Chemical Interactions Between Gabbros and Their Host Rocks: Field and Laboratory Studies of the Tertiary Macrodikes of the Kangerdlugssuaq Area, East Greenland

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The Tertiary gabbroic dikes of the Kangerdlugssuaq region, East Greenland, offer for study the products of a natural laboratory experiment on the chemical and physical processes that occur when mafic magmas incorporate blocks of wall rocks. A combination of superb glaciated alpine outcrops, structural relief of 1 km, and good background studies of field relations and igneous petrology (including the classic work of Wager, Deer, and others on the Skaergaard Intrusion) make this an ideal study area. It should be possible to make a definitive test of the competiting hypotheses of wholesale vs. selective chemical contamination. The mechanisms of chemical interaction and mechanics of mixing hybrid magmas may be determined by direct observation of the abundant, remarkably clean outcrops. It is proposed to use a multi-disciplinary array of methods including field, geochemical, isotopic, and experimental techniques to test the hypothesis that gabbros were selectively contaminated by remobilized sialic basement and hydrothermally altered basalt wall rocks. The geochemical data will be used to evaluate existing models of assimilation - fractional crystallization and to refine such models, if necessary. The results should materially aid understanding the physics and chemistry of crustal contamination, a process essential to the accurate interpretation of geochemical characteristics of continental volcanic rocks and consequent deductions regarding the nature of subcontinental mantle.