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
Other:
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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