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Journal of Petrology Advance Access published online on July 8, 2005
Journal of Petrology, doi:10.1093/petrology/egi055
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© The Author 2005. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oupjournals.org
Received January 6, 2004
Accepted April 20, 2005

Article

Petrogenesis of Coarse-grained Intrusives from Tahiti Nui and Raiatea (Society Islands, French Polynesia)

CAROLE CORDIER 1*, JEAN-PHILIPPE CLÉMENT 2, MARTIAL CAROFF 1, CHRISTOPHE HÉMOND 1, SYLVAIN BLAIS 3, JOSEPH COTTEN 1, CLAIRE BOLLINGER 1, PATRICK LAUNEAU 4, and GÉRARD GUILLE 5

1 UMR6538 «DOMAINES OCÉANIQUES», IUEM, UFR DES SCIENCES ET TECHNIQUES, UNIVERSITÉ DE BRETAGNE OCCIDENTALE, 6 AVENUE LE GORGEU, C.S. 93837, 29238 BREST CEDEX, FRANCE
2 UMR6538 «DOMAINES OCÉANIQUES», IUEM, UFR DES SCIENCES ET TECHNIQUES, UNIVERSITÉ DE BRETAGNE OCCIDENTALE, 6 AVENUE LE GORGEU, C.S. 93837, 29238 BREST CEDEX, FRANCE; Present address: UMR 5025 ‘Laboratoire de Géodynamique des Chaînes Alpines’, Université Grenoble 1--Joseph Fourier, Maison des Géosciences, 1381 rue de la Piscine, BP 53, 38041 Grenoble Cedex 9, France
3 LABORATOIRE DE PÉTROLOGIE CRISTALLINE, GÉOSCIENCES RENNES, CNRS UMR 6118, UNIVERSITÉ DE RENNES I, 35042 RENNES CEDEX, FRANCE
4 UMR 6112 «PLANÉTOLOGIE ET GÉODYNAMIQUE», UFR DES SCIENCES ET TECHNIQUES, UNIVERSITÉ DE NANTES, 2 RUE DE LA HOUSSINIÈRE, 44072 NANTES, FRANCE
5 CEA/LDG LABORATOIRE DE DÉTECTION ET DE GÉOPHYSIQUE, BP 12, 91680 BRUYÈRES-LE-CHÂTEL, FRANCE

* To whom correspondence should be addressed.
CAROLE CORDIER, E-mail: carole.cordier{at}sdt.univ-brest.fr


  Abstract

This study is based on a set of coarse-grained igneous rocks collected from two zoned plutons located in the central part of Tahiti Nui and Raiatea. The Ahititera pluton (central depression of Tahiti Nui) comprises a great diversity of rocks, ranging from ultrabasic to felsic in composition. It shows a concentric zonation with nepheline-free rocks in its periphery and nepheline-bearing rocks in its central part. The Faaroa pluton (central depression of Raiatea) is entirely mafic and includes only gabbros and theralites. The two plutons have variable Nd-Sr isotopic signatures, especially the Ahititera rocks, which are subdivided into three groups based on their mineralogy, geochemistry and isotope composition. The isotopic variability probably reflects local heterogeneities in the Society mantle plume. Petrographic and isotopic data have been used to define two magmatic suites in Ahititera, identifiable from their degree of Si undersaturation. The evolution of the mildly Si-undersaturated suite is controlled by simple fractional crystallization, whereas the strongly Si-undersaturated suite requires additional H2O influx. The third isotopic group includes only theralites. The rare earth element (REE) compositions of the mafic rocks from both plutons do not correlate with their isotopic signature. The REE patterns of the most Si-undersaturated rocks are systematically characterized by steeper slopes. Such features are also observed in lavas from seamounts located within the present-day hotspot area. It appears that REE concentrations in Society lavas and intrusives are probably mainly governed by variable degrees of partial melting of a garnet-free mantle source and are independent of their isotopic signature.

Keywords: cumulates; fractional crystallization; partial melting; French Polynesia; plutonic rocks; Society Islands; Tahiti; Raiatea.
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