Testing and Applying Thermodynamic Models for the Melting of Mantle Peridotites

• Author / Creator

  Wang, Daoheng

• The covariance of increasing spinel Cr# and olivine Mg# (“the olivine-spinel mantle array” or “OSMA”) has been used as a sensitive indicator for the melting history of mantle peridotites. The basis for this model has been largely empirical thus far. In this study, the most recent THERMOCALC-based models are used to study the melting of mantle peridotites in batch melting, isobaric fractional melting, and decompression melting, with a view to placing the OSMA array on a firmer theoretical foundation. The effects of water, bulk composition, Fe3+/Fe2+, temperature, and pressure on the mineralogy and phase chemistry in anhydrous and hydrous peridotites have also been modelled.
  The calculated results for anhydrous batch melting of fertile source peridotites KLB-1, KR4003, and MM3 using TH21* model agree well with experiments. In contrast, modelling hydrous melting was less successful, moving the focus of the results of this study to the residual products of volatile-free melting of Earth’s mantle in the context of the OSMA. Using anhydrous peridotite melting models, varying bulk Fe3+ had minimal effect on spinel stability. The solidus and the temperature of spinel stability for fertile peridotites are lower than for depleted peridotites. Adding alkalis can reduce the melting temperature of a lherzolite or a depleted peridotite source. With the TH21 model, spinel survives to a much higher degree of melting in batch melting (>40%) than fractional melting (85) in all melting models. The behaviour of Al and Cr during batch melting and the distribution coefficient of Al and Cr in spinel and melt have been studied to understand the varying spinel Cr# in residual peridotites.
  By studying decompression melting, with different bulk compositions following adiabats with distinct mantle potential temperatures, the evolution of mantle melting from Archean to present-day can be modelled more rigorously.

  *TH21: after Tomlinson and Holland (2021)

• Subjects / Keywords

  • Thermodynamic models
  • Mantle peridotites
  • Partial melting

• Graduation date

  Spring 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-w202-az17

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.