Magmatic evolution of the Skye igneous centre, western Scotland: Modelling of assimilation, recharge and fractional crystallization

The Skye igneous centre, forming part of the British Tertiary magmatic province, developed over a similar to7 Myr period (61-54 Ma) and is characterized by a complex suite of lavas, hypabyssal and intrusive rocks of picritic to granitic composition. The intrusion of magma from mantle to crust at similar to2x10(-3)km(3)/yr (6 Mt/yr) advected magmatic heat of roughly 0.2 GW averaged over the period of magmatism supporting an 'excess' heat flux of about 130 mW/m(2), or about twice the present-day average continental heat flow. The volume of new crust generated at Skye (similar to15000 km(3)) spread over the present-day area of Skye corresponds to similar to9 km of new crust. The geochemical evolution of the Skye magmatic system is constrained using the Energy-Constrained Recharge, Assimilation, and Fractional Crystallization (EC-RAFC) model to understand variations in the Sr- and Pb-isotopic and Sr trace-element composition of the exposed magmatic rocks with time. The character (composition and specific enthalpy) of both assimilant and recharge magma appears to change systematically up-section, suggesting that the magma reservoirs migrated to progressively shallower levels as the system matured. The model of the magma transport system that emerges is one in which magma batches are stored initially at lower-crustal levels, where they undergo RAFC evolution. Residual magma from this stage then migrates to shallower levels, where mid-crustal wall rock is assimilated; the recharge magma at this level is characterized by an increasingly crustal signature. For some of the stratigraphically youngest rocks, the data suggest that the magma reservoirs ascended into, and interacted with, upper-crustal Torridonian metasediments.