Magmatism in the Netherlands: expression of the northwest European rifting history

The presence of igneous rocks in about 100 wells drilled for hydrocarbons, mainly concentrated in the eastern provinces of the Netherlands, the western onshore and offshore areas and in the northern offshore testify to the significance of magmatic activity in the geological history of the Netherlands. Intrusive rocks, mainly emplaced into Carboniferous and younger sedimentary rocks dominate over lavas and other extrusive products. Prominent exceptions are two buried Late Jurassic volcanoes. The Zuidwal volcano under the Waddenzee consists of thick extrusive deposits and associated subsurface features that collectively define a well-developed volcanic centre. The recently discovered Mulciber volcano is a complex on the rim of the Central Graben below the North Sea. Radiometric ages have been determined on samples from 25 wells, but most of the currently available results are inaccurate due to ubiquitous effects of alteration. Despite this limitation, additional stratigraphic, geochemical and petrological evidence indicates that magmatism in the Netherlands was largely periodic and followed a pattern of intermittent activity in the North Sea region and adjacent areas in late Paleozoic, Mesozoic and Cenozoic times. Samples from ca. 15 core intervals studied in detail suggest that a large majority of igneous rocks in the Dutch subsurface have a mafic composition and a moderate to high alkali content. Geochemical signatures are consistent with a within-plate tectonic setting throughout the successive episodes of magmatism, of which the Carboniferous – early Permian and Late Jurassic periods were the most productive. The lithospheric rifting processes that have dominated the northwest European geological history since Paleozoic times provided favourable conditions for melt generation, the emplacement of intrusive magma bodies and associated volcanism.