The geochemistry of Lower Tertiary basic dykes in the Eastern Red Hills district, Isle of Skye, and their significance for the proposed magmatic evolution of the Skye Centre

AbstractMajor- and trace-element data are presented for basic dykes intruding the Eastern Red Hills district of the Tertiary igneous centre of Skye. In addition to a group of transitional basic intrusions, members of two other distinctive suites have been identified: (1) a series of basic alkaline intrusions (akin to the ‘Beinn Dearg Type’ of Harker, 1904), with characteristic high alkali contents, distinctive values of K2O/(K2O + Na2O) and rare-earth-element (REE) patterns similar to those of many of the Tertiary lavas of north Skye, and, (2) tholeiitic dykes, with low concentrations ofK2O, Ti/Zr values of c. 100, and flat REE patterns similar to those of the so-called Fairy Bridge magma type (Mattey et al., 1977). From these data and a consideration of the time relationships of the various components of the Skye Centre, agreement is found with Thompson et al.'s (1972, 1980) model of a mantle thermal anomaly which generates the magmatic sequence: transitional basic magmas, giving way to olivine-bearing tholeiitic magmas (at the culmination of the anomaly), and, finally, late-stage basic alkaline magmas at the end of the activity.