Dioriticke horniny v moldanubickem (jihoceskem) batolitu

Besides the highly prevailing granites, the South Bohemian (Moldanubian) Batholith (SBB) comprises several satellite bodies of more mafie composition. Our research has been focused on petrographic and geochemical correlation of dioritic rocks frora Chlum and Třebonín-Velešín in S Bohemia with those occurring in Austria (Gebharts). These rocks correspond to hornblende-biotite diorite, quartz diorite and even tonalite; the K-feldspar bearing varieties are quartz monzonites to granodiorites. Durbachite has been found in a close spatial association to dioritic rocks within the Třebonín-Velešín massif. All the dioritic rocks under study are relatively rich in potassium and correspond with the high-K calc-alkaline to shoshonitic series. They share many compositional features with some redwitzites from W and SW marginal parts of the Bohemian Massif. Dioritic rocks of the Třebonín and Gebharts massifs are more potassic compared to the Chlum massif. A simple crystal fractionation model cannot explain the chemical variations and a role of enriched mantle sources combined with interaction of the mantle-derived magmas with material of the Continental crust are proposed. Some transitional rock varieties could originate by mixing of the ultrapotassic (durbachite) and K-rich calc-alkaline (dioritic) magmas. We believe that mantle-derived mafic magmas and their thermal input contributed to the origin of the SBB substantially.