Extremely low structural hydroxyl contents in upper mantle xenoliths from the Nógrád-Gömör Volcanic Field (northern Pannonian Basin): Geodynamic implications and the role of post-eruptive re-equilibration - Université de Lille Accéder directement au contenu
Article Dans Une Revue Chemical Geology Année : 2019

Extremely low structural hydroxyl contents in upper mantle xenoliths from the Nógrád-Gömör Volcanic Field (northern Pannonian Basin): Geodynamic implications and the role of post-eruptive re-equilibration

Levente Patkó
  • Fonction : Auteur
Nóra Liptai
  • Fonction : Auteur
István János Kovács
  • Fonction : Auteur
László El Aradi
  • Fonction : Auteur
Qun-Ke Xia
  • Fonction : Auteur
Judith Mihály
  • Fonction : Auteur
Suzanne Y. O'Reilly
  • Fonction : Auteur
William L. Griffin
  • Fonction : Auteur
Viktor Wesztergom
  • Fonction : Auteur
Csaba Szabó
  • Fonction : Auteur

Résumé

The structural hydroxyl content of the nominally anhydrous minerals (olivine and pyroxenes) in the upper mantle is among the important attributes that influence the physical and chemical features of the upper mantle. In this study, we provide detailed Fourier-transform infrared (FTIR) data on 63 petrographically and geochemically well-defined upper mantle xenoliths from the Nograd-Gomor Volcanic Field (Pannonian Basin, Central Europe). These xenoliths show extremely low average structural hydroxyl contents (similar to 0, 31 and 185 ppm for olivine, orthopyroxene and clinopyroxene, respectively) compared to values reported regionally and worldwide. The studied xenoliths have anomalous types of FTIR spectra and high structural hydroxyl ratios between clinopyroxenes and orthopyroxenes (an average of similar to 8). Furthermore, there is usually no correlation between the structural hydroxyl content and other physical or chemical properties of the xenoliths. These specific FTIR characteristics suggest that the Nograd-Gomor upper mantle xenoliths were exposed to significant modification of their structural hydroxyl contents, which may be linked to pre- and post-eruptive processes. Decompression during extension leads to lower 'water' activity, which is most likely to have played a key role. However, pre-eruptive mantle metasomatism with an agent having low water activity cannot be excluded either. The post-eruptive cooling can be significant as well, as suggested by the higher structural hydroxyl content in xenoliths hosted in more rapidly cooled volcanic facies (i.e. pyroclastics). Our study reveals how FTIR characteristics may evolve in continental rift settings in young extensional basins. Furthermore, novel applications of our study are the diagnostic features that indicate significant changes in structural hydroxyl properties. This contributes to distinguishing low structural hydroxyl contents linked to the pre-eruptive (i.e., low structural hydroxyl content in pyroxenes, anomalous partitioning and anomalous band characteristic in pyroxenes) or the post-eruptive (completely 'dry' olivines) periods.
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hal-02313678 , version 1 (11-10-2019)

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Levente Patkó, Nóra Liptai, István János Kovács, László El Aradi, Qun-Ke Xia, et al.. Extremely low structural hydroxyl contents in upper mantle xenoliths from the Nógrád-Gömör Volcanic Field (northern Pannonian Basin): Geodynamic implications and the role of post-eruptive re-equilibration. Chemical Geology, 2019, Chemical Geology, 507, pp.23-41. ⟨10.1016/j.chemgeo.2018.12.017⟩. ⟨hal-02313678⟩
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