Mafické enklávy z granitoidů vystupujících v širším okolí Blanska

Vol.13,(2006)

Abstract
Mafic microgranular enclaves (MME) and associated host rocks occuring in the east granodiorite part of the Brno massif were studied petrologically and geochemically to establish their origin and to investigate the processes involved in their differentiation. Scarce enclaves display preserve narrow chilled margins. Many of enclaves show obvious similarities to their associated host rocks: they contain the identical mineral phases as their host rock, nevertheless the content of mafic minerals (biotite and hornblende) and opaque minerals is somewhat higher. Both types of rocks show some similar geochemical trends. Zoned plagioclase megacrysts in some enclaves contain anhedral cores jacketed by euhedral rim. These plagioclases could represent xenocrysts of early crystallised host rock phases mechanically accreted inward the liquid of enclaves. Acicular crystals of apatite and tiny lathy plagioclase in matrix are indicative of rapid crystallization of the enclaves liquid. Host rocks display intermediate to acid composition, while the enclaves are more basic. Macroscopic, microscopic and geochemical features indicate that the MME are products of mingling and incompletely mixing between a basic end member and host rocks of more acid composition.

Keywords:
granitoids; enclaves; petrology; geochemistry; xenocryst
References

Akal, C. – Helvaci, C. (1999): Mafic microgranular enclaves in the Kozak Granodiorite, western Anatolia. – Tr. J. of Earth Sciences, 8, 1-7. Ankara.
Barbarin, B. – Didier, J. (1991a): Macroscopic features of mafic microgranular enclaves. – In: Didier, J. – Barbarin, B. (eds.): Enclaves and Granite Petrology, 253-262, Elsevier. Amsterdam.
Barbarin, B. – Didier, J. (1991b): Review of the main hypotheses proposed for the genesis and evolution of mafic microgranular enclaves. ,– In Didier J. & Barbarin B. (eds.): Enclaves and Granite Petrology, 367-374, Elsevier. Amsterdam.
Bremen van O. – Aftalion, M. – Bowes, D.R. – Dudek, A. – Mísař, Z. – Povondra, P. – Vrána., S. (1982): Geochronological studies of the Bohemian Massif, Czechoslovakia, and their significance in the evolution of Central Europe. – Trans. Roy. Soc. Edinburgh: Earth Science, 73, 89-108. Edinburgh.
Dallmeyer et. al. (1994): Ar/Ar mineral age controls on the tectonic evolution of the southeastern Bohemian Massif. – Pre-Alpine crust in Austria, Excursion Guide.
Debon, F. (1991): Comparative major element chemistry in various „ microgranular enclave – plutonic host“ pairs. – In: Didier, J. – Barbarin, B. (eds.): Enclaves and Granite Petrology, 293-312, Elsevier. Amsterdam.
Didier, J. – Barbarin, B. eds. (1991): Enclaves and Granite Petrology. – 625 pp, Elsevier. Amsterdam.
Finger, F. – Pin, C. (1997): Arc-type crustal zoning in the Bruno-Vistulicum, Eastern Czech Republic; a trace of the late-Proterozoic Euro-Gondwana margin. – J. Czech Geol. Soc. 42, 53. Praha.
Gregerová, M. (1992): Petrochemie a klasifikace granitoidních hornin brněnské jednotky. – MS, kandid. práce, 1-243, Přírodověd. Fak. Masaryk. Univ. Brno.
Hanžl, P. (1996): Geologický profil brněnským masívem mezi Čebínem a Skalním Mlýnem. – MS, disert.práce, 1-75, Přírodov. Fak. Masaryk. Univ. Brno.
Hanžl, P. – Melichar, R. (1997): The Brno Massif: a Section through the Active Continental Margin or Composed Terrane? – Krystalinikum: Moravské zemské muzeum, 23, 33-58. Brno.
Hraško, L. – Kotov, A. B. – Salnikova, E. B. – Kovach, V. P. (1998): Enclaves in the Rochovce granite intrusion as indicators of the temperature and origin of the magma. – Geologica Carpathica, 49, 2, 125-138. Bratislava.
Erban, V. – Janousek, V. – Farrow, C. M. – Smid, J. (2003): Geochemical Data Toolkit (GCDkit): a key for magmatic geochemists to thetreasury of data analysis, statistics and graphics in R. Geolines, 16 , 25-6.
Sun, S. S. – McDonough, W. F. (1989): Chemical and isotopic systematic of oceanic basalts: implication for mantle composition and processes. In: Saunders A. D., Norry M. J. (Eds.), Magmatism in the Ocean Basins. Geological Society of London Special Publications, Leicester. 313-345.
Štelcl, J. – Schmidt, J. (1966): Zpráva o petrografickém výzkumu brněnského masívu. – Zpr. geol. Výzk. v r. 1964, 47-49. Praha.
Štelcl, J. – Weiss J. et al. (1986): Brněnský masív. – 1-255. UJEP Brno.
Vernon, R. H. (1983): Restite, xenoliths and microgranitoid enclaves in granites. – Journal and Proceedings of the Royal Society of New South Wales (Australia), 116, 77-103.
Vernon, R. H. (1991): Interpretation of microstructures of microgranitoid enclaves. – In Didier J. & Barbarin B. (eds.): Enclaves and Granite Petrology, 277-291, Elsevier. Amsterdam.
Wyllie, P. J. – Cox, K. G. – Biggar, G. M. (1962): The habit of apatite in synthetic systems and igneous rocks. J. Petrol., 3, 238 -243. 238-243.

Metrics

328

Views

142

PDF (Čeština) views