Permo-Carboniferous magmatism of the Northeast German Basin

Abstract

Variscan continent-continent collision in Central Europe was followed by a period of syn- to late-tectonic magmatism involving the extrusion of large volumes of Permosilesian-age volcanic rocks, particularly in the Northeast German Basin. The volcanic suite (up to ca. 2000 m thick) comprises rhyolites, acid and basic andesites, and tholeiitic and alkali basalts. Tectono-geochemical analysis, in conjunction with volume calculations and petrography reveals changes in volcanic activity over time. A total of five eruptive stages are recognised beginning in the Stephanian and extending up into the Upper Rotliegend (Permian). These include: the Stephanian (Late Carboniferous) (andesite) pre-ignimbrite stage (I), Lower Rotliegend (Permian)-age (explosive) ignimbrite stage (II), post-ignimbrite stage (III), late rhyolite stage (IV), and, Upper Rotliegend (Permian)-age late basalt stage (V). In addition, several volcanic centres including at least two large caldera-like structures are recognised. The total calculated volume for the Northeast German Basin volcanics is ca 48,000 km 3, comprising rhyolitic rocks and ignimbrites (ca. 70%), andesitic rocks (ca. 26%) and basalts with cogenetic dolerites (ca. 4%). Regional variations in composition and geochemistry are related to diverse crust-mantle regimes which correlate with differing positions relative to the heterogeneous basement of the Variscan foredeep or within the Rhenohercynian orogenic zone. The crustal thickening and increasing generation depth of the mafic magmas from north to south may reflect the presence of a pre-existing subduction-influenced basaltic magma source.