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The Tugtutôq older giant dyke complex: mineralogy and geochemistry of an alkali gabbro-augite-syenite-foyaite association in the Gardar Province of South Greenland

Published online by Cambridge University Press:  05 July 2018

B. G. J. Upton ,
D. Stephenson  and
A. R. Martin
B. G. J. Upton
Affiliation:
Grant Institute of Geology, University of Edinburgh, Edinburgh EH9 3JW
D. Stephenson
Affiliation:
British Geological Survey, Murchison House, Edinburgh EH9 3LA
A. R. Martin
Affiliation:
Grant Institute of Geology, University of Edinburgh, Edinburgh EH9 3JW
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Abstract

The Older Giant Dyke Complex is a differentiated alkaline intrusion of Proterozoic age (1154±16 Ma) and is the earliest of the late Gardar intrusions in the Tugtutôq-Ilímaussaq region. The dyke is approximately 20 km long by 0·5 km broad and comprises (i) marginal ‘border group’ rocks of alkali olivine gabbro, grading inwards to ferro-syenogabbro and (ii) an axial ‘central group’ of salic rocks ranging from augite syenite in the WSW to sodalite foyaite in the ENE.

Chilled margins contain plagioclase (An53), olivine (Fo53), magnetite, ilmenite, and apatite as liquidus phases and later-crystallized augite (Di69Hd27Ac4) and biotite (Annite32). The coexisting Fe-Ti oxides indicate fO2 and T values just below the synthetic QFM buffer curve. In the border group, plagioclase cores zone into anorthoclase and soda-sanidine rims, olivines reach Fo16, pyroxenes Di32Hd59Ac9, and biotites Annite86. Interstitial pargasitic amphibole appears close to the innermost margins. In the central group, feldspars are all perthitic alkali feldspars and nepheline becomes a major, early crystallizing phase. Olivines range from Fo10-Fo4, in the augite-syenites where they coexist with ferro-salites Di50Hd47Ac3, but olivine is absent from foyaitic assemblages in which the pyroxenes range through aegirine-augite to pure aegirine. Interstitial amphiboles range from ferro-pargasite or hastingsite to katophorite and thence towards arfvedsonite, but are absent from the most differentiated rocks, whereas biotite occurs throughout the entire group in the range Annite71-Annite100.

The parental magma, represented by the chilled margins, was a relatively anhydrous alkali olivine-basalt with an initial 87Sr/86Sr ratio of 0.70326. Its high Ti, P, Ba, and F contents are inferred to be features inherited from a primary magma, derived from the mantle as a small partial melt fraction which involved significant amounts of fluor-apatite and phlogopite. While all lithologies are considered as differentiates from this parental magma, there is both a well-defined field junction and a compositional hiatus between the border group and the central group rocks. Mineralogical considerations and REE patterns suggest that the later, more salic (?benmoreitic) magma from which the central group crystallized, related to the parental magma by ol-fsp-ap-FeTi oxide fractionation. Congelation in both border group and central group occurred by side-wall crystallization, but the salic magma became compositionally stratified, with upward concentration of alkalis and volatiles to produce a phonolitic upper facies which is preserved at the ENE end of the intrusion owing to subsequent axial tilting.

Keywords

mineralogygeochemistryalkali gabbrofoyaiteGardarGreenland
Type
Research Article
Information
Mineralogical Magazine , Volume 49 , Issue 354 , December 1985 , pp. 623 - 642
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1985

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References

Abbey, S. (1980) Geol. Surv. Can Paper 80-14.Google Scholar
Blaxland, A. B., van Breemen, O., Emeleus, C. H., and Anderson, J. G. (1978) Bull. geol. Soc. Am. 89, 231-44.2.0.CO;2>CrossRefGoogle Scholar
Blundell, D. J. (1978) J. geol. Soc. London, 135, 545-54.CrossRefGoogle Scholar
Bridgwater, D. (1967) Can. J. Earth Sci. 4, 995-1014.CrossRefGoogle Scholar
Buddington, A. F., and Lindsley, D. H. (1964) J. Petrol. 5, 310-57.CrossRefGoogle Scholar
Carmichael, I. S. E. (1967) Contrib. Mineral. Petrol. 14, 36–64.CrossRefGoogle Scholar
Chambers, A. D. (1976) The petrology and geochemistry of the North Qôroq Centre, Igaliko Complex, South Greenland. Unpubl. Ph.D. thesis, Univ. of Durham.Google Scholar
Emeleus, C. H., and Upton, B. G. J. (1976) In Geology of Greenland (Escher, A., and Watt, W. S., eds.). Copenhagen: The Geological Survey of Greenland, 153-81.Google Scholar
Gill, R. C. O. (1972) The geochemistry of the Grønnedal-Ika alkaline complex, South Greenland. Unpubl. Ph.D. thesis, Univ. of Durham.Google Scholar
Jones, A. P. (1980) The Petrology and structure of the Motzfeldt Centre, Igaliko, South Greenland. Unpubl. Ph.D. thesis, Univ. of Durham.Google Scholar
Jones, A. P. (1984) Mineral. Mag. 48, 1-12.CrossRefGoogle Scholar
Larsen, L. M. (1976) J. Petrol. 17, 258-90.CrossRefGoogle Scholar
Leake, B. E. (1978) Mineral. Mag. 42, 533-63.CrossRefGoogle Scholar
Norrish, K., and Hutton, J. T. (1969) Geochim. Cosmo-chim. Acta, 33, 431-53.CrossRefGoogle Scholar
Parsons, I. (1979) J. Petrol. 20, 653-94.CrossRefGoogle Scholar
Patchett, P. J., Hutchinson, J., Blaxland, A. B., and Upton, B. G. J. (1976) Bull. geol. Soc. Denmark, 25, 79–84.Google Scholar
Powell, M. (1978) Lithos, 11, 99-120.CrossRefGoogle Scholar
Powell, R., and Powell, M. (1977) Mineral. Mag. 41, 257-63.CrossRefGoogle Scholar
Rock, N. M. S., and Leake, B. E. (1984) Mineral. Mag. 48, 211-27.CrossRefGoogle Scholar
Spencer, K. J., and Lindsley, D. H. (1981) Am. Mineral. 66, 1189-201.Google Scholar
Stephenson, D. (1972) Lithos, 5, 187-201.CrossRefGoogle Scholar
Stephenson, D. (1974) Ibid. 7, 35-41.Google Scholar
Stephenson, D. (1976) Bull. Grønlands geol. Unders. 118, 55 pp.Google Scholar
Stephenson, D. and Upton, B. G. J. (1982) Mineral. Mag. 46, 283–300.CrossRefGoogle Scholar
Stormer, J. C. Jr. (1983) Am. Mineral. 68, 586-94.Google Scholar
Sun, S. S. (1980) Phil. Trans. R. Soc. Lond. A297, 409-45.Google Scholar
Sweatman, T. R., and Long, J. V. P. (1969) J. Petrol. 10, 332-79.CrossRefGoogle Scholar
Thirlwall, M. F. (1979) The petrochemistry of the British Old Red Sandstone Province. Unpubl. Ph.D. thesis, Univ. of Edinburgh.Google Scholar
Upton, B. G. J. (1962) Bull. Grønlands geol. Unders. 34 (also Meddr. Grønland, 169, 8) 60 pp.Google Scholar
Upton, B. G. J. (1964a) Ibid. 8 (also Meddr. Grønland, 169, 2) 1-47.Google Scholar
Upton, B. G. J. (1964b) Ibid. 8 (also Meddr. Grønland, 169, 2) 49-180.Google Scholar
Upton, B. G. J. (1974) In The Alkaline Rocks (Sorensen, H., ed.) John Wiley, New York, 221-38.Google Scholar
Upton, B. G. J. and Blundell, D. J. (1978) In Petrology and Geo chemistry of Continental Rifts (Neumann, E. R. and Ramberg, I. B., eds.) Reidel, Dordrecht, 163-72.CrossRefGoogle Scholar
Upton, B. G. J. and Thomas, J. E. (1980) J. Petrol. 21, 167-98.CrossRefGoogle Scholar
van Breemen, O., and Upton, B. G. J. (1972) Bull. geol. Soc. Am. 83, 3381-90.CrossRefGoogle Scholar
van Breemen, O., Aftalion, M., and Allaart, J. H. (1974) Ibid. 85, 403-12.Google Scholar
Walsh, J. N., Buckley, F., and Barker, J. (1981) Chem. Geol. 33, 141-53.CrossRefGoogle Scholar
Wörner, G., and Schminke, H.-U. 9 (1984). J. Petrol. 25, 805-35.CrossRefGoogle Scholar