Jurassic volcanism in Skåne, southern Sweden, and its relation to coeval regional and global events

Abstract

Isolated exposures of basalt in a 1000 km2 area in the central northern part of Skåne have long been known to the local people. A volcanic origin for these rocks was finally resolved by geologists during the early 1800s. Until 1965 the volcanic activity was considered to have occurred during the Cenozoic i.e. not older than 65 Ma. In the 1970s attempts were made to directly date the volcanic activity using the K/A radiometric technique. The obtained dates suggested a much older eruption age namely during the Jurassic-Cretaceous. This paper presents 40Ar/39 Ar geochronological data from eight volcanic necks revealing evidence for two distinct pulses of volcanic activity in this region of Skåne. The first and the main volcanic phase occurred in the Early Jurassic (late Sinemurian to Toarcian) at 191-178 Ma, some 20-30 million years older than previously reported. The second pulse occurred in the late Early Cretaceous (Albian) at 110 Ma. The similar geochemical composition of the basalts from this region despite the long eruption span of approximately 80 million years and the occurrence of repeated tectonic movements in the region favours the following hypothezised mechanism - intermittent release of eutectic melts caused by tectonic decompression of the lithospheric mantle. Similar processes have been proposed for the coeval North Sea volcanism. On a global scale the tectonic movements in the Earth's crust during the Mesozoic are linked to the break-up of the supercontinent Pangea. Apart from generating volcanic events in Skåne and the North Sea more voluminous coeval volcanism occurred in the Karoo and Ferrar volcanic provinces in the Southern Hemisphere.