Petrography of the Polička Crystalline ComplexArticle PDF
Petrography of the Polička Crystalline Complex
The Polička Crystalline Complex is a metamorphosed volcano-sedimentary complex situated in the E part of the Bohemian Massif. Lithotectonic sequences of the Polička Crystalline Complex can be subdivided on the three subunits.
The basal subunit is composed of medium-grained biotite and two-mica gneisses (±Grt ±Sil) with highly deformed bodies of metagranitoids, amphibolites, marbles, calc-silicate rocks and granulites. Granulites are tectonically incorporated in to Polička Crystalline Complex. Mineral assemblage of metapelites preserved post peak stage evolution granulites (620–680 °C and 6–8 kbars) accompanied with anatexis and intrusion dykes of granitoid.
The middle subunit of Polička Crystalline Complex consists of the monotonous complex of mediumgrained biotite to two-mica paragneisses (±Grt ±Sil) with locally abundant calc-silicate nodules up to 0.5 m thicks. Monotonous rocks complex is interpreted as metagreywackes with intercalations metapelites and rare metaconglomerates. The metapelites from middle subunit Polička Crystalline Complex indicates anticlockwise metamorphic evolution. Relics of the oldest LP–MT metamorphism (M1) are preserved mainly in the northernmost part unit. Somewhat later metamorphosis under P–T conditions 580–680 °C a 5–7 kbar affected major part Polička Crystalline Complex (M2). This metamorphic event is locally related with partial melting of metapelites. During exhumation are K-feldspar and sillimanite in the migmatites partially replaced by muscovite (M3).
The upper subunit is in the eastern part Polička Crystalline Complex, and consists of the mica schist with quartzite and paragneisses intercalations. The two-mica mica schist (±St ±Grt ±Sill ±Pl ±Ky) forms several strips NW–SE orientation along NE margin Polička Crystalline Complex and preserved P–T conditions 630–660 °C and 7–8 kbar.
Variscan magmatic rocks represent characteristic members of Polička Crystalline Complex. The basic, tonalite and granite plutonic suites were distinguished here on the basis of petrology and geochemistry. Basic and tonalite suite intruded predominantly middle subunit Polička Crystalline Complex. Dykes and bodies rocks of granite suite are widely distributed in all subunits Polička Crystalline Complex.
David Buriánek, Czech Geological Survey, Leitnerova 23, Brno, e-mail: email@example.com