The lavas and minor intrusive rocks from the Jurassic volcanic province of the Forties-Piper area of the North Sea can be subdivided into three distinct series on the basis of petrography, whole-rock chemistry and mineral chemistry. These series, which probably evolved from one or more alkali olivine basalt parent magmas are: (i) an ankaramite-basaltic hawaiite-hawaiite series, (ii) an alkali olivine basalt-hawaiite series, and (iii) an intrusive hawaiite-intrusive mugearite series. Variations within series are due mainly to differential distribution of mafic phenocryst phases but liquid immiscibility and magmatic fractionation are also believed to have contributed. The Middle Jurassic volcanism in the North Sea area is thought to be related to the tensional tectonic regime which existed in NW Europe during the Jurassic or to be due to a region of high heat flow extending northeastwards from the contemporary spreading axis between Iberia and Newfoundland and possibly to a combination of the two.

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