Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by DECITRE, S. Articles by MARIGNAC, C. Search for Related Content GeoRef GeoRef Citation

Genesis of orbicular granitic rocks from the Ploumanac'h Plutonic Complex (Brittany, France)

¹ CRPG-CNRS, BP 20, F-54501 Vandoeuvre-lès-Nancy Cedex, France
² ENSG-INPL, BP 40, F-54501 Vandoeuvre-lès-Nancy Cedex, France
³ EMN-INPL, F-54042 Nancy Cedex, France

^* Corresponding author, e-mail: gasquet{at}crpg.cnrs-nancy.fr

The studied orbicular body is found in the evolved high-K calc-alkaline La Clarté 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 m³) insulated pocket of heated magma generated by the (re)melting of the cumulate Traouiéros 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.

Key-words: orbicular granites, plumose feldspars, high-K calc-alkaline granite, Ploumanac'h.

This article has been cited by other articles:

				A. LINDH and H. NASSTROM Crystallization of orbicular rocks exemplified by the Slattemossa occurrence, southeastern Sweden Geological Magazine, September 1, 2006; 143(5): 713 - 722. [Abstract] [Full Text] [PDF]

				S. Frindt, S. Frindt, and I. Haapala Anorogenic Gross Spitzkoppe granite stock in central western Namibia: Part II. Structures and textures indicating crystallization from undercooled melt American Mineralogist, May 1, 2004; 89(5-6): 857 - 866. [Abstract] [Full Text] [PDF]