LA-ICP-MS U-Pb zircon, columbite-tantalite and ⁴⁰Ar-³⁹Ar muscovite age constraints for the rare-element pegmatite dykes in the Altai orogenic belt, NW China

The Chinese Altai is renowned for its rich rare-element resources. Nine representative rare-element (REL) pegmatites were dated using LA-ICP-MS and ⁴⁰Ar-³⁹Ar methods. The columbite grains yield a weighted mean ²⁰⁶Pb/²³⁸U age of 239.6±3.8 Ma for the Dakalasu (Be-Nb-Ta) pegmatite and concordia U-Pb ages of 258.1±3.1 Ma and 262.3±2.5 Ma for the Xiaokalasu (Li-Nb-Ta) pegmatite. The zircons display a weighted mean ²⁰⁶Pb/²³⁸U age of 198.5±2.5 Ma for the Husite (Be) pegmatite and concordia U-Pb ages of 194.3±1.6 Ma and 248.2±2.2 Ma for the Qunkuer (Be) and Taerlang (barren) pegmatites. The muscovite ⁴⁰Ar-³⁹Ar dating gives plateau ages of 286.4±1.6 Ma, 297.0±2.6 Ma, 265.2±1.5 Ma, 178.8±1.0 Ma, 162.2±0.9 Ma, 237.7±1.3 Ma, 237.4±1.2 Ma and 231.9±1.2 Ma for the Talate (Li-Be-Nb-Ta), Baicheng (Nb-Ta), Kangmunagong (barren), Husite (Be), Qunkuer (Be-Nb-Ta), Xiaokalasu (Li-Nb-Ta), Weizigou (Be) and Taerlang (barren) pegmatites, respectively. These new ages coupled with previous geochronological work suggest that the REL pegmatites in the Chinese Altai formed during early Permain - Late Jurassic time. The REL pegmatites located in the Central Altaishan terrane are younger than those in the Qiongkuer-Abagong terrane, showing a correlation with the coeval and adjacent granites. The formation of the REL pegmatites and these granites indicates frequent and strong magmatic activity in the post-orogenic and anorogenic setting. The spatial and temporal distribution of pegmatites and granites reveals a magmatism path from the SE (of age early-middle Permian), to the NW (middle Permian - Middle Triassic) and finally to the central part (Middle Triassic - Jurassic) of the Chinese Altai.