| Summary: | A research report submitted at the Faculty of Science, University of the Witwatersrand, Johannesburg for the Degree of Master of Science (Geology), 2019 The Singertât Complex forms part of the Skjoldungen Alkaline Igneous Province (SAIP, 2760-2690 Ma) located in SE Greenland. It was emplaced into the southern part of the SAIP in a sequence of small, sheet-like intrusions during the Late Archean and was thought until recently to be post-tectonic with previous work suggesting an age of 2680-2660 Ma. The complex consists of a variety of silica undersaturated (nepheline-bearing) alkaline rocks, which occur as modally layered, horizontal sheets cut by minor late-stage nepheline syenite pegmatites and carbonatites. This project aims to understand the petrogenesis of the Singertât Complex, including investigating magmatic processes and crystal cargo dynamics from mantle source to final emplacement in the upper crust. Crucial questions include whether the complex is constructed from single or multiple magma batches, whether those batches were emplaced as crystal-poor liquids or as crystal mushes and what type/s of crystallization processes operated? Detailed petrographic analysis indicates that the Singertât Complex is composed primarily of nepheline-bearing lithologies such as urtite (>70% nepheline), ijolite (70-30% nepheline) and melteigite (<30% nepheline). These alkaline silicate rock types are either equigranular or porphyritic and the main mineral phases include nepheline, orthoclase, microcline, anti-perthite, aegerine-augite, biotite, minor primary carbonate and in some samples sodalite, with accessory magnetite, apatite and zircon. Poikilitic growth relationships suggest that mafic minerals crystallized first followed by nepheline, which appears to have crystallized from the remaining interstitial liquid. Anti-perthite commonly exhibits anastomosing exsolution textures, indicating supersolvus crystallization temperatures above 600 ºC, followed by slow cooling. Both gradational transitions and sharp ...
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