Gabbroic, Syenogabbroic and Syenitic Cumulates of the Tugtutôq Younger Giant Dyke Complex, South Greenland

  • B. G. J. Upton
Part of the NATO ASI Series book series (ASIC, volume 196)


The Tugtutôq Younger Giant Dyke Complex comprises an interconnecting suite of dykes, individually up to 800 m broad, traceable for some 145 km through a Proterozoic granitic terrain. The intrusion is thought to have resulted from one major influx of high-alumina mildly alkaline basalt and hawaiite magma at c. 1150 Ma. It has well-chilled margins grading in to coarse troctolitic gabbros. At intervals along their length the inner parts of the dykes are composed of orthocumulates in which rhythmic layering and/or feldspar lamination defines synformal pods, up to 3 km long. Among the features present are modally graded layering, isomodal layering, intermittent rhythmic layering, cross-bedding and magmatic erosion channels, including slump structures, slump breccias, down-dip thickening of mafic layers and high-temperature (annealed) faults. Cryptic and phase layering is also evident. Crystal fractionation occurred in a closed system (or systems) and the sequence of cumulus assemblages was: (i) pl+ol (ii) pl+ol+mt+il+ap (iii) pl+ol+mt +il+ap+cpx (iv) AF+ol+mt+il+ap+cpx. ‘Conventional names’ for the cumulatė rocks are troctolite (with picritic and anorthositic facies), ferro-syenogabbro, ferro-syenite and syenite. The parent magma was critically undersaturated and both quartz syenites and nepheline syenites. are represented among the residual differentiates. Marginal gabbroic facies to the layered synforms can display near-vertical mafic layering, perpendicular feldspar rock and approximations to Skaergaardstyle ‘wavy pyroxene’ facies. Large xenoliths of layered anorthosite cumulates in the intrusion indicate the presence at depth of further cumulate suites crystallised from high-alumina, mildly alkaline, basaltic magma.


Nepheline Syenite Alkali Feldspar FeTi Oxide Plane Polarise Light Border Group 
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  1. Becker SM (1984) Petrology of the Giant Dykes of Isortoq and Feldspar variation in the Klokken Complex, South Greenland. Unpubl PhD thesis, Univ of AberdeenGoogle Scholar
  2. Bichan R (1974) The evolution and structural setting of the Great Dyke, Rhodesia. In Clifford TN & Gass IG (eds) African magmatism and tectonics. Edinburgh: Oliver & Boyd, 51–71Google Scholar
  3. Bird DK, Rosing MT, Manning CE, Rose NM (1985) Geologic fieldGoogle Scholar
  4. studies of the Miki Fjord Area, East Greenland. Bull geol Soc Denmark, 34: 219–236Google Scholar
  5. Bridgwater D (1967) Feldspathic inclusions in the Gardar igneous rocks of south Greenland and their relevance to the formation ofGoogle Scholar
  6. major anorthosites in the Canadian Shield. Can J Earth Sci 4: 995–1014Google Scholar
  7. Bridgwater D, Coe K (1970) The role of stoping in the emplacement of the giant dykes of Isortoq, South Greenland. Geol J spec Issue 2: 67–78Google Scholar
  8. Engell J, Pedersen S (1975) Rubidium-strontium whole rock isochron age determination from the Bangs Havn intrusion, South Greenland. Bull geol Soc Denmark 23: 130–133Google Scholar
  9. Irvine TR (1982) Terminology for Layered Intrusions. J Petrology 23: 127–162CrossRefGoogle Scholar
  10. McClay KR, Campbell IH (1976) The structure and shape of the Jimberlana intrusion, western Australia, as indicated by anGoogle Scholar
  11. investigation of the Bronzite Complex. Geol Mag 113: 129–139Google Scholar
  12. Martin AR (1985) The evolution of the Tugtutôq-Ilímaussaq Dyke Swarm, Southwest Greenland. Unpubl PhD thesis, Univ of EdinburghGoogle Scholar
  13. Patchett PJ, Hutchinson J, Blaxland AB, Upton BGJ (1976) Origin of anorthosites, gabbros and potassic ultramafic rocks from the Gardar Province, South Greenland: Sr isotopic ratio studies. Bull geol Soc Denmark 25: 79–84Google Scholar
  14. Upton BGJ, Emeleus CH (1986) Mid-Proterozoic Alkaline Magmatism in Southern Greenland: The Gardar Province. In The Alkaline Rocks: A review. Fitton JG & Upton BGJ (eds)Google Scholar
  15. Upton BGJ, Fitton JG (1985) Gardar dykes north of the Igaliko Syenite Complex, southern Greenland. The Geological Survey of Greenland Report N° 127: 24 ppGoogle Scholar
  16. Upton BGJ, Stephenson D, Martin AR (1985) The Tugtutóq Older Giant Dyke Complex: Mineralogy and Geochemistry of an alkali-gabbro - augite-Google Scholar
  17. syenite - foyaite association in the Gardar Province of South Greenland. Mineralog Mag London, 49: 623–642Google Scholar
  18. Upton BGJ, Thomas JE (1980) The Tugtutóq Younger Giant Dyke Complex, South Greenland: Fractional Crystallisation of Transitional Olivine Basalt Magma. J Petrology 21: 167–198Google Scholar
  19. Wager LR, Brown GM (1968) Layered Igneous Rocks, Edinburgh: Oliver & Boyd Ltd.Google Scholar
  20. Yoder HS, Tilley CE (1962) Origin of basalt magma: an experimental study of natural and synthetic rock systems. J Petrology 3: 342–532.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 1987

Authors and Affiliations

  • B. G. J. Upton
    • 1
  1. 1.Department of GeologyUniversity of EdinburghEdinburghUK

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