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The rapakivi granites of S Greenland—crustal melting in response to extensional tectonics and magmatic underplating

Published online by Cambridge University Press:  03 November 2011

P. E. Brown ,
T. J. Dempster ,
T. N. Harrison  and
D. H. W. Hutton
P. E. Brown
Affiliation:
P. E. Brown, Department of Geology, University of St Andrews, St Andrews, KY16 9ST, Scotland
T. J. Dempster
Affiliation:
T. J. Dempster, Department of Geology and Applied Geology, University of Glasgow, Glasgow G12 8QQ, Scotland
T. N. Harrison
Affiliation:
T. N. Harrison, c/o Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, AB9 2UE, Scotland
D. H. W. Hutton
Affiliation:
D. H. W. Hutton, Department of Earth Sciences, University of Durham, South Road, Durham, DH1 3LA, England
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Abstract

Early Proterozoic rapakivi intrusions in S Greenland occur as thick sheets which have ramp–flat geometry and were intruded along the median planes of active ductile extensional shear zones. These shear zones and their intrusions were linked via transfer zones in a major three-dimensional framework. At high structural levels (c. 6 km) the rapakivi intrusions developed thermal aureoles which overprint the regional assemblages, whereas at deeper levels in the regional structure they are contemporaneous with regional metamorphism. Thermobarometry on the regional and contact assemblages indicates low pressure granulite facies conditions (200–400 MPa, 650°-800°C) suggesting very high thermal gradients. The rapakivi suite and associated norites have low initial 87Sr/86Sr together with positive εNd values, indicating the involvement of predominantly young crust and/or mantle component in the generation of the igneous suite. It is considered that the voluminous norites are closely related to the mafic melts which underplated the juvenile crust to trigger the generation of the monzonitic rapakivi suite. Taken together, the data are consistent with a model of Proterozoic lithospheric extension, thinning of relatively juvenile continental crust and compression of mantle isotherms, resulting in high crustal heat flow, mafic underplating, and crustal melting with emplacement of magmas along a linked network of extensional shear zones.

Keywords

Bimodal magmatismextensiongranulites
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 83 , Issue 1-2: Second Hutton Symposium: The Origin of Granites and Related Rocks , 1992 , pp. 173 - 178
Copyright
Copyright © Royal Society of Edinburgh 1992

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References

Allart, J. H. 1976. The Ketilidian mobile belt in South Greenland. In Escher, A. & Watt, W. S. (eds) Geology of Greenland, 121–51. GRONL GEOL UNDERS COPENHAGEN.Google Scholar
Bridgwater, D., Sutton, J. & Watterson, J. 1974. Crustal downfolding associated with igneous activity. TECTONOPHYSICS 21, 57–77.CrossRefGoogle Scholar
Collins, W. J., Beams, S. D., White, A. J. R. & Chappell, B. W. 1982. Nature and origin of A-type granites with particular reference to south-eastern Australia. CONTRIB MINERAL PETROL 80, 189–200.CrossRefGoogle Scholar
Creaser, R. A., Price, R. C. & Wormald, R. J. 1991. A-type granites revisted: Assessment of a residual-source model. GEOLOGY 19, 163–6.2.3.CO;2>CrossRefGoogle Scholar
Dawes, P. R. 1970. The plutonic history of the Tasiussaq area, South Greenland, with special reference to a high-grade gneiss complex. BULL GRONL GEOL UNDERS 88.Google Scholar
Dempster, P. J., Hutton, D. H. W., Harrison, T. N., Brown, P. E. & Jenkin, G. R. T. 1991a. Textural evolution of rapakivi granites, south Greenland—Sr, O and H isotopic investigations. CONTRIB MINERAL PETROL 107, 459–71.CrossRefGoogle Scholar
Dempster, T. J., Harrison, T. N., Brown, P. E. & Hutton, D. H. W. 1991b. Low-pressure granulites from the Ketilidian mobile belt of south Greenland. J PETROL 32, 979–1004.CrossRefGoogle Scholar
Emslie, R. F. 1991. Granitoids of rapakivi granite—anorthosite and related associations. PRECAMBRIAN RES 51, 173–92.CrossRefGoogle Scholar
Finch, A. A., Reavy, R. J., Harrison, T. N. & Brown, P. E. 1990. Rapakivi granites, south Greenland: hydrothermal alteration of igneous layering. J GEOL SOC 147, 739–42.CrossRefGoogle Scholar
Gulson, B. L. & Krogh, T. E. 1975. Evidence of multiple intrusion, possible resetting of U-Pb ages, and new crystallisation of zircons in the post-tectonic intrusions (Rapakivi granites) and gneisses from south Greenland. GEOCHIM COSMOCHIM ACTA 39, 65–82.CrossRefGoogle Scholar
Harrison, T. N., Parsons, I. & Brown, P. E. 1990a. Fayalite-bearing rapakivi granites from the Prins Christian Sund pluton, south Greenland. MINERAL MAG 54, 57–64.CrossRefGoogle Scholar
Harrison, T. N., Reavy, R. J., Finch, A. A. & Brown, P. E. 1990b. Co-existing mafic and felsic magmas in the early Proterozoic rapakivi granite suite of Southern Greenland. BULL GEOL SOC DENMARK 38, 53–8.CrossRefGoogle Scholar
Holland, T. J. B. & Powell, R. 1990. An enlarged and updated internally consistent thermodynamic data set with uncertainties and correlations: the system K2O–Na2O–CaO–MgO–MnO–FeO–Fe2O3–Al2O3–TiO2–SiO2–C–H2–O2. J METAM GEOL 8, 89–124.CrossRefGoogle Scholar
Huppert, H. E. & Sparks, R. S. 1988. The generation of granitic magmas by intrusion of basalt into continental crust. J PETROL 29, 599–624.CrossRefGoogle Scholar
Hutton, D. H. W. 1988. Granite emplacement mechanisms and tectonic controls: inferences from deformation studies. TRANS R SOC EDINBURGH EARTH SCI 79, 245–55.Google Scholar
Hutton, D. H. W., Dempster, T. J., Brown, P. E. & Becker, S. M. 1990. A new mechanism of granite emplacement: rapakivi intrusions in active extensional shear zones. NATURE 343, 452–4.CrossRefGoogle Scholar
Johannes, W. & Holtz, F. 1990. Formation and composition of H2O-undersaturated granitic melts. In Ashworth, J. R. & Brown, M. (eds) High temperature metamorphism and crustal anatexis, 87–104. London: Unwin Hyman.CrossRefGoogle Scholar
Nekvasil, H. 1988. Calculated effect of anorthite component on the crystallisation paths of H2O-undersaturated haplogranitic melts. AM MINERAL 73, 966–81.Google Scholar
O'Connor, J. T. 1965. A classification for quartz-rich igneous rocks based on feldspar ratios. GEOL SURV AM Prof Pap 525–B, 79–84.Google Scholar
Patchett, P. J. & Bridgwater, D. 1984. Origin of continental crust of 1–9–1·7Ga age defined by Nd isotopes in the Ketilidian terrain of South Greenland. CONTRIB MINERAL PETROL 87, 311–8.CrossRefGoogle Scholar
Pearce, J. A., Harris, N. B. W. & Tindle, A. G. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J PETROL 25, 956–83.CrossRefGoogle Scholar
Powell, R. & Holland, T. J. S. 1988. An internally consistent thermodynamic data set with uncertainties and correlations: 3 Applications to Geobarometry, worked examples and a computer programme. J METAM GEOL 6, 173–204.CrossRefGoogle Scholar
Watterson, J. 1978. Proterozoic intraplate deformation in the light of South-east Asian neotectonics. NATURE 273, 636–40.CrossRefGoogle Scholar
Whalen, J. B., Currie, K. L. & Chappell, B. W. 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. CONTRIB MINERAL PETROL 95, 407–19.CrossRefGoogle Scholar
Windley, B. F. 1991. Early Proterozoic collision tectonics, and rapakivi granites in an extensional thrust-thickened crust: the Ketilidian orogen, South Greenland. TECTONOPHYSICS 195, 1–10.CrossRefGoogle Scholar