Layering in the Ilimaussaq alkaline intrusion, South Greenland

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Authors:Sorensen, Henning; Larsen, Lotte Melchior
Author Affiliations:Primary:
Univ. Copenhagen, Inst. Petrol., Copenhagen, Denmark
Other:
Geol. Surv. Greenland, Denmark
Volume Title:Origins of igneous layering
Volume Authors:Parsons, Ian, editor
Source:NATO Advanced Study Institutes Series. Series C: Mathematical and Physical Sciences, Vol.196, p.1-28; NATO Advanced Research Workshop on Origins of igneous layering, Narsarsuaq, Greenland, Aug. 4-15, 1986, edited by Ian Parsons. Publisher: D. Reidel Publishing Company, Dordrecht-Boston, International. ISSN: 0377-2071
Publication Date:1987
Note:In English. Contrib. to the mineralogy of Ilimaussaq, No. 82. 37 refs.; illus. incl. 1 table, sects., geol. sketch map
Summary:The Ilimaussaq alkaline intrusion shows various types of igneous layering. Inch-scale layering occurs in the least-differentiated rocks-augite syenite and pulaskite-and is probably caused by a nucleation-diffusion mechanism. Pegmatitic layering is found in the roof series of the agpaitic rocks (foyaite and naujaite) and is considered to have formed by upward concentration of volatiles under the downward crystallizing roof. They indicate that the magma tended to become compositionally zoned. Isomodal layering is found in naujaite and especially in the latest rocks, the lujavrites. The origin of this type of layering is still unsolved. Mineral graded layering is found in the floor series of kakortokite and in some lujavrites. It has mostly been studied in the kakortokite series- one of the best known examples of mineral-graded layering and macrorhythmic layering. The mineralogy of the kakortokite series is described, and theories of formation of the layering reviewed. Crystallization probably took place in a stagnant bottom layer, and the layering is considered to be caused by different nucleation and growth maxima in relation to the degree of undercooling of the minerals in a multiply saturated magma. The mineral grading is enhanced by density during settling of the crystals. (Author's abstract) [A.W.H.]
Subjects:Alkali granites; Alkalic composition; Chemical composition; Cross-stratification; Crystallization; Granites; Igneous rocks; Intrusions; Kakortokite; Layered intrusions; Mineral composition; Nepheline syenite; Pegmatite; Petrology; Planar bedding structures; Plutonic rocks; Precambrian; Sedimentary structures; Syenites; Upper Precambrian; Arctic region; Greenland; Ilimaussaq; South Greenland; Evolution; Gardar
Abstract Numbers:88M/1186
Record ID:1988015648
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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