: an updated calibration. Journal of Metamorphic Geology, 18, 211–219.CrossRefGoogle Scholar
Săbău, G., Negulescu, E. and Massonne, H.-J. (2006) Chemical zonation and relative timing of growth sections in garnets from eclogites of the Leaota Massif, South Carpathians. Mineralogical Magazine, 70, 655–667.CrossRefGoogle Scholar
Smellie, J.A.T. (1974) Formation of atoll garnets from the aureole of the Ardara pluton, Co. Donegal, Ireland. Mineralogical Magazine, 39, 878–888.CrossRefGoogle Scholar
Spiess, R., Peruzzo, L., Prior, D.J. and Wheeler, J. (2001) Development of garnet porphyroblasts by multiple nucleation, coalescence and boundary driven rotations. Journal of Metamorphic Geology, 19, 269–290.Google Scholar
Spry, A. (1969) Metamorphic Textures. Pergamon Press, Oxford, UK, 350 pp.Google Scholar
Thompson, J.B. (1959) Local equilibrium in metasomatic processes. Pp. 340–361 in: Researches in Geochemistry I (Abelson, P.H., editor). Wiley, New York.Google Scholar
Waters, D.J. (2001) The significance of prograde and retrograde quartz-bearing intergrowth microstructures in partially melted granulite-facies rocks. Lithos, 56, 97–110.CrossRefGoogle Scholar
Whitney, D.L. (1991) Calcium depletion halos and Fe-Mn-Mg zoning around faceted plagioclase inclusions in garnet from a high-grade pelitic gneiss. American Mineralogist, 76. 493–501.Google Scholar
Whitney, D.L., Mechum, T.A., Dilek, Y. and Kuehner, S.M. (1996) Modification of garnet by fluid infiltration during regional metamorphism in garnet through sillimanite-zone rocks, Dutchess County, New York. American Mineralogist, 81, 96–705.CrossRefGoogle Scholar