Late Triassic Magmatism in the Eastern Section of the North Qilian Orogenic Belt and Its Tectonic Implications: Insights From the Shilijia Monzogranite Dyke

While extensive research has been conducted on the Early Palaeozoic tectonic evolution of the North Qilian Orogenic Belt, its Late Triassic tectono‐magmatic history remains poorly understood. Controversies persist regarding the tectonic setting, ages and geodynamic setting of magmatic activity in the eastern North Qilian Orogenic Belt, which negative our comprehension of the region's post‐collisional evolutionary processes. Clarifying these events is crucial for reconstructing the final stages of the Paleo‐Tethys Ocean closure and the conjunction between the Qilian and Qinling Orogenic Belts. This study determined that the Shilijia monzogranite dyke formed during the Late Triassic (Norian), with 206 Pb/ 238 U weighted mean ages of 213.5 ± 1.5 Ma and 214.5 ± 2.3 Ma. Geochemically, the dyke is characterised by high SiO 2 and alkali contents, low Al 2 O 3 content, and an aluminium saturation index (A/CNK) ranging from 1.00 to 1.06. The dyke is enriched in large‐ion lithophile elements (LILEs) such as Rb, and in high‐field‐strength elements (HFSEs) including Th and U, but depleted in Ba, Ta, Nb, Sr, P, Eu and Ti. The high‐field‐strength elements (Zr + Nb + Ce + Y) range from 389.70 to 622.39 ppm, while the rare earth element (REE) concentrations vary from 252.94 to 460.24 ppm, exhibiting a ‘seagull‐shaped’ distribution pattern and indicating negative Eu anomalies. The K 2 O/Na 2 O ratio of the Shilijia monzogranite dyke ranges from 1.37 to 1.54, with F content below 1000 ppm. Biotite dominates the dark minerals, and plagioclase mineral content is relatively high. Geochemical characteristics suggest that the Shilijia monzogranite dyke formed in a post‐orogenic extensional environment, marking the end of the Late Triassic North Qilian orogenic event and the closure of the Paleo‐Tethys Ocean. In conjunction with regional geological information, the Shilijia dyke shares similarities with granites from the Qinling Orogenic Belt, thereby provide support for the region was transitioning from a post‐orogenic to an anorogenic setting at the end of the Late Triassic.