Textural evolution of the rapakivi granites, South Greenland; Sr, O and H isotopic investigations

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Authors:Dempster, T. J.; Hutton, D. H. W.; Harrison, T. N.; Brown, P. E.; Jenkin, G. R. T.
Author Affiliations:Primary:
University of Glasgow, Department of Geology and Applied Geology, Glasgow, United Kingdom
University of Durham, United Kingdom
University of Aberdeen, United Kingdom
Scottish Universities Research and Reactor Centre, United Kingdom
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 107(4), p.459-471. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1991
Note:In English. 57 refs.; illus. incl. 1 plate, 3 tables, geol. sketch map
Summary:The development of rapakivi texture in feldspars from the Ketilidian granitic rocks of S Greenland was investigated, using Sr, O and H isotopes. A low-T signature is found in the Sr and O data which seemingly contradicts some textural features that point to a magmatic origin for the plagioclase mantles around the K- feldspar ovoids. An origin for these mantles involving exsolution from an original alkali feldspar solid solution is proposed, which involves growth of mantles over a range of conditions determined by the mobility of the exsolving sodic feldspar. This mobility may be enhanced at high T in the presence of melts or increased fluid P and at lower T by the processes responsible for the transformation of K-feldspar to microcline. Rapakivi granites with both white and dark green feldspar occur in S Greenland but show no major isotopic differences, although the dark alkali feldspars contain significantly more fluid. Equivalent fluids in the white alkali feldspars may have escaped during plagioclase exsolution. [Authors' abstract] [P.Br.]
Subjects:Alkali feldspar; Alkali metals; Alkaline earth metals; C-13/C-12; Carbon; Crystallization; D/H; Exsolution; Facies; Feldspar group; Framework silicates; Granites; Granulite facies; Hydrogen; Igneous rocks; Isotopes; Ketilidian Orogeny; Mesoproterozoic; Metals; Microcline; O-18/O-16; Oxygen; Paleoproterozoic; Perthite; Petrography; Plagioclase; Plutonic rocks; Precambrian; Proterozoic; Radioactive isotopes; Rapakivi; Rb-87/Sr-86; Relict materials; Rubidium; Silicates; Sr-87/Sr-86; Stable isotopes; Strontium; Textures; Upper Precambrian; Arctic region; Greenland; South Greenland; Ilua Fjord; Kap Farvel; Qernertoq
Abstract Numbers:92M/0611
Record ID:1993024864
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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