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Genesis of orbicular granitic rocks from Ploumanac'h plutonic complex (Brittany, France); petrographical, mineralogical and geochemical constraints

Sylvie Decitre, Dominique Gasquet and Christian Marignac
Genesis of orbicular granitic rocks from Ploumanac'h plutonic complex (Brittany, France); petrographical, mineralogical and geochemical constraints
European Journal of Mineralogy (August 2002) 14 (4): 715-731

Abstract

The studied orbicular body is found in the evolved high-K calc-alkaline La Clarte granite in the Ploumanac'h complex. The orbicules are composed of plumose K-feldspar around various nucleus. Reconstruction of the composition of the "orbicular magmas" and their crystallisation conditions indicate that the following conditions are required for the genesis of the orbicules: (1) a small (600 m (super 3) ) insulated pocket of heated magma generated by the (re)melting of the cumulate Traouieros granite; (2) a magma composition enriched in K-feldspar component which allows for a significant production of K-feldspar prior to the attainment of the Q-Ab-Or minimum and the final crystallisation of the magma; (3) a high confining pressure leads to a high crystallisation ratio prior to the exsolution of the water phase, which facilitates the development of radiated shells and (4) the existence in the melt of numerous "cold" germs (K-feldspar phenocrysts, with also hornblendites, microdiorites and granites) that act to nucleate the crystallisation of the shells. The orbicules represent, thus, a "stockscheider" structure with endless "cold" walls.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 14
Serial Issue: 4
Title: Genesis of orbicular granitic rocks from Ploumanac'h plutonic complex (Brittany, France); petrographical, mineralogical and geochemical constraints
Affiliation: CNRS-CRPG, Vandoeuvre-les-Nancy, France
Pages: 715-731
Published: 200208
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 41
Accession Number: 2002-064883
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch map
N42°30'00" - N51°00'00", W05°00'00" - E08°30'00"
Secondary Affiliation: INPL, FRA, France
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200220
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