中文摘要：

在 Nagqu ophiolite 的使早结晶的 chromian 尖晶石(Cr 尖晶石) 有高 O 和低 Re 内容，并且它在 serpentinization 期间对改变抵抗，捱过并且变态。原始岩浆的化学作文在 Cr 尖晶石被保存，它为决定披风来源的起始的 Os 同位素作文使它合适。这研究介绍 Cr 尖晶石 O 同位素和锆石 U-Pb 年龄为分别地，在一样堆积纯橄榄岩和斑粝岩在西藏在 Nagqu 堆积 ophiolite 的节。结果使 lithospheric 披风的形成和进化清楚些。Nagqu ophiolite 位于 Bangong-Nujiang 缝术地区的中央部分。它是 Neotethyan 海洋的外壳的残余，并且包含堆积纯橄榄岩和斑粝岩。从斑粝岩的锆石产出 183.7 的加权的吝啬的 206Pb/238U 年龄 ?  ?$

英文摘要：

Early-crystallizing chromian spinel （Cr-spinel） in the Nagqu ophiolite has high Os and low Re contents, and it is resistant to alteration during serpentinization, weathering and metamorphism. The chemical composition of primitive magma is preserved in Cr-spinel, which makes it suitable for determining the initial Os-isotope composition of the mantle source. This study presents Cr-spinel Os isotopes and zircon U-Pb ages for cumulate dunite and gabbro, respectively, in the same cumulate section of the ophiolite at Nagqu in Tibet. The results shed light on the formation and evolution of lithospheric mantle. The Nagqu ophiolite is located in the central part of the Bangong-Nujiang suture zone. It is a remnant of the Neotethyan oceanic crust, and contains cumulate dunite and gabbro. Zircon from the gabbro yielded a weighted mean 206pb/238U age of 183.7±1 Ma. Cr-spinel exhibits γos values of -0.2 to -0.3, suggesting that the mantle source for the dunite is similar to that of carbonaceous chondrites. Thus, the Tibetan lithosphere is primarily a relic of Tethyan oceanic lithosphere, which has formed by the transformation of the normal asthenospheric mantle in the Mesozoic. This is the first study to combine the spinel Os isotopes with accurate zircon U-Pb ages to constrain the geochemical characteristics of the mantle source for the ophiolite.