Potassic syenite from Shipka, Central Balkan Mts, Bulgaria: characterization and insight into the source

Petrographic, mineralogical and whole-rock chemistry data from a new outcrop of peralkaline potassic syenite of presumed Variscan age near the town of Shipka, are presented here. The syenites exhibit peralkaline chemistry and very potassic character which markedly differs from nearby situated potassic monzonites, known as Shipka pluton. In spite of the close spatial association of these two bodies, genetic link between them can hardly be supposed. The syenites are composed of K-feldspar, diopside, mica and late interstitial amphibole. Mineral composition reflects the agpaitic conditions of crystallization with formation of sodic amphibole and K-feldspars with important Sr and Ba contents. These rocks have peralkaline wholerock chemistry, very high potassic content and extreme enrichment in LILE, LREE, Th and U. Their trace element signature and isotope characteristics are in favour of derivation from metasomaticaly enriched mantle source.