The diagnostic geochemistry, relative abundance, and spatial distribution of high-calcium, low-alkali olivine tholeiite dykes in the Lower Tertiary regional swarm of the Isle of Skye, NW Scotland

Abstract

SummaryDykes from four sections across the axis of the Skye regional swarm have been analysed for major elements, Nb, Rb, Sr, Y, Zr, and rare-earth elements. 70 % of the dykes are characterized by relatively high CaO (11–12%), and low abundance of elements such as TiO2 (∼1%), K2O (0·05–0·20 %), Zr (30–60 ppm), with a light-rare-earth depleted chondrite normalized pattern. The remainder of the swarm comprises dykes equivalent in composition to the Skye Main Lava Series and dykes belonging to a further magma type distinguished by a flat chondrite normalized rare-earth pattern. The high-calcium, low-alkali tholeiite dykes are confined to a narrow persistent zone forming the major axis of dilation of the swarm; other basaltic dykes are axially less persistent and have a wider lateral distribution. The more evolved dykes tend to be restricted to central Skye.