A possible link between gabbros bearing high temperature iddingsite alteration and huge pegmatoid intrusions: The Society Islands, French Polynesia
|Author(s)||Clement Jean-Philippe1, Caroff Martial1, Dudoignon Patrick2, Launeau Patrick3, Bohn Marcel4, Cotten Joseph1, Blais Sylvain5, Guille Gérard6|
|Affiliation(s)||1 : Univ Bretagne Occidentale, UMR 6538, IUEM, F-29238 Brest 3, France.
2 : Univ Poitiers, Ecole Super Ingn Poitiers, UMR 6532, HydrASA, F-86022 Poitiers, France.
3 : Univ Nantes, UFR Sci & Tech, Planetol & Geodynam UMR 6112, F-44072 Nantes, France.
4 : IFREMER, Ctr Brest, Domaines Ocean UMR 6538, Dept Geosci Marines, F-29280 Plouzane, France.
5 : Univ Rennes 1, Geosci Rennes UMR 6118, F-35042 Rennes, France.
6 : CEA, Grp Teledetect & Risques Sismiques, DASE, F-91680 Bruyeres Le Chatel, France.
|Source||Lithos (0024-4937) (Elsevier), 2007-07 , Vol. 96 , N. 3-4 , P. 524-542|
|WOS© Times Cited||10|
|Keyword(s)||Society Islands, French Polynesia, Pegmatoid, Vapor differentiation, Olivine, Gabbros|
|Abstract||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.|