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Chemical zonation and relative timing of growth sections in garnets from eclogites of the Leaota Massif, South Carpathians

Published online by Cambridge University Press:  05 July 2018

G. Săbău ,
E. Negulescu  and
H.-J. Massonne
G. Săbău*
Affiliation:
Geological Institute of Romania, 1 Caransebeş st., RO-012271 Bucharest 32, Romania
E. Negulescu
Affiliation:
Geological Institute of Romania, 1 Caransebeş st., RO-012271 Bucharest 32, Romania
H.-J. Massonne
Affiliation:
Institut für Mineralogie und Kristallchemie, Azenbergstr. 18, D-70174 Stuttgart, Germany
*
*E-mail: [email protected]
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Abstract

We have investigated the chemical zoning of garnet in three texturally different eclogite types from the Leaota Massif, Romania, to test the various zonation patterns of Ca, Fe, Mg and Mn as indices of time-lines in porphyroblastic garnets. Mn zonation was found to mark various growth stages very well. It indicates in each of our three case studies a complex growth history dominated by multiple nucleation and coalescence, but also interrupted by partial resorption, as shown by morphological characteristics. Chemical variations of the main elements in garnet during prograde high-pressure metamorphism define time-lines other than those of Mn which decrease, highlighting the stages of porphyroblastic growth. In particular, the Ca/Mn, Mg/Mn and Mg/Fe ratios are useful in late growth stages, when low Mn contents and radial gradients do not allow a satisfactory resolution of Mn time-lines. These ratio-based time-lines further substantiate the potential of Mn time-lines in revealing non-concentric porphyroblastic growth. This is important in order to correctly relate garnet growth stages to stable mineral assemblages, a prerequisite for a reliable derivation of the metamorphic history of the host rock.

Keywords

garnetcrystal chemistrygrowth sectionseclogiteRomania
Type
Research Article
Information
Mineralogical Magazine , Volume 70 , Issue 6 , December 2006 , pp. 655 - 667
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2006

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References

Bernhardt, H.-J., Massonne, H.-J., Reinecke, T., Reinhardt, J. and Willner, A. (1995) Digital element distribution maps, an aid for petrological investigations. Berichte der Deutschen Mineralogischen Gesellschaft, Beihefte zum European Journal of Mineralogy, 7, No. 1, 28.Google Scholar
Costin, G. and Luffi, P. (2001) Cr-rich minerals in eclogites from Raul Targului (Iezer Mts., South Carpathians). Anuarul Institutului Geological României, 72, Supplement, 11–12.Google Scholar
Dobbs, H.T., Peruzzo, L., Seno, F., Spiess, R. and Prior, D.J. (2003) Unravelling the Schneeberg garnet puzzle: a numerical model of multiple nucleation and coalescence. Contributions to Mineralogy and Petrology, 146, 1–9.CrossRefGoogle Scholar
Hirsch, D.M., Prior, D.J. and Carlson, W.D. (2003) An overgrowth model to explain multiple, dispersed high-Mn regions in the cores of garnet porphyroblasts. American Mineralogist, 88, 131–141.CrossRefGoogle Scholar
Hollister, L.S. (1966) Garnet zoning: an interpretation based on the Rayleigh fractionation model. Science, 154, 1647–1651.CrossRefGoogle Scholar
Iancu, V., Mărunţiu, M., Johann, V. and Ledru, P. (1998) High-grade metamorphic rocks in the pre-Alpine nappe stack of the Getic-Supragetic basement (Median Dacides, South Carpathians, Romania). Mineralogy and Petrology, 63, 173–198.CrossRefGoogle Scholar
Kretz, R. (1983) Symbols for rock-forming minerals. American Mineralogist, 68, 277–279.Google Scholar
Mărunţiu, M., Johan, V., Iancu, V., Ledru, P. and Cocherie, A. (1997) Kyanite-bearing eclogite from the Leaota Mountains (South Carpathians, Romania): mineral associations and metamorphic evolution. Comptes Rendus de l'Academie de Sciénces Série II a: Sciences de la Terre et des Planétes, 325, 831–838.Google Scholar
Medaris, L.G. Jr., Ducea, M., Ghent, E. and Iancu, V. (2003) Conditions and timing of high-pressure Variscan metamorphism in the South Carpathians, Romania. Lithos, 70, 141–161.CrossRefGoogle Scholar
Mullen, E.D. (1983) MnO/TiO2/P2O5: a minor element discriminant for basaltic rocks of oceanic environments and its implications for petrogenesis. Earth and Planetary Science Letters, 62, 53–62.CrossRefGoogle Scholar
Săbău, G. (2000) A possible UHP-eclogite in the Leaota Mts. (South Carpathians) and its history from high-pressure melting to retrograde inclusion in a subduction melange. Lithos, 52, 253–276.CrossRefGoogle Scholar
Săbău, G. and Massonne, H.-J. (2003) Relationships among eclogite bodies and host rocks in the Lotru metamorphic suite (South Carpathians, Romania): Petrologieal evidence for multistage tectonic emplacement of eclogites in a medium pressure terrain. International Geology Review, 45, 225–262.CrossRefGoogle Scholar
Spear, F.S. and Daniel, C.G. (1998) Three-dimensional imaging of garnet porphyroblast sizes and chemical zoning: Nucleation and growth history in the garnet zone. Geological Materials Research, 1, no. 1, 44 pp.Google Scholar
Spiess, R., Peruzzo, L., Prior, D.J. and Wheeler, J. (2001) Development of garnet porphyroblasts by multiple nucleation, coalescence and boundary misorientation-driven rotations. Journal of Metamorphic Geology, 19, 269–290.Google Scholar
Spry, A. (1969) Metamorphic Textures. Pergamon Press, Oxford, UK, 350 pp.Google Scholar
Tracy, R.J. (1982) Compositional zoning and inclusions in metamorphic minerals. Pp. 355–397 in: Characterization of Metamorphism through Mineral Equilibria (Ferry, J.M., editor). Reviews in Mineralogy, 10, Mineralogical Society of America, Washington, D.C. Google Scholar
Wheeler, J. (1991) A view of texture dynamics. Terra Nova, 3, 123–136.CrossRefGoogle Scholar
Yang, P. and Rivers, T. (2001) Chromium and manganese zoning in pelitic garnet and kyanite: spiral, overprint and oscillatory (?) zoning patterns and the role of growth rate. Journal of Metamorphic Geology, 19, 455–476.CrossRefGoogle Scholar