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Provedor de dados:  ArchiMer
País:  France
Título:  A possible link between gabbros bearing high temperature iddingsite alteration and huge pegmatoid intrusions: The Society Islands, French Polynesia
Autores:  Clement, Jean-philippe
Caroff, Martial
Dudoignon, Patrick
Launeau, Patrick
Bohn, Marcel
Cotten, Joseph
Blais, Sylvain
Guille, Gérard
Data:  2007-07
Ano:  2007
Palavras-chave:  Society Islands
French Polynesia
Vapor differentiation
Resumo:  This paper reports new field observations and new petrological, textural and geochemical data on two gabbroic intrusions and one pegmatoid dyke from the French Polynesian islands Maupiti and Bora Bora, respectively. Olivine crystals from the Faataufi and Barque de Hiro gabbros (Maupiti) include High Temperature Iddingsite (HTI), exhibiting three distinct morphological facies. Chemical and crystallographical data performed by electron microprobe, scanning microscope, X-ray diffractometry and Near InfraRed spectroscopy show that HTI results from modifications of olivine structure through intense hydroxylation and Fe-oxidation. The HTI-free 120 m-wide Cloche de Hiro dyke (Bora Bora) exhibits a textural zonation from heterogranular/intergranular gabbro (peripheral part) to typical pegmatoid (inner area). We propose a textural tetrahedral classificatory diagram which can be used to clearly distinguish the textural characteristics of the pegmatoids from those of the other coarse-grained samples. Through comparison with a lava flow containing vesicle-rich segregation sheets, we suggest that the Cloche de Hiro dyke may correspond to a huge segregation structure derived from a Maupiti-type HTI-bearing gabbro through a vapor-differentiation process. Both intrusions might be considered as representative of two superposed levels in a vertically arranged magmatic complex. In this view, the Maupiti gabbroic bodies would represent the lower part of the postulated system. Under high oxygen fugacity, olivine crystals would have undergone important modifications of their structure, leading to HTI. The huge Bora Bora pegmatoid dyke would be the upper part of the complex. After expulsion from the HTI-bearing gabbroic solidification zone by build-up of gas pressure, vesicle-rich residual melt would have gathered into a shallow level and crystallized there as a pegmatoid body. (C) 2006 Elsevier B.V All rights reserved.
Tipo:  Text
Idioma:  Inglês

Editor:  Elsevier
Formato:  application/pdf
Fonte:  Lithos (0024-4937) (Elsevier), 2007-07 , Vol. 96 , N. 3-4 , P. 524-542
Direitos:  2006 Elsevier B.V. All rights reserved

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