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标签: 金刚石
摘要 : 本期Nature封面所示为一块有包膜的“脏”金刚石,是当一个含微包裹体的纤维膜生长在一块单晶清透金刚石上时生成的。


本期Nature封面所示为一块有包膜的“脏”金刚石,是当一个含微包裹体的纤维膜生长在一块单晶清透金刚石上时生成的。在地球表面附近发现的大多数金刚石都是在古老大陆最底部深度超过150公里处形成的。因此,“脏”金刚石中封存的化学杂质含有关于地球深处这些人们无法接触到的区域的宝贵信息。Yaakov Weiss及同事发表了来自加拿大西北地区Ekati金刚石矿的一组11块金刚石内所含包裹体的地球化学数据。这些数据包含清晰的化学演化趋势,它表明高咸度溶液参与了含硅和含碳酸盐的深层地幔熔融体的形成。含盐流体的化学性质和主体金刚石形成的时间说明,北美地下的一个消减板块是这些流体的来源,也说明在消减、地幔交代变质和富含流体的金刚石形成之间存在密切联系。这一新模型为了解地幔流体组成范围的效应提供了一个背景,这种效应会在全球范围内改变深层岩石圈,并在金刚石形成中起关键作用。封面: Graham Pearson


Highly saline fluids from a subducting slab as the source for fluid-rich diamonds


The infiltration of fluids into continental lithospheric mantle is a key mechanism for controlling abrupt changes in the chemical and physical properties of the lithospheric root, as well as diamond formation, yet the origin and composition of the fluids involved are still poorly constrained. Such fluids are trapped within diamonds when they form and so diamonds provide a unique means of directly characterizing the fluids that percolate through the deep continental lithospheric mantle. Here we show a clear chemical evolutionary trend, identifying saline fluids as parental to silicic and carbonatitic deep mantle melts, in diamonds from the Northwest Territories, Canada. Fluid–rock interaction along with in situ melting cause compositional transitions, as the saline fluids traverse mixed peridotite–eclogite lithosphere. Moreover, the chemistry of the parental saline fluids—especially their strontium isotopic compositions—and the timing of host diamond formation suggest that a subducting Mesozoic plate under western North America is the source of the fluids. Our results imply a strong association between subduction, mantle metasomatism and fluid-rich diamond formation, emphasizing the importance of subduction-derived fluids in affecting the composition of the deep lithospheric mantle.

来源: Nature 浏览次数:5


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