School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
Department of Earth Sciences, University College London, London WC1E 6BT, UK.
Nature. 2016 Jan 7;529(7584):76-9. doi: 10.1038/nature16174.
Interactions between crustal and mantle reservoirs dominate the surface inventory of volatile elements over geological time, moderating atmospheric composition and maintaining a life-supporting planet. While volcanoes expel volatile components into surface reservoirs, subduction of oceanic crust is responsible for replenishment of mantle reservoirs. Many natural, 'superdeep' diamonds originating in the deep upper mantle and transition zone host mineral inclusions, indicating an affinity to subducted oceanic crust. Here we show that the majority of slab geotherms will intersect a deep depression along the melting curve of carbonated oceanic crust at depths of approximately 300 to 700 kilometres, creating a barrier to direct carbonate recycling into the deep mantle. Low-degree partial melts are alkaline carbonatites that are highly reactive with reduced ambient mantle, producing diamond. Many inclusions in superdeep diamonds are best explained by carbonate melt-peridotite reaction. A deep carbon barrier may dominate the recycling of carbon in the mantle and contribute to chemical and isotopic heterogeneity of the mantle reservoir.
在地质时间内，地壳和地幔储层之间的相互作用主导着挥发性元素的地表储量，调节大气成分并维持一个适合生命存在的行星。虽然火山将挥发性成分排放到地表储层中，但大洋地壳的俯冲则负责补充地幔储层。许多起源于深部上地幔和过渡带的天然“超深”钻石含有矿物包裹体，表明它们与俯冲大洋地壳有亲和力。在这里，我们表明，大多数板块地热梯度将在大约 300 至 700 公里的深度沿着碳酸化大洋地壳的熔融曲线相交一个深部凹陷，从而形成了将碳酸盐直接循环到深部地幔的障碍。低度部分熔融是碱性碳酸盐岩，与还原的周围地幔高度反应，产生钻石。超深钻石中的许多包裹体最好通过碳酸盐熔体-橄榄岩反应来解释。深部碳障可能主导地幔中碳的再循环，并导致地幔储层的化学和同位素不均匀性。
