Zircon SIMS U-Pb dating and its significance of cumulate gabbro from Dengqen ophiolite，eastern Tibet, China

Dengqen ophiolite is located in the eastern of Bangong Co-Nujiang suture zone，and is composed of ultra-mafic rocks, mafic dykes, cumulate gabbro, pillow basalt and siliceous rocks. The geochemical data suggest that the Nayongla cumulate gabbros from Dengqen ophiolite maybe formed under the setting of MOR. Zircons from the cumulate gabbro are all magmatic origin according to their CL images and analytic data. SIMS U-Pb zircon age of 217.8 ± 1.6 Ma is obtained, which suggest that the Nayongla cumulate gabbro formed in Late Triassic. The age of Nayongla cumulate gabbro provides the exact time for the opening of Bangong Co－Nujiang ocean in Dengqen area.