OH-bearing planar defects in olivine produced by the breakdown of Ti-rich humite minerals from Dabie Shan (China)

Jörg Hermann*, John D. Fitz Gerald, Nadia Malaspina, Andrew J. Berry, Marco Scambelluri

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    51 Citations (Scopus)

    Abstract

    The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies conditions in garnet-pyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxyl-stretching region. Two intense peaks were observed at 3,564 and 3,394 cm-1, identical in energy to peaks in Ti-clinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable in hotter parts of the oceanic mantle such as where basaltic magmas are generated.

    Original languageEnglish
    Pages (from-to)417-428
    Number of pages12
    JournalContributions to Mineralogy and Petrology
    Volume153
    Issue number4
    DOIs
    Publication statusPublished - Apr 2007

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