Acta Musei Moraviae

Mineralogy of ocellar quartz monzodiorites of the Žulová Pluton

Two main rock types can be distinguished in the Variscan Žulová Pluton at the NE margin of the Bohemian Massif: 1) biotite granites (dominate), and 2) biotite or amphibole-biotite granodiorites. Small dioritoide and gabbroide bodies occur along the margin of the pluton. The aim of the paper is petrographical and mineralogical description of quartz monzodiorite with a macroscopically well-developed ocellar texture from four localities at the SE margin of the Žulová Pluton. Quartz monzodiorite with titanite-centered light ocelli consist of plagioclase, K-feldspar, quartz, biotite and amphibole as major phases. Leucocratic ocelli essentially contain feldspars and quartz, minor biotite and amphibole is present. Anhedral titanite crystal always occurs at the core of the ocellus. The compositions of plagioclase, biotite and amphibole occurring in the ocelli and in the matrix outside the ocelli are identical in terms of major element values. The plagioclase compositions plot in the field of oligoclase and andesine (An_24–46). Biotite can be classified as annite. Amphiboles correspond from ferrohornblende to ferrohornblende/magnesiohornblende. Minor accessory minerals include apatite, ilmenite, allanite-(Ce), and zircon, as well as pyrrhotite and molybde – nite. Alteration minerals include clay minerals, white mica (sericite), chlorite (clinochlore), and epidote. The studied rocks can be regarded as typical hybrid rocks. Generally, the titanite-centered ocellar texture is a rarely observed texture from magma mixing and mingling zones (e.g., GOGOI et al. 2017).