High-Mg potassic rocks in the Balkan segment of the Variscan belt (Bulgaria): implications for the genesis of orogenic lamproite magmas

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/YbNenrichments. Sr and Nd isotopic data (initial ϵNdin 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.

Durbachites–Vaugnerites – a geodynamic marker in the central European Variscan orogen

“…Syenitic–monzodioritic rocks from the Svoge region (Cortesogno et al ., ) with an age of 337–338 Ma were recently described by Buzzi et al . (). These rocks have strong similarities to the durbachite–vaugnerite rocks of central Europe.…”

Mineralogical and geochemical characteristics of the Sedemte Prestola potassic alkaline pluton

“…Late Paleozoic tectonomagmatic activity resulted in the formation of alkaline intrusions with potassic affinity, which are typical for the central and eastern parts of the Variscan orogenic edifice (Dimitrov, 1935(Dimitrov, , 1937Kostov, 1950;Holub et al, 1997;Janousek and Gerdes, 2003;Dyulgerov, 2005;Kotkova et al, 2010;Krmíček et al, 2016;Buzzi et al 2010;Dyulgerov et al, 2018). These magmatic bodies are usually several hundred meters to kilometers in width, but regardless of their small sizes, they show variable petrographic composition, in which intermediate to acid varieties predominate.…”