The North Altun Orogenic Belt, a key part of the Qinling-Qilian-Kunlun orogenic system, preserves critical records of the evolution of the Proto-Tethys Ocean. However, the timing of its tectonic transition from post-collisional compression to extension remains poorly constrained. This study presents detailed field investigations, zircon SIMS U-Pb dating, and whole-rock geochemical and Sr-Nd isotopic analyses of newly identified diabase dikes in the Kaladawan and Aktash areas in the North Altun terrane. Zircon U-Pb dating reveals that the diabases emplaced at ca. 441 Ma. The rocks are classified as tholeiitic basalts, exhibiting low MgO (4.07%~4.47%) and total alkali (Na2O+K2O=4.84%~5.82%) contents with relatively high Fe2O3T (16.18%~16.75%). They are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE) but depleted in high-field-strength elements(HFSE), displaying pronounced negative Nb-Ta-Zr-Hf-Ti anomalies on primitive mantle-normalized spider diagrams. Furthermore, their high initial 87Sr/86Sr ratios (0.7117~0.7125) and extremely low εNd(t) values (?20.0~?19.8) indicate derivation from an ancient lithospheric mantle which metasomatized by fluids released from subduction slab. These findings suggest that the diabases are direct products of post-orogenic extension, thus constraining the timing of the tectonic regime from compression to extension in the North Altun Orogenic Belt occurred at ca. 441 Ma.