Linking changes in tectonic style with magmatism in northern Europe during the late Carboniferous to latest Permian

Early Carboniferous to Permian magmatism associated with rifting within the northern foreland of the Variscan Orogen was widespread across Europe. During the long period of magmatic activity the regional tectonic setting changed across the region from early Carboniferous extension and basin formation to a rifting–wrenching style of deformation in the late Carboniferous (Stephanian) to early Permian. Wrenching and faulting were accompanied by widespread, voluminous and episodic magmatic extrusion, intrusion and underplating. This was followed by thermal relaxation and the development of the Northern and Southern Permian Basins in later Permian times. Thermal relaxation was punctuated by a Permo-Triassic phase of extension and graben formation. 40Ar/39Ar Ar step-heating dating for mineral separates and whole-rock samples of magmatic rocks from southern Scandinavia (Oslo Graben and south Sweden) and Rügen (north Germany) provides further radiometric evidence for three of the proposed periods of magmatic activity in the region. Latest Carboniferous to earliest Permian ages (c. 300–310 Ma) were obtained for volcanic rocks in the Oslo Graben and dolerite sills and dykes in south Sweden and north Germany. This phase can be time-correlated with magmatic activity that occurred throughout Europe during large-scale dextral wrenching that followed the Variscan Orogeny. A second phase of alkaline intrusions is confined to the Oslo Graben and related to caldera collapse around c. 275 Ma. The third, Permo-Triassic phase (c. 250 Ma) is considered to be related to a new tectonic cycle involving extension that triggered minor melting of enriched, fertile mantle.