Abstract

Ultrapotassic plutons from several domains of the Variscan orogenic belt have been in turn interpreted as syn- to post-orogenic due to their age spread, but assessment of their geodynamic setting and source regions is still open to interpretation. In the Svoge region (Bulgaria), at the southern margin of the Balkan orogen, peralkalic plutons are hosted within Ordovician pelites. The main intrusion, with lamproitic affinity, which hosts monzodiorite xenoliths and a polyphase syenite suite, was emplaced at a shallow level. 40Ar–39Ar dating by step-heating of amphibole and biotite yielded a Early Carboniferous intrusion age for the main body (337 ± 4 and 339.1 ± 1.6 Ma). The lamproite intrusion is silica-rich compared with bona fide lamproites and characterized by moderate LILE and LaN/YbN enrichments. Sr and Nd isotopic data (initial ϵNd in the range −4.87 to −5.88) suggest an origin in a depleted lithospheric mantle, possibly refertilized by eo-Variscan subduction. The high-K syn-tectonic plutonism in several zones of the Variscan orogen (Bohemian, Austro-Alpine, Vosges, French and Corsica domains) is consistent with a derivation of high-K magmatism from partial melting of metasomatized mantle following the subduction along the collision front between Gondwana and Laurasia.

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