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Article Dans Une Revue Chemical Geology Année : 2019

A trace of recycled continental crust in the Réunion hotspot

Résumé

Réunion Island is the present surface expression of a major mantle plume whose homogeneity and isotopic signature, near the convergence point of many hotspot isotopic arrays, have long puzzled geochemists. This signature could, in part, reflect oversampling of the most recent (<0.53 Ma) Piton de la Fournaise volcano. To resolve this issue, we studied the older Piton des Neiges volcano and made a synthesis of the Sr-Nd-Pb isotope compositions of lavas produced during the early stage of La Réunion and contemporaneously at Mauritius, the second youngest island of the hotspot track. New samples from Piton des Neiges have 87Sr/86Sr from 0.70429 to 0.70441, 143Nd/144Nd from 0.51282 to 0.51290, 206Pb/204Pb from 18.765 to 19.004, 207Pb/204Pb from 15.558 to 15.605 and 208Pb/204Pb from 38.850 to 39.082. On a SrNd isotope plot, the extended isotope field defined by the Réunion and Mauritius volcanoes overlaps with the OIB field of the Society islands, where an EM-2 signature has been recognized. Réunion also has higher 207Pb/204Pb and 208Pb/204Pb ratios for a given 206Pb/204Pb than expected from a binary mixing between depleted and enriched mantle components. Thus, the overall Sr-Nd-Pb isotope variations shown by Réunion and Mauritius volcanoes require a third source component. In addition to the already known depleted and enriched mantle components, the third component involved in the mixing is interpreted as reflecting a small contribution (≤ 8%) of Seychelles/Madagascar-like continental crust, which is incorporated into the plume before it rises into the depleted mantle. This new model challenges the proposed existence of a hidden continent below the island of Mauritius, by suggesting that the continental component is located in the asthenosphere.

Domaines

Géochimie
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Dates et versions

hal-02163315 , version 1 (19-08-2019)

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François Nauret, Vincent Famin, Ivan Vlastélic, Abdelmouhcine Gannoun. A trace of recycled continental crust in the Réunion hotspot. Chemical Geology, 2019, 524, pp.67-76. ⟨10.1016/j.chemgeo.2019.06.009⟩. ⟨hal-02163315⟩
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