HR: 0830h
AN: V31E-0975    [PDF]
TI: Magmatic Evolution of the Skye Igneous Center, Western Scotland
AU: * Fowler, S J
EM: sfowler4@jhem.jhu.edu
AF: Department of Geological Sciences, Central Washington University, 400 E. University Way, Ellensburg, WA 98926 United States
AU: Bohrson, W A
EM: bohrson@geology.cwu.edu
AF: Department of Geological Sciences, Central Washington University, 400 E. University Way, Ellensburg, WA 98926 United States
AU: Spera, F J
EM: spera@geol.ucsb.edu
AF: Department of Earth Sciences and Institute for Crustal Studies, UC Santa Barbara, Building 526, Santa Barbara, CA 93106 United States
AB: Geochemically complex igneous suites are the result of interplay between deep and crustal-level processes. Quantitatively modeling the contribution that crustal-level processes such as magma recharge, crustal assimilation, and fractional crystallization have is critical for developing realistic models of how magma transport/storage systems evolve. The Energy-Constrained Recharge, Assimilation, and Fractional Crystallization simulator (EC-RAFC, Spera \& Bohrson, 2001, 2002; Bohrson \& Spera, 2001, 2003) provides a means to model thermal, compositional, and magma volume data for complex magmatic systems. The Skye igneous center, western Scotland, spanning the period 60.53 $\pm$ 0.08 Ma - 53.5 $\pm$ 0.8 Ma and characterized by a well-documented suite of lavas and intrusive rocks of picritic to granitic composition, is the first natural data set to which the EC-RAFC model has been applied in detail. Based on analysis of published field, stratigraphic, petrographic, and chemical data, we propose that the Skye Tertiary magmatic sequence be divided into four petrogenetically related lineages. EC-RAFC results indicate that each lineage is characterized by a unique parental magma that has undergone distinct episodes of RAFC. Model results, constrained by published data on the nature of the crust beneath Skye, indicate that the character of the assimilant changes upsection, suggesting that the associated magma reservoirs migrated to shallower levels as the magmatic system matured. The magmatic products of each group also record the fingerprint of multiple episodes of magma recharge, where the character of the recharge magma also evolves with time. The image of the magma transport system that emerges is one in which magma is initially intruded at lower crustal levels and undergoes a distinct RAFC episode. Residual magma from this event then migrates to shallower levels, where mid-crustal wallrock is assimilated; recharge magma is characterized by increasingly crustal chemical and thermal signatures. For some of the stratigraphically youngest rocks, results also suggest that magma reservoirs ascended into and interacted with upper crustal sediments. While the quantitative details provided by the Skye simulations support the hypothesis that the Skye igneous center can be characterized by a relatively small number of compositionally similar parental magmas to which complex RAFC processes occur, they also allow detailed predictions to be made about the geochemical, thermal and magma volume characteristics of the magmatic system. Further study that builds on these predictions at locations such as Skye promise to enhance our understanding of the evolution of complex magmatic systems on Earth.
UR: http://magma.geol.ucsb.edu/
DE: 3230 Numerical solutions
DE: 3640 Igneous petrology
DE: 3670 Minor and trace element composition
DE: 3939 Physical thermodynamics
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting