Acta Musei Moraviae

Rocks of teschenite association in the surroundings of Valašské Meziříčí

The teschenite association occurring in southwest part the Silesian Unit of the flysh belt, the West Carpathians, consists of intrusive and extrusive igneous rocks with variable textures, structures and mineral abundances. These rocks comprise mainly basalt, monchiquite, fourchite, picrite, and teschenite. The results of the petrographical investigations provide evidence on their polyphase magmatic and postmagmatic evolution. Content Si, Al, Fe, K and Na grow in the melt during magmatic stages. The compositional evolution trend of pyroxene from Al-Ti diopside towards aegirine-augite and spinelides from chromium spinels core to magnetite rim can be explained due to crystallization of the residual melt under higher oxygen fugacity. The plenty of the observed textural and mineralogical features originated during injection of magma into wet sediments or extrusion on the sea floor and subsequent reaction with seawater. Alternation of pillow lavas, hyaloclastites, volcanoclastic rocks, sandstones and claystones was probably deposited in the bathyal zone, based on micropalaeontological and vulcanological evidence. During postmagmatic stage a part of the primary magmatic assemblage was transformed to the secondary minerals. Alteration products include chlorite, magnetite, serpentine, limonite, albite, titanite, K-fedspar and calcite, some of which fill vesicles and/or joints.