Acta Musei Moraviae

Petrology and geochemistry of metadolerite from Jindřichov (Bruntál district)

This paper presents new information about petrology and geochemistry of metadolerite from Jindřichov (Bruntál district) which represents coarse to medium grained rock with ophitic to poikiloophitic texture composed mainly of albitised plagioclase, relict pyroxene (augite), opaque minerals (pseudomorphs after Ti-magnetite, ilmenite) and secondary minerals (chlorite, epidote, amphibole). Chemical composition of the rock was affected by hydrothermal alteration and / or regional metamorphosis which results to SiO₂ depletion and redistribution of alkalies and some LILEs. Primary character of rock is possible to reconstruct using immobile trace elements (Nb, Y, Zr, REE, etc.) and TiO₂, P₂O₅: metadolerite exhibits tholeitic character with clear within-plate affinity. Major mineralogical control of differenciation of parental magma play Fe-Ti oxide, plagiclase and apatite. The occurence of metadolerite from Jindřichov can be correlated with metabasites from Pokrzywna in Poland (aprox. 4.5 km from Jindřichov) and with rocks of Šternberk – Horní Benešov Belt. In comparison with metabasites from the southern part of Šternberk – Horní Benešov Belt, studied rock exhibits less enriched character and is, in contradiction to southern part of Šternberk – Horní Benešov Belt, subalcaline, which is probably in relation to different basement structure. The comparison with basic igneous rocks of Vrbno Group is difficult, but the major element chemistry of the rock is close to metabasites of second volcanic cycle in the Zlaté Hory ore district.