The late Palaeozoic tectonic magmatism in the northern Qaidam tectonic belt (NQTB) related to the Palaeo-Tethys Ocean has become a critical issue. We performed a detailed geochronological and geochemical study of Lenghu (LH) granitic rocks in the western NQTB. LA–ICP–MS U–Pb dating of zircons from LH granitic rocks yields emplacement ages of 253 ± 4 Ma and 264 ± 4 Ma, indicating a two-stage emplacement process. Geochemical analyses show that the LH granitic rocks have low ACNK values and are enriched in LILEs (Rb, Th, Ba) and depleted in HFSEs (Sr, Nd, and Ta). The samples are enriched in LREEs (LREE/HREE =1.5–7.3). Values of (La/Yb)_N range between 0.9 and 6.5, and all samples show negative Eu anomalies (δEu =0.2–0.6), with typical characteristics of island arc magmatism. The LH granitic rocks have εHf(t) values of -3.7 to +8.0 and yield a TCDM age of 1.51-0.78 Ga. The data suggest that the LH granitic rocks were derived from partial melting of Proterozoic crust-related mafic to intermediate rocks with significant crust–mantle interactions. The results, combined with regional magmatic information, indicate that the Late Permian-early Triassic magmatism in western NQTB were controlled by subduction rollbackretraction of South Kunlun Oceanic plate under the Kunlun–Qaidam Block.