A Middle Permian Intrusive Complex in the Xiwanggou Area, East Kunlun Orogen, China: Evidence for Palaeo-Tethys Ocean Subduction Initiation

ABSTRACT This study presents comprehensive analyses of an intrusive complex newly identified in the Xiwanggou area of the East Kunlun Orogen (EKO), encompassing mafic-ultramafic rocks and coeval granitic dykes. Integrating whole-rock geochemistry, zircon U-Pb geochronology, and Lu-Hf isotope data, we constrain the petrogenesis of the complex and its implications for regional tectonic evolution. Zircon U-Pb dating results show that the gabbros and granitic dykes yielded weighted mean ages of 269.6±1.1 and 265.9±1.0 Ma, respectively, indicating their emplacement during the middle Permian. Geochemically, both rock types exhibit low total Rare Earth Element ( Σ REE) contents with slight Light REE (LREE) enrichment, along with notable enrichment in Th, Zr, U, and Rb and depletion in Ti, P, Nb, and Sr. These signatures suggest involvement of continental crustal material and subduction-derived fluids in the magma system during ascent. Zircon εHf(t) values of the complex range from 2.9 to 19.3, all positive, reflecting a depleted mantle source with possible contributions from juvenile crust. Combined with regional tectonic context, our data demonstrate that the Xiwanggou complex formed between 270-260 Ma in response to the subduction of the A’nyemaqen oceanic crust and associated lithospheric mantle underplating. This finding provides robust geochronological evidence that the northward subduction of the Palaeo-Tethys Ocean (PTO) beneath the EKO initiated no later than 270 Ma (middle Permian), refining the timing framework of PTO evolution in the EKO.