The Gardar Alkaline Igneous Province is a Proterozoic, rift-related, province in south-west Greenland. It consists of lavas, central complexes and dyke swarms, dating from 1350 and 1150 million years ago. The majority of the intrusives were emplaced into a Proterozoic mobile belt which formed during the Ketilidian orogeny at -1850- 1740 Ma, but the north-western part of the province transgressed onto the edge of the South Greenland Archaen craton, and it is this area which has been under study. Fieldwork has been carried out as part of the present project. The Gardar intrusives within the craton include three central complexes, Grennedal-Ika, Ivigtut and Kungnat, as well as many dykes. Gronnedal-Ika is the oldest of the complexes, and consists of nepheline syenites cut by a carbonatite plug. The oldest dykes in the area are lamprophyres; these were succeeded by various groups of basic and alkaline salic dykes, including a major set of olivine dolerites known as the "Brown Dykes". The Ivigtut stock is an alkali granite which, prior to mining, contained the world's largest deposit of cryolite, and the granite shows as distinctive pattern of alteration related to the fluids from which the ore deposit formed. The Kungnat Complex consists of saturated and over-saturated syenites with an alkali grabbro ring-dyke. The petrography of the different rock-types is described together with the mineralogy of the Ivigtut granite. It is concluded that the lamprophyre magmas of the Gardar formed as volatile-rich small-degree partial melts within the asthenosphere, which were intruded with minimal lithospheric contamination. Larger volumes of melt were derived from lithospheric mantle which had been selectively enriched in incompatible elements, possibly through the action of fluids derived from a subducting slab at the close the of the Ketilidian orogeny. These melts were intruded as primitive dykes, or evolved through fractionation and variable crustal contamination to produce the spectrum of Gardar magmas.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:651596 |
| Date | January 1997 |
| Creators | Goodenough, Kathryn |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13933 |
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