Calc-silicate rocks from Polička crystalline ComplexArticle PDF
Calc-silicate rocks from Polička crystalline Complex
Two distinct types of calc-silicate rock occur in the Polička Crystalline Complex. The biotite and two-mica gneisses with nodules calc-silicate rocks are typical members of a monotonous zone Polička Crystalline Complex. Elongated bodies of calc-silicate rock are situated in the varied zone along boundary between Polička Crystalline Complex and Svratka Crystalline Complex. They are associated with amphibolites, marbles and gneisses. The mineral assemblage is similar in both groups (nodules calc-silicate rocks: Qtz + Pl + Di + Ttn ± Czo ± Amp ± Grt ± Cal and bodies of calc-silicate rock: Qtz + Pl + Di + Ttn ± Kfs ± Scp ± Ep (Czo) ± Amp ± Grt ± Cal ± Chl). Mineral equilibria in calc-silicate rocks and surrounding metapelites provide estimates of metamorphic PT conditions for both groups 570–680 °C and 5–7 kbar. The garnet is typical constituent for nodules calc-silicate rocks on the major part Polička Crystalline Complex. However in the bodies of calc-silicate rock garnet is present only on the SE margin Polička Crystalline Complex. The spatial distribution of garnets depends on the chemical composition rocks and fluids during metamorphic evolution. Fluid compositions supposed for the nodules calc-silicate rocks are systematically lower in XCO2 than those from bodies of calc-silicate rock. Chemical and mineralogical work leads to the conclusion that they resulted from regional metamorphism under amphibolite facies conditions. The occurrence of actinolite, chlorite and clinozoisite resulted from later retrograde metamorphism.
David Buriánek, Czech Geological Survey, Leitnerova 22, 658 59, Brno, Czech Republic; email@example.com