Ultrabazické Horniny Těšínitové Asociace v Západní Části Slezské Jednotky

Abstract

The teschenite association occurring in southwest part of the Silesian Unit (Carpathian Flysch Belt) consists of several types of predominantly alkaline basic to ultrabasic intrusive and extrusive igneous rocks. Ultrabasic rocks such as peridotites and picrites represent geochemically relatively primitive melt. Primary magmatic mineral assemblages of ultrabasic rocks are characterized by a large amount of olivine (Fo 81–86 mol. %), clinopyroxene (predominantly diopside: XMg = 0.65–0.85, Na = 0.02–0.04 apfu; aegirine-augite sometimes forms small rims around diopside: XMg = 0.00–0.14, Na = 0.40–0.98 apfu) and rare chrome spinel to chromite with Cr/(Cr+Al) values 0.55–0.62 in peridotite or 0.26–0.69 in picrites. Olivine, linopyroxenes or spinelides in these rocks appear as suitable for calculation of PT conditions. The temperatures obtained using the olivine-clinopyroxene thermobarometry (1 294–1 322 °C; 8–11 kbar) are consistent with the appearance of these two minerals in the crystallization sequence of peridotite. However, the temperatures calculated for spinelide inclusions in olivine are ~ 500 °C lower than the experimentally derived liquidus for ultrabasic melt. This difference can be explained by subsolidus re-equilibration during cooling. Younger mineral assemblage in peridotite consists of phlogopite, pargasite, and magnetite.