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Most of the flows in the Palaeocene lava pile remnant of Skye are members of the Skye Main Lava Series (SMLS), comprising transitional basalts and two associated suites of evolved lavas. The first suite evolves through Fe-rich hawaiites and mugearites to benmoreites, and the second suite evolves through Fe-poor intermediates to trachytes. Ca-rich, alkali-poor olivine tholeiites (the Preshal Mhor magma type) occur as sparse flows in the stratigraphically highest parts of the lava pile remnant and are abundant in the dyke swarm transecting it. Initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios ranging from 0.70308 to 0.70571 in 45 SMLS samples show no significant correlation with degree of zeolitization (H<sub>2</sub>O<sup>+</sup>), silica saturation, or <sup>87</sup>Rb/<sup>86</sup>Sr. A moderately good negative correlation with total Sr confirms published Pb-isotope evidence of interaction with ancient, sialic crust. Details of the (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>l</sub> versus Sr pattern are consistent with previous hypotheses that the SMLS basalt-benmoreite suite evolved at a depth near the Moho, whilst the low-Fe trend to trachyte resulted from near-surface basalt fractionation.(<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>l</sub> values ranging from 0.70307 to 0.70621 for Preshal Mhor basalts show a strong positive correlation with total Sr, consistent with a model of extensive fractionation within the upper crust of a mantle-derived low <sup>87</sup>Sr/<sup>86</sup>Sr-low Sr magma, which became progressively contaminated with comparatively radiogenic crustal Sr. The lowest measured (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>l</sub> values of 0.70307 and 0.70308, for a Preshal Mhor basalt and for an SMLS basalt respectively, are consistent with the hypothesis that these two magma types were produced by successive phases of partial melting from a single volume of upper mantle.(<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>l</sub> values for additional miscellaneous basaltic lavas, dykes and major intrusives from Skye and from nearby Isle of Mull exhibit considerable variability within the range 0.7038 to 0.7072, whilst three basaltic dykes from Northern England are in the range 0.7089 to 0.7123. The latter values overlap with published (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>l</sub> values for some of the granites in the Tertiary Province of northwest Scotland and indirectly remove objections based on Sr-isotopic arguments to the genesis of the granites by fractionation of basalt contaminated with crustal Sr, but neither prove this nor disprove large-scale crustal partial fusion. |
