Sr and Pb IsotopeMicro-analysis of Plagioclase Crystals from Skye Lavas: an Insight into Open-system Processes in a Flood Basalt Province

Crystals in many magmatic rocks are heterogeneous in terms of their isotope composition. Detailed crystal-isotope stratigraphy (CIS) studies have shown that crystals act as reliable recorders of their magma source composition and of the pathways of magma interaction, and successfully identify the end-members involved in magmatic systems. In this paper we have analysed cores and rims and single plagioclase crystals from samples of the Skye Volcanic Centre, part of the British Palaeogene Igneous Province. The isotope analyses reveal that plagioclase crystals from different volcanic samples through the lava succession in Skye (Skye Main Lava Series, Preshal More Basalts and Big-Feldspar Lavas) have larger Sr and Pb isotopic ranges than the isotopic ranges found in hundreds of whole-rock analyses. The large Sr and Pb isotopic variation in plagioclase crystals in Skye is due to variable degrees of crustal contamination of the parental magmas during fractional crystallization and during the ascent of such magmas to the surface. The isotope variation of plagioclase crystals in the early lavas (Skye Main Lava Series) reflects assimilation-fractional crystallization processes dominated by the lower crust, whereas plagioclase crystals from later erupted magmas (Big-Feldspar Lavas and Preshal More basalts) show assimilation of upper crust superimposed on previous lower crustal contamination processes. The variability in Sr and Pb isotopes documented in different crystals within the same rocks shows that the crystals have been aggregated in magmas from different sites of storage and differentiation during the ascent of the magmas to the surface. © The Author 2008. Published by Oxford University Press. All rights reserved.