Petrogenesis of the Late Jurassic intrusive complex: An intra-oceanic arc case study in the Shiquanhe-Namucuo ophiolite mélange zone

Abstract The Shiquanhe-Namucuo ophiolite mélange zone (SNMZ) is a pivotal element of the Eastern Tethyan domain within the Tibet Plateau, marking the closure between the Northern and Central Lhasa subterranes. However, its tectonic evolution remains controversial regarding the tectonic setting (intra-oceanic arc versus continental margin), the timing of initial subduction, and the mechanism of ridge-trench interaction. Through zircon geochronology, zircon Hf isotopes, and whole-rock geochemistry, this study investigates the Late Jurassic Dong’e intrusive complex (ca. 166–159 Ma) in the western SNMZ’s Laguocuo area. Geochemical signatures supporting an intra-oceanic arc setting (e.g., low K2O and Th contents, positive εHf(t) values, large ion lithophile elements enrichment, and high field strength elements depletion), as well as crystal-melt separation textures, indicate derivation from a depleted mantle wedge modified by subduction components. We propose that the Shiquanhe-Namucuo Ocean experienced localized ridge expansion under regional compression during the Late Jurassic. This process drove the approach of a spreading ridge toward a younger subduction zone, triggering intra-oceanic arc maturation and island arc magmatism activation. These findings advance the understanding of ridge-trench interactions in this subduction event and highlight the SNMZ as a distinct remnant of the intra-oceanic arc within the Eastern Tethyan domain.