• Citer

Kerguelen Archipelago revisited: geochemical and isotopic study of the Southeast Province lavas

par Weis, Dominique ;Gautier, Isabelle;Frey, Frederic A;Leyrit, Hervé
Référence Earth and planetary science letters, 118, 1-4, page (101-119)
Publication Publié, 1993

Article révisé par les pairs

• Accès en ligne
• Détails
• Contenu
• Statistiques

Résumé :

In order to constrain an isotopically extreme mantle component involved in the genesis of oceanic basalts, we studied some of the youngest lavas of the Kerguelen Archipelago. According to the model developed by Gautier et al. [1], these young lavas were derived from the Kerguelen mantle plume, with little, if any, depleted MORB component. The alkaline lavas in the Southeast Province of the Kerguelen Archipelago correspond to two main volcanic phases: (a) a 20-22 Ma old lower Miocene series with basalts and trachytes belonging to a mildly alkaline series comparable to the mildly alkaline series of Gautier et al. [1] and (b) a 6.6-10.2 Ma old [2] upper Miocene series with basanites, tephri-phonolites and phonolites, forming a highly alkaline series. The lower Miocene lavas have ε{lunate}Nd, 87Sr/86Sr and Pb isotopic ratios overlapping with those of Kerguelen transitional and mildly alkaline series, i.e. ε{lunate}Nd from +2.2 to -0.6 and 87Sr/86Sr between 0.70493 and 0.70522. The upper Miocene lavas have higher 87Sr/86Sr ratios (> 0.7054) and lower ε{lunate}Nd ( ≪ 0), i.e. comparable to the highly alkaline series of Gautier et al. [1]. In contrast, compared to other lavas from the Kerguelen Archipelago, the upper Miocene lavas have distinctly less radiogenic 206Pb/204Pb ratios. They plot to the left of the Indian OIB field in PbPb diagrams, i.e. in a direction opposite to that expected for contamination with sediment or young continental crust. In both series, the evolved lavas and associated basalts/basanites overlap in isotopic ratios, although incompatible element abundance ratios in the evolved lavas were modified by fractionation of amphibole, FeTi oxides, apatite and sphene. We propose that the isotopic characteristics of the upper Miocene lavas correspond to the pure Kerguelen plume signature, which is: 87Sr/86Sr = 0.7054-0.7058, ε{lunate}Nd = -0.2 to -2.9, 206Pb/204Pb = 18.06-18.27, 207Pb/204Pb = 15.54-15.58 and 208Pb/204Pb = 38.68-39.16. The Kerguelen plume therefore has an intermediate isotopic composition and corresponds neither to the EM I nor the EM II component [3]. A continuum between EM I and EM II is expected for mantle contaminated by recycled continental crust or continent-derived material. © 1993.