Zircon U-Pb-Hf isotopes and whole-rock geochemistry of gneissic granites from the Jitang complex in Leiwuqi area, eastern Tibet, China: Record of the closure of the Paleo-Tethys Ocean

Previous investigations have indicated that the Changning-Menglian (CMSZ) and Longmu Co-Shuanghu (LSSZ) suture zones represent the Paleo-Tethys Ocean of northern Tibet and western Yunnan of China, respectively. However, our understanding of the Paleo-Tethys suture zone in eastern Tibet seems to be incomplete. The North Lancangjiang suture zone (NLSZ) has been hypothesized to mark the Paleo-Tethys Ocean in eastern Tibet. The present study reports new zircon U-Pb ages and Hf isotope data, and whole-rock major and trace element data from the gneissic granites from the Jitang complex in the Leiwuqi area of the NLSZ in order to verify this hypothesis. Six samples of gneissic granites yielded weighted mean 206Pb/238U ages of 249-237 Ma. The geochemical data show that the gneissic granites are characterized by high SiO2 (70.79-77.75 wt.%); K2O (2.00-6.13 wt.%); low A/CNK values (< 1.1); enrichment in Rb, Th, Ba, and Pb; depletion in Nb, Ta, Sr, Ti, and P; and negative Eu anomalies. These features suggest that the gneissic granites were high-potassium, calc-alkaline, and I-type granites. Moreover, the zircon εHf(t) values (from − 2.7 to + 2.5) and TCDM model ages (1447-1009 Ma) indicate that they were generated by the partial melting of the Meso-proterozoic juvenile crust. These gneissic granites were interpreted to have formed in the post-collisional tectonic setting related to the closure of the Paleo-Tethys Ocean. By combining previously published and the new data, we propose that the NLSZ connects the LSSZ and CMSZ in the Tibetan plateau, and marks a Paleo-Tethys Ocean basin in eastern Tibet.