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 macrodykes of the Kangerdlugssuaq area, East Greenland are among a large number of tholeiitic intrusions emplaced into Archean crust and Tertiary volcanic rocks along the East Greenland margin during the initial stages of Tertiary rifting of the North Atlantic basin. These intrusions are spectacularly exposed in the glaciated terrain along the Blosseville Coast and preserve evidence of complex interaction with their volcanic, sedimentary and gneissic host rocks. The available chemical data on these intrusions indicate that these magmas were selectively contaminated by components of the lower crust and hydrothermally altered mafic volcanics and that magmatic processes led to chemical stratification within these intrusions. Various scales and modes of crustal contamination are revealed along the intrusive contacts. These exposures permit detailed structural and chemical study of the hybridization process. Field and geochemical studies of these intrusions are proposed to assess the roles of fractionation and assimilation in the chemical evolution of these magmas and appropriate models will be developed to describe these relations as constrained by experimental phase equilibria and kinetic data obtained using natural materials of the macrodykes. The results from this "case study" will be used to evaluate the role of crustal contamination during chemical evolution of associated gabbroic complexes and contemporaneous East Greenland basalts and place constraints on the source regions for these magmas.