Carboniferous-Permian rifting and magmatism in southern Scandinavia, the North Sea and northern Germany: a review

Abstract

During the Late Carboniferous and Early Permian an extensive magmatic province developed within northern Europe, intimately associated with extensional tectonics, in an area stretching from southern Scandinavia, through the North Sea, into northern Germany. Within this area magmatism was unevenly distributed, concentrated mainly in the Oslo Graben and its offshore continuation in the Skagerrak, Scania in southern Sweden, the island of Bornholm, the North Sea and northern Germany. Available geochemical (major- and trace-element, and Sr-Nd isotope, data) and geophysical data are reviewed to provide a basis for understanding the geodynamic setting of the magmatism in these areas. Peak magmatic activity was concentrated in a narrow time-span from c. 300 to 280 Ma. The magmatic provinces developed within a collage of basement terranes of different ages and lithospheric characteristics (including thicknesses), brought together during the preceding Variscan orogeny. This suggests that the magmatism in this area may represent the local expression of a common tectono-magmatic event with a common causal mechanism. Available geochemical (major and trace element and Sr-Nd isotope data) and geophysical data are reviewed to provide a basis for understanding the geodynamic setting of the magmatism in these areas. The magmatism covers a wide range in rock types both on a regional and a local scale (from highly alkaline to tholeiitic basalts, to trachytes and rhyolites). The most intensive magmatism took place in the Oslo Graben (ca. 120 000 km3) and in the NE German Basin (ca. 48 000 km3). In both these areas a large proportion of the magmatic rocks are highly evolved (trachytes-rhyolites). The dominant mantle source component for the mildly alkali basalts to subalkaline magmatism in the Oslo Graben and Scania (probably also Bornholm and the North Sea) is geochemically similar to the Prevalent Mantle (PREMA) component. Rifting and magmatism in the area is likely to be due to local decompression and thinning of highly asymmetric lithosphere in responses to regional stretching north of the Variscan Front, implying that the PREMA source is located in the lithospheric mantle. However, as PREMA sources are widely accepted to be plume-related, the possibility of a plume located beneath the area cannot be disregarded. Locally, there is also evidence of other sources. The oldest, highly alkaline basaltic lavas in the southernmost part of the Oslo Graben show HIMU trace element affinity, and initial Sr-Nd isotopic compositions different from that of the PREMA-type magmatism. These magmas are interpreted as the results of partial melting of enriched, metasomatised domains within the mantle lithosphere beneath the southern Olso Graben; this source enrichment can be linked to migration of carbonatite magmas in the earliest Paleozoic (ca. 580 Ma). Within northern Germany, mantle lithosphere modified by subduction-related fluids from Variscan subduction systems have provided an important magma source components.

Petrology of nepheline syenite pegmatites in the Oslo Rift, Norway: Zr and Ti mineral assemblages in miaskitic and agpaitic pegmatites in the Larvik Plutonic Complex

“…U-Pb dating of magmatic zircon suggests a relatively short period of emplacement (299-292 Ma, Dahlgren 2010), overlapping in time with the main rifting episode with widespread rhomb porphyry volcanism (Larsen et al 2008). Trace element distribution patterns and radiogenic isotopic signatures of larvikite and rhomb porphyry point towards an origin from the lithospheric mantle (Neumann et al 2004 and references therein). The rocks of the Larvik Plutonic Complex range from mildly quartz normative in the early ring intrusions, to strongly nepheline normative in the younger intrusions (Fig.…”

“…The Oslo Rift in south-eastern Norway is part of a system of late Carboniferous to Permian continental rifts in northern Europe (Neumann et al 2004). Rift-related igneous rocks range in composition from alkaline basalt to granite and nepheline syenite, with a large proportion of intermediate, monzonitic intrusive rocks (larvikite) and compositionally equivalent, latitic lavas known as rhomb porphyry (Neuman et al 2004 and references therein).…”

Evolution of the lithosphere in the area of the Rhine Rift System

“…The widespread Stephanian-Early Permian (305-285 Ma) alkaline intrusive and extrusive magmatism of the Variscan domain and its foreland is mantle-derived and locally shows evidence of crustal contamination (Bonin 1990;Bonin et al 1993;Neumann et al 1995;Marx et al 1995;Benek et al 1996;Cortesogno et al 1998;Breitkreuz and Kennedy 1999;Neumann et al 2004). Melt generation by partial melting of the uppermost asthenosphere and the lithospheric thermal boundary layer was probably triggered by a rise in the potential temperature of the asthenosphere and by its localised transtensional decompression.…”

Post-Caledonian brittle deformation in the Bergen area, West Norway: results from K–Ar illite fault gouge dating

“…The Late Carboniferous-Permian was a period of widespread rifting and locally intense magmatism in northern Europe (e.g., Neumann et al, 2004). In southern Norway, the Oslo Rift developed during this time (Neumann et al, 1992Larsen et al, 2008).…”