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Journal of Petrology Advance Access originally published online on May 20, 2005
Journal of Petrology 2005 46(9):1925-1962; doi:10.1093/petrology/egi043
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© The Author 2005. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oupjournals.org

Origin of Exceptionally Abundant Phonolites on Ua Pou Island (Marquesas, French Polynesia): Partial Melting of Basanites Followed by Crustal Contamination

C. LEGENDRE1,*, R. C. MAURY1, M. CAROFF1, H. GUILLOU2, J. COTTEN1, C. CHAUVEL3, C. BOLLINGER4, C. HÉMOND4, G. GUILLE5, S. BLAIS6, P. ROSSI7 and D. SAVANIER7

1 UMR 6538, IUEM, UNIVERSITÉ DE BRETAGNE OCCIDENTALE, 6 AVENUE LE GORGEU, CS 93837, 29238 BREST CEDEX 3, FRANCE
2 LSCE/CEA–CNRS UMR 1572, DOMAINE DU CNRS, 12 AVENUE DE LA TERRASSE, 91118 GIF-SUR-YVETTE, FRANCE
3 LGCA, 1381 RUE DE LA PISCINE, BP 53, 38000 GRENOBLE, FRANCE
4 UMR 6538, IUEM, UNIVERSITÉ DE BRETAGNE OCCIDENTALE, PLACE N. COPERNIC, 29280 PLOUZANÉ, FRANCE
5 CEA/LDG, BP 12, 91680 BRUYÈRES-LE-CHATEL, FRANCE
6 LABORATOIRE DE PÉTROLOGIE CRISTALLINE, GÉOSCIENCES RENNES, UMR 6118, UNIVERSITÉ DE RENNES 1, 35042 RENNES, FRANCE
7 BRGM, BP 6009, 45060 ORLÉANS CEDEX 2, FRANCE

RECEIVED JULY 30, 2004; ACCEPTED MARCH 21, 2005

On the basis of the first systematic mapping of Ua Pou, long known for its exceptionally abundant phonolites, we estimate that these rocks cover 65% of the surface of the island whereas mafic lavas cover 27% and intermediate ones 8%. The silica-undersaturated suite was erupted in a restricted time span (2·9–2·35 Myr), following the emplacement of tholeiites derived from a young HIMU-type source at c. 4 Ma. Primitive basanites, derived from a heterogeneous mantle source with a dominant EM II + HIMU signature, represent likely parental magmas. The series is characterized by a Daly gap defined by a lack of phonotephrites. We consider that the most likely model for the origin of evolved lavas is partial melting at depth of primitive basanites, leaving an amphibole-rich residuum and producing tephriphonolitic magmas. These tephriphonolitic magmas may have evolved by closed-system fractional crystallization towards Group A phonolites. Three other groups of phonolites could have been derived from tephriphonolitic magmas by open-system fractional crystallization processes, characterized respectively by seawater contamination (Group B), assimilation of nepheline syenite-type materials (Group C) and extreme fractionation coupled with assimilation of the underlying oceanic crust (Group D). The prominence of evolved lavas is a consequence of their origin from partial melting of mafic precursors followed by crustal contamination.

KEY WORDS: Marquesas; French Polynesia; phonolite; partial melting; contamination

* Corresponding author. Present address: Laboratoire de Planétologie et de Géodynamique UMR-6112, Université de Nantes, 2 rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France. Telephone: (33) 2 51 12 52 82. Fax: (33) 2 51 12 52 68. E-mail: christelle.legendre{at}univ-nantes.fr


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