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Petrology and geochemistry of plutonic rocks from the Polička and Zábřeh crystalline units (NE Bohemian Massif)

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Author(s): Buriánek D | Němečková M | Hanžl P

Journal: Bulletin of Geosciences
ISSN 1214-1119

Volume: 78;
Issue: 1;
Start page: 9;
Date: 2003;
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Keywords: Polička Crystalline Complex | Zábřeh Crystalline Complex | plutonic rocks | tonalite | whole-rock geochemistry | geobarometry | geothermometry

ABSTRACT
Polička and Zábřeh Crystalline Complexes are units situated in the NE part of the Bohemian Massif. They are composed of similar metamorphosed volcanosedimentary sequences intruded by numerous plutonic bodies of Variscan age. The mafic, tonalite and granite plutonic suites were distinguished here based on petrology and geochemistry. Rocks of the mafic suite show a primitive chemical composition and were metamorphosed under conditions of lower amphibolite facies. Rocks of the tonalite suite are metaluminous and their chemical composition in the two units is almost the same, but these rocks differ in the fO2 values. Contamination of magma by crustal rocks was confirmed by the data obtained from mineral chemistry. Submagmatic to solid-state deformation fabric in tonalites is concordant with the adjacent country rocks and points to syn-tectonic or early post-tectonic character of emplacement. Rocks of the tonalite suite were emplaced at different crustal levels in the Polička Crystalline Complex. In the southern part of the unit, crystallization of quartz gabbros occurred at pressures of 6 to 8 kbar, with temperature ranging within 659-785 °C. Conditions of 559-750 °C and 3-6 kbar dominated in other rock types of the tonalite suite. The PT conditions of tonalite intrusion in the Zábřeh Crystalline Complex are estimated at 706-795 °C and 3-4 kbar. These values correspond with those obtained from the adjacent metapelites. Granite suite is rather weakly represented, granites evolved from a mature source. A different magmatic pulse is the easiest way to explain quite different trends in variation diagrams compared to the spatially- and age-related tonalite suite.

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