Petrology of the giant dykes of Isortoq and feldspar variation in the Klokken complex, south Greenland
Part One of the thesis deals with the bulk rock chemistry (investigated by XRF) and mineral compositions (investigated by microprobe) of olivine, pyroxene, amphibole, feldspar and accessory minerals of the Isortoq Giant Dykes which were emplaced during Late Gardar times (~ 1200 Ma) into the Julianehaab granite basement of South Greenland, probably as feeders to surface volcanoes in a rift setting. The mechanisms of emplacement and the role of assimilation and contamination by crustal material is investigated. The development of the mildly alkaline rock suite from gabbro to syenite is discussed with reference to fractionation, mixing of liquids and crystals, crystallization at varying degrees of supercooling and interaction with the wall rock. The importance of late stage, probably largely magmatic, fluids is assessed. The second part of the thesis describes the X-ray diffraction properties and bulk chemistry of a series of alkali feldspars from the layered Klokken syenite complex. Inter- and intra-grain bulk chemical variation is established, together with cryptic variation, and the X-ray diffraction properties are related to observation made using transmission electron microscopy.