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The lithospheric-to-lower-mantle carbon cycle recorded in superdeep diamonds

机译：在Superdeep钻石中记录的岩石树脂型碳循环

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摘要

The transport of carbon into Earth's mantle is a critical pathway in Earth's carbon cycle, affecting both the climate and the redox conditions of the surface and mantle. The largest unconstrained variables in this cycle are the depths to which carbon in sediments and altered oceanic crust can be subducted and the relative contributions of these reservoirs to the sequestration of carbon in the deep mantle~(1). Mineral inclusions in sublithospheric, or 'superdeep', diamonds (derived from depths greater than 250 kilometres) can be used to constrain these variables. Here we present oxygen isotope measurements of mineral inclusions within diamonds from Kankan, Guinea that are derived from depths extending from the lithosphere to the lower mantle (greater than 660 kilometres). These data, combined with the carbon and nitrogen isotope contents of the diamonds, indicate that carbonated igneous oceanic crust, not sediment, is the primary carbon-bearing reservoir in slabs subducted to deep-lithospheric and transition-zone depths (less than 660 kilometres). Within this depth regime, sublithospheric inclusions are distinctly enriched in~(18)O relative to eclogitic lithospheric inclusions derived from crustal protoliths. The increased~(18)O content of these sublithospheric inclusions results from their crystallization from melts of carbonate-rich subducted oceanic crust. In contrast, lower-mantle mineral inclusions and their host diamonds (deeper than 660 kilometres) have a narrow range of isotopic values that are typical of mantle that has experienced little or no crustal interaction. Because carbon is hosted in metals, rather than in diamond, in the reduced, volatile-poor lower mantle~(2), carbon must be mobilized and concentrated to form lower-mantle diamonds. Our data support a model in which the hydration of the uppermost lower mantle by subducted oceanic lithosphere destabilizes carbon-bearing metals to form diamond, without disturbing the ambient-mantle stable-isotope signatures. This transition from carbonate slab melting in the transition zone to slab dehydration in the lower mantle supports a lower-mantle barrier for carbon subduction.
机译：碳的运输到地球的地幔中是地球碳循环中的关键途径，影响了气候和地幔的氧化还原条件。该循环中最大的无约束变量是沉积物中碳和改变的海外地壳的深度可以被压制和这些储存器对深层裂缝〜（1）中碳的封存的相对贡献。副间隔内的矿物质夹杂物或“超级Deep”，钻石（来自大于250公里的深度）可用于约束这些变量。在这里，我们呈现来自Kankan的钻石内的矿物质含量测量来自Kankan的矿物质含量，这些豚鼠从岩石圈延伸到较低地幔（大于660公里）。这些数据与碳金刚石的碳和氮同位素含量相结合，表明碳酸碎石的海底，而不是沉积物，是压滤到深层岩石和过渡区深度的平板中的初级碳储存器（小于660公里） 。在该深度方案中，相对于衍生自包裹促果实的野生岩体夹杂物，在〜（18）o中明显富集副间夹杂物。这些副间夹杂物的含量增加〜（18）o含量由它们从富含碳酸盐的底层海底熔体的结晶产生的。相比之下，较低的地幔矿物质夹杂物及其宿主钻石（深于660公里）的狭窄范围的同位素值，典型的披风似乎经历了很少或没有地壳互动。因为碳在金属中载入，而不是在金刚石中，因此在减少的挥发性较低的下露地〜（2）中，必须动集并浓缩碳以形成较低的披风钻石。我们的数据支持一种模型，其中通过化脓性海洋岩石圈的最上面的下部地幔的水合使碳含碳金属变得稳定，形成金刚石，而不会扰乱环境 - 地幔稳定同位素特征。从碳酸盐板在过渡区中熔化到下部地幔中的碳酸盐板熔化的过渡支撑用于碳俯冲的较低地幔屏障。

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  • 来源
    《Nature》 |2020年第7824期|234-238|共5页
  • 作者

    M E Regier; D G Pearson; T Stachel; R W Luth; R A Stern; J W Harris;

  • 作者单位

    Canadian Centre for Isotopic Microanalysis Department of Earth and Atmospheric Sciences University of Alberta;

    Canadian Centre for Isotopic Microanalysis Department of Earth and Atmospheric Sciences University of Alberta;

    Canadian Centre for Isotopic Microanalysis Department of Earth and Atmospheric Sciences University of Alberta;

    Canadian Centre for Isotopic Microanalysis Department of Earth and Atmospheric Sciences University of Alberta;

    Canadian Centre for Isotopic Microanalysis Department of Earth and Atmospheric Sciences University of Alberta;

    School of Geographical and Earth Sciences University of Glasgow;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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