Zircon U-Pb ages of the Dongbo ophiolite in the western Yarlung Zangbo suture zone and their geological significance.
西藏雅鲁藏布江缝合带西段东波蛇绿岩中锆石U-Pb定年及地质意义

The Dongbo ophiolite in the western Yarlung Zangbo suture zone contains mantle peridotite, pyroxenite and gabbro. The mantle peridotite consists of harzburgite, dunite and minor lherzolite. Some pyroxenite and gabbro veins of variable size occur in mantle peridotite, and most of them strike NW, parallel to the main structure of the mantle peridotite. The pyroxenite consists of about 90% diopside (Wo=48, En=46, Fs=6), 5% plagioclase (An=90) and small amounts of clinoenstatite (Wo=2, En=82, Fs=16) and tremolite. The gabbro contains pyroxene (Wo=47, En=36, Fs=17), plagioclase (An=47) and minor magnesium amphibole. The gabbros are characterized by low contents of K2O (<0.1%) and P2O5 (<0.1%), and depleted LREE patterns, similar to that of N-MORB. U-Pb dating of zircons from the pyroxenite and gabbro by LA-ICP-MS yielded ages of 130±0.5Ma and 128±1.1Ma, respectively. These data provide the first age constraint on the Dongbo ophiolite, and show that it belongs to the Neo-Tethyan system of the Yarlung Zangbo suture zone.