The nodular granite of Castanheira, north central Portugal; origin of the nodules and evidence for diapiric mobilization of granite

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Authors:Reavy, R. J.; Hutton, D. H. W.; Finch, A. A.
Author Affiliations:Primary:
University of Oxford, Department of Earth Sciences, Oxford, United Kingdom
Other:
University of Durham, United Kingdom
University of Aberdeen, United Kingdom
Volume Title:Geological Magazine
Source:Geological Magazine, 130(2), p.145-153. Publisher: Cambridge University Press, London, United Kingdom. ISSN: 0016-7568
Publication Date:1993
Note:In English. 9 refs.; illus. incl. 2 tables, sect., geol. sketch maps
Summary:The pluton is a small (1000 x 600 m) body which contains a remarkable abundance of granite-cored, biotite-rimmed nodules. These are interpreted as representing original bubbles in the uppermost volatile-rich zone of a granitic plutonic. Strong depletion in Rb and K in the host granite around the nodules suggests that the biotite is magmatic in origin. The nodules may have formed by reaction between chloroferrate (II) complexes in the vapour phase and silicate melt, possibly following condensation of the vapour phase to a small granitic core. Motion of the vapour bubble stabilized a gradient in chemical potential with respect to the host granite,giving rise to the nodules. Chemical, petrological and structural data suggest that the pluton was part of a larger body which was forcefully emplaced during synchronous transcurrent shearing. [C.H.D.]
Subjects:Diapirs; Emplacement; Genesis; Granites; Igneous rocks; Inclusions; Intrusions; Plutonic rocks; Plutons; Shear; Xenoliths; Europe; Iberian Peninsula; Portugal; Southern Europe; Castanheira Pluton; North-central Portugal
Abstract Numbers:93M/4777
Record ID:1993019894
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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