Microstructural and mineralogical evidence for limited involvement of magma mixing in the petrogenesis of a Hercynian high-K calc-alkaline intrusion:the Kozarovice granodiorite, Central Bohemian Pluton, Czech Republic

Textural and mineralogical features in the high-K calc-alkaline Kozarovice granodiorite (Hercynian Central Bohemian Pluton, Bohemian Massif) and assoc iated small quartz monzonite masses imply that mixing between acid (granodi oritic) and basic (monzonitic/monzogabbroic) magmas was locally petrogeneti cally significant. Net veining, with acicular apatite and numerous lath-shaped plagioclase cry stals present in the quartz monzonite, and abundant mafic microgranular enc laves (MME) in the granodiorite, indicate that as the monzonitic magma was injected into the granodioritic magma chamber, it rapidly cooled and was pa rtly disintegrated by the melt already present. Evidence from cathodolumine scence suggests that the two magmas exchanged early-formed plagioclase crys tals. In the quartz monzonite, granodiorite-derived crystals were overgrown by narrow calcic zones, followed by broad, normally zoned sodic rims. In t he granodiorite, plagioclase crystals with calcic cores overgrown by normal ly zoned sodic rims are interpreted as xenocrysts from the monzonite. After thermal adjustment, crystallisation of the monzonitic magma ceased relativ ely slowly, forming quartz and K-feldspar oikocrysts. Although the whale-rock geochemistry of the quartz monzonite and the MME su pport magma mixing, major- and trace-element based modelling of the host gr anodiorite has previously indicated an origin dominated by assimilation and fractional crystallisation. Magma mixing therefore seems to represent a lo cal modifying influence rather than the primary petrogenetic process.