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<p>Dunite channels are critical pathways for melt extraction and migration within the asthenosphere. Although their formation within mantle peridotite sequences is often attributed to melt-rock interaction, the underlying physical processes remain poorly constrained. This study examines variations in both major and trace elements across a dunite-harzburgite sequence in the Zedong ophiolite to better understand these physical processes. Geochemical profiles across the dunite-harzburgite transect reveal concentration gradients near the dunite-harzburgite contact, particularly within the harzburgite. Such compositional variations were interpreted through two-dimensional numerical simulations, coupled with diffusion and advection in porous media. The results indicate that trace element gradients in olivine can be produced by a melt flow along the dunite–harzburgite boundary with lateral advection from dunite to harzburgite, which is consistent with those observed in the field. Trace element patterns of the interstitial clinopyroxene grains within the dunite suggest their crystallization from a final pulse of percolating melt through the channel during the waning stage of the melt transport system, which probably occurred shortly before the ophiolite obduction. Integrating these results with previous studies on mafic–ultramafic rocks in the Moho Transition Zone (MTZ), we propose that the dunite–harzburgite sequence in the Zedong ophiolite was initially generated in the asthenosphere beneath an ultra-slow spreading ridge, which subsequently experienced a multi-stage history of melt migration and melt–rock interaction during progressive mantle upwelling. Such a complex history significantly influenced the lithological and geochemical architecture of the MTZ of the ophiolite. Overall, results from this study demonstrate that both dunites and their surrounding harzburgites bear variable concentration gradients, resulting from both mantle heterogeneity and variations in melt compositions within individual dunite channel.</p>

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Mantle heterogeneity and complicated melt migration revealed by chemical gradients across the dunite-harzburgite sequence in the Zedong ophiolite, South Tibet

  • 期刊论文

  • 发表日期：

    2026年1月9日

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  • Zhen-Yu Zhang,
  • Chuan-Zhou Liu,
  • Yan Liang,
  • Tong Liu,
  • Chang Zhang,
  • Bo-Da Liu

摘要

Dunite channels are critical pathways for melt extraction and migration within the asthenosphere. Although their formation within mantle peridotite sequences is often attributed to melt-rock interaction, the underlying physical processes remain poorly constrained. This study examines variations in both major and trace elements across a dunite-harzburgite sequence in the Zedong ophiolite to better understand these physical processes. Geochemical profiles across the dunite-harzburgite transect reveal concentration gradients near the dunite-harzburgite contact, particularly within the harzburgite. Such compositional variations were interpreted through two-dimensional numerical simulations, coupled with diffusion and advection in porous media. The results indicate that trace element gradients in olivine can be produced by a melt flow along the dunite–harzburgite boundary with lateral advection from dunite to harzburgite, which is consistent with those observed in the field. Trace element patterns of the interstitial clinopyroxene grains within the dunite suggest their crystallization from a final pulse of percolating melt through the channel during the waning stage of the melt transport system, which probably occurred shortly before the ophiolite obduction. Integrating these results with previous studies on mafic–ultramafic rocks in the Moho Transition Zone (MTZ), we propose that the dunite–harzburgite sequence in the Zedong ophiolite was initially generated in the asthenosphere beneath an ultra-slow spreading ridge, which subsequently experienced a multi-stage history of melt migration and melt–rock interaction during progressive mantle upwelling. Such a complex history significantly influenced the lithological and geochemical architecture of the MTZ of the ophiolite. Overall, results from this study demonstrate that both dunites and their surrounding harzburgites bear variable concentration gradients, resulting from both mantle heterogeneity and variations in melt compositions within individual dunite channel.