Abstract: Located on the northern margin of North China Block, the Baoxing rock mass is mainly composed of granodiorite. According to LA-ICP-MS zircon U-Pb dating, it was formed in Middle Triassic, with the ²⁰⁶Pb/²³⁸U age of 235.0±1.3Ma. The average K₂O/Na₂O ratio is 1.07, indicating that the rocks belong to high-K calc-alkaline series. The rocks are enriched in LILE and depleted in HFSE, showing typical features of calc-alkaline series on an active continental margin. The average total amount of REE is 147×10^-6, and the curve exhibits obvious right-inclined feature on REE distribution pattern, suggesting that the rocks are of the type of LREE enrichment and HREE depletion with medium negative Eu anomaly. According to the petrology, geochemistry and geochronology in combination with the tectonic evolution research on adjacent areas, lithospheric delamination occurred under the extension in the study area, and then caused a large-scale magmatic activity in the Middle Triassic.