Geochemical evidence for the emplacement of the Whin Sill complex of northern England

Abstract The Whin Sill comprises a major quartz tholeiite sill of late Carboniferous age underlying an area of c. 5000 km 2 and with a volume of c. 200 km 3 , associated with contemporaneous dykes emplaced within Carboniferous sedimentary rocks in northeast England. New trace element analyses of chilled margins, sill interiors and dykes indicate that the Whin Sill complex magmas show significant chemical variations in terms of the relatively stable trace elements Th, Ce, Y, Zr, Nb and Ni. These data indicate that the complex was fed by a large number of compositionally distinct magma pulses, and that certain of the dykes may have formed feeder channels for the sill. The chemical characteristics of the sill and dyke samples are consistent with derivation by extensive polybaric fractional crystallization of olivine tholeiite magma derived by partial melting of compositionally heterogeneous mantle peridotite and/or crustal contamination of mantle-derived magmas.