Structural state of K-feldspar in some Hercynian granites from Iberia; a review of data and controlling factors

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Authors:Neves, L. J. P. F.; Godinho, M. M.
Author Affiliations:Primary:
Universidade de Coimbra, Dipartamento de Ciencias da Terra, Portugal
Volume Title:Canadian Mineralogist
Source:The Canadian Mineralogist, Vol.37(Part 3), p.691-700. Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada. ISSN: 0008-4476
Publication Date:1999
Note:In English with French summary. 38 refs.; illus.
Summary:Several hundred concentrates of K-feldspar from the Hercynian granites and associated aplites and pegmatites of central Portugal were studied by XRD to assess their structural state and to make inferences about their petrogenesis. Their structural state was indicated by the diffraction pattern in the 2θ region 29-31° using CuKα radiation, the ordering index ΔSM and Al-Si distribution derived from cell parameters; a range of values were obtained, though aplites and pegmatites showed less variability. In the great majority of samples from the granites, > 80% of Al is in the T1 site of the K-feldspar. It is concluded that the cooling rate of the granite was the factor controlling the ordering process of these K-feldspars; rapid unroofing of the older granites enhanced the cooling rate, retarding ordering. [R.A.H.]
Sections:Crystal structure
Subsections:Specific structures: silicates
Subjects:Alkali feldspar; Feldspar group; Framework silicates; Granites; Igneous rocks; K-feldspar; Mineral composition; Orogeny; Paragenesis; Pegmatite; Plutonic rocks; Silicates; Thermal history; Variscan Orogeny; X-ray diffraction data; Europe; Iberian Massif; Iberian Peninsula; Portugal; Southern Europe
Abstract Numbers:00M/2461
Record ID:2000018381
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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