Geochronological and deformation constraints on the crystallization and cooling evolution of lithium pegmatites in the Huanglongling–Tashidaban Orefield, Altyn Tagh, NW China

The discovery of the Huanglongling-Tashidaban giant lithium ore-field represents a major breakthrough within the Altyn Tagh metallogenic belt. However, the precise timing and the cooling history remain poorly constrained. Here, we integrate in- situ Rb-Sr and 40 Ar/ 39 Ar geochronology on lepidolite from lithium-bearing pegmatites, quartz geochemistry, and electron backscatter diffraction (EBSD) analysis. These data directly constrain the age of lithium mineralization and reconstruct the evolution from crystallization and emplacement to cooling processes. In- situ Rb-Sr dating of lepidolite yields two distinct age clusters: 431–424 Ma and 382–379 Ma. The 40 Ar/ 39 Ar plateau ages of the Huanglongling pegmatites range from 383 to 370 Ma, whereas Tashidaban pegmatites yield a plateau age of 322 Ma. These 40 Ar/ 39 Ar data delineate distinct cooling paths and the geochronological results reveal markedly different cooling histories. The early-stage magmatic-pegmatitic event in Huanglongling-Tashidaban area was followed by protracted and complex cooling. In contrast, late-stage pegmatites at Huanglongling record rapid emplacement and efficient cooling. The ore field thus preserves evidence of multi-stage magmatism and differential cooling. Quartz microstructres commonly display bulging recrystallization, subgrain rotation. EBSD analyses analyses indicating significant crystal-plastic deformation during cooling. Ti-in-quartz thermometry reveals average deformation temperatures of (334–420) °C for Huanglongling, and higher than those in Tashidaban (302–337) °C. Our results indicate that Huanglongling area was proximal to the magmatic-pegmatitic center, whereas Tashidaban area represents a distal or peripheral domain. The age of lepidolite constrains the timing of lithium evolution from crystallization and emplacement to cooling. This study provides new constraints on the complex deformation-cooling processes associated with granitic pegmatite emplacement.