Crystallization and Differentiation Processes in the Thin Layered Alkali Gabbroic Intrusions of the Ulvö Gabbro Complex,

Fractional crystallization of magma is a commonly invoked mechanism for chemical differentiation in systems that range from volcanoes to entire planets. However, the processes that control separation of crystals and liquids in natural systems remain controversial, since the dynamics of crystallizing magma chambers cannot be studied directly. Currently popular models involve strictly mechanical separation processes e.g., crystal settling and compositional convection. In this thesis, however, it is demonstrated that a disequilibrium process can result in very effective fractional crystallization. The ~1265 Ma Norra Ulvön Gabbro (NUG) is a ~300 m thick alkali gabbroic saucer-shaped sill in central Sweden that belongs to the Ulvö Gabbro Complex. The NUG is strongly differentiated, displays well developed modal layering, and has not experienced metamorphic alteration. A stratigraphic section through this intrusion has been studied in detail, including major and trace-element whole-rock analysis and in situ mineral analysis. Laser-ablation inductively coupled plasma mass spectrometr