Origin and multi-episodic melt/fluid interactions revealed by the subducted serpentinites in the North Qilian Belt, NW China: Implications for the compositional heterogeneity of the fossil oceanic mantle

• Published in: Journal of Asian earth sciences Vol. 271; p. 106237
• Main Authors: Zhang, Miao, Zhao, Jing, Guo, Jia, Chen, Xi, Peng, Xiuhong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.07.2024
• Subjects: Compositional heterogeneity; Melt/fluid-rock interaction; North Qilian Belt; Petrogenesis; Subducted serpentinite; Melt/fluid-rock interaction; North Qilian Belt; Compositional heterogeneity; Petrogenesis; Subducted serpentinite
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2024.106237

[Display omitted] •The serpentinites were derived from the subducted lithospheric mantle.•They recorded a multi-episodic evolution of melt/fluid metasomatism in subduction zone.•The fossil mantle of North Qilian Ocean is compositionally heterogeneous. In nature, serpentinites act as reservoirs of water and fluid-mobile elements and play an essential role in arc magmatism, fluid metasomatism, and elemental circulation in subduction zones. This paper presents new mineral and whole-rock geochemical analyses of the Qingshuigou serpentinite massif and discusses its petrogenesis, tectonic setting, and mantle metasomatism. The chemical composition (e.g., REE, Y, Mg, and Al) and petrological observations (e.g., pseudomorph and hourglass textures) of serpentines demonstrate that the serpentinites’ protoliths belong to the peridotites. Their degrees of partial melting were estimated to be 15–20 % using Yb, Cr, Ti, and HREEs, indicating that these peridotite protoliths were residual in origin after high degrees of mantle melting. They were relics of the subducted lithospheric mantle in the subduction zone, based on their geochemical similarities with subducted serpentinites. Notably, the Qingshuigou serpentinites show several geochemical fingerprints of melt-rock interactions, such as the U-shaped REE patterns, elevated Zr/Ti, Zr/Hf, and Nb/Ta ratios; this led us to propose that the peridotite protoliths of the serpentinites were not merely melting remnants but were significantly modified by melt metasomatism. Also, they experienced two stages of fluid/rock interactions in the subduction zone: early-stage serpentinization at shallow depths and lizardite/chrysotile to antigorite transition at an elevated depth. Combined with the published data of ophiolitic peridotites from the North Qilian Belt, the compositional heterogeneity of these peridotites and associated serpentinites might be associated with the nature of melt/fluid metasomatism under different geodynamic backgrounds.