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尖晶石具有高Os低Re含量的特性,能够抵抗变质、蚀变和风化作用对其Os同位素组成的影响,其Os同位素组成的测量值可以代表形成时的初始Os同位素组成.本文尝试用同一堆晶序列纯橄岩中尖晶石Os同位素组成和辉长岩中锆石年龄来反演地幔源区的Os同位素组成,为认识大洋岩石圈的形成和演化提供重要证据.西藏那曲蛇绿岩是新特提斯蛇绿岩的一部分,位于班公湖-怒江缝合带中段,形成于成熟的弧后盆地,其中发育同一堆晶序列的纯橄岩和辉长岩.辉长岩中锆石U-Pb年龄为183.7±1Ma.纯橄岩的全岩和分选出的尖晶石的Os同位素组成非常一致,排除了后期混染作用的影响,可以代表对流上地幔Os同位素组成.与碳质球粒陨石对比,尖晶石的?Os为?0.2～?0.3,表明那曲蛇绿岩的地幔源区为碳质球粒陨石型对流上地幔.因此,青藏高原大陆岩石圈主体属于残留的特提斯大洋岩石圈,是由中生代软流圈地幔顶部转化形成.这是首次运用能准确定年的堆晶岩中尖晶石Re-Os同位素组成来反演蛇绿岩地幔源区性质的研究实例.
The spinel has the characteristics of high Os low Re content, which can resist the influence of metamorphism, alteration and weathering on the Os isotopic composition of the spinel, and its Os isotopic composition measurement can represent the initial Os isotope composition during the formation. The Os isotopic composition of spinel and the zircon age of gabbro in the hematite sequence of the hematite sequence are used to invert the Os isotopic composition of the mantle source region and provide important evidence for understanding the formation and evolution of the oceanic lithosphere. Is part of the Neo-Tethyan ophiolite, located in the middle part of the Bangong-Nujiang suture zone and formed in a mature back-arc basin with the development of dunites and gabbros of the same plutonic sequence. The U-Pb age is 183.7 ± 1Ma.The Os isotopic composition of the whole rock and the sorted spinel of the dunite rock is very consistent, excluding the influence of late-stage mixing and can represent the Os isotope composition of the convective upper mantle. Compared with the mass chondrites, the Os of the spinel is 0.2 ~ 0.3, indicating that the mantle source area of the Naqu ophiolite is a carbonaceous chondrite-type convective upper mantle, therefore, the main lithosphere in the continental Tibetan Plateau belongs to the residual The Tethyan Oceanosphere is made of The top of the child generation conversion asthenospheric mantle is formed. This is the first use of the heap of rock crystal spinel Re-Os isotopic composition can accurately be given in Examples inversion ophiolite mantle properties.