The Late Paleozoic igneous suite between the Saxon granulite massif and the Altmark, central Germany: Petrogenetic and mineralogical constraints on the post-orogenic magma evolution

The Late Paleozoic continental rift in the area of central Europe set the stage for intense magmatic activity, apparent in plutonic complexes (e.g. Brocken, Pretzsch-Prettin), large subvolcanic bodies (e.g. Halle laccoliths, Wurzen porphyries), and recorded by voluminous pyroclastic sheets in numerous caldera systems (e.g. Wurzen, Rochlitz, and Flechtingen ignimbrites). Since up to now, their petrogenetic evolution often remains veiled in mystery or is still under debate. Focussing on this post-Variscan magmatic flare-up, the obtained geochemical and mineralogical data set depicts selected magma reservoirs, their evolution, and storage.

The different compositions of the Cadomian to Variscan basement and the longevity of magma chambers set within these particular regions have a decisive influence on the geochemical characteristic. In detail, metasedimentary rocks (e.g. metamorphosed graywacke, mica schist) are most often directly responsible for Al₂O₃-supply and subsequently lead to corundum-normative magmas. The highest amount of normative corundum (up to 3.1 wt%) can be found in the Flechtingen ignimbrite, which magma system was capable of crystallizing almandine garnet (Ca_0.03Fe_0.84Mg_0.13)₃Al₂Si₃O₁₂) in lower crustal levels (>7 kbar ≙ 25 km). A similar picture emerges within the subordinated diopside-normative parts of the Wurzen volcanic rocks (up to 3.28 wt%), where crystallization of calcic clinopyroxene took place at 6 to 10 kbar (≙ 22 to 36 km). Here, it is proposed that parental diopside normative alkaline to tholeiitic and garnet-bearing magmas are fast ascending and mingled into upper crustal magma bodies.