Geochemical constraints on the late-stage evolution of basaltic magma as revealed by composite dikes within the Kangâmiut dike swarm, West Greenland
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The Kangâmiut dike swarm in West Greenland contains numerous composite dikes with mafic margins and andesitic centers. Internal chilled margins show that the andesitic centers intruded into the middle of the mafic dikes. Major element systematics indicate that the fractionation of olivine, clinopyroxene, plagioclase and Fe-Ti oxides drove the evolution of the Kangâmiut parental magma during its transition from mafic to andesitic compositions. Incompatible trace elements show a marked relative decrease in middle and heavy rare-earth elements (REE) between the mafic margins and the andesitic centers. The decrease in the REE is not explicable by olivine, clinopyroxene, plagioclase and Fe-Ti oxide fractionation or by the fractionation of the accessory phases apatite, zircon or garnet. Rb-Sr and Sm-Nd isotopes from margin and center pairs from these composite dikes are nearly identical indicating that crustal contamination had little to no affect on their evolution. Trace element modeling utilizing the mixing of evolved Kangâmiut magmas and low degree melts derived from partial melting of garnet lherzolite produce excellent fits with the trace element patterns for the andesitic centers. These models suggest that the late-stage evolution of the Kangâmiut dikes included input of mantle melts produced during the end stages of rifting.
|Number of pages||11|
|Publication status||Published - 2008|
We gratefully acknowledge Flemming Mengel, and the late David Bridgwater for their help and insights during the early stages of this research. David Bridgwater's previous work on these composite dikes served as an important foundation for this current work and we are thankful for his enthusiastic support of our efforts. The manuscript also benefited from thorough and constructive reviews from Nicholas Arndt and an anonymous reviewer. This work was partially funded by the Danish Lithosphere Center and grants from the National Science Foundation (OCE-9811453 and EAR-970667).
- Composite dikes, Dike swarm, Greenland, Magma mixing