Fe–Ni–Cu–C–S phase relations at high pressures and temperatures – The role of sulfur in carbon storage and diamond stability at mid- to deep-upper mantle
Fe–Ni–Cu–C–S phase relations at high pressures and temperatures – The role of sulfur in carbon storage and diamond stability at mid- to deep-upper mantle
复制标题
高压高温下的 Fe-Ni-Cu-C-S 相关系 – 硫在上地幔中深层碳储存和金刚石稳定性中的作用
DOI：
10.1016/j.epsl.2014.12.018
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发表时间：
2015
影响因子：
5.3
通讯作者：
R. Dasgupta
中科院分区：
文献类型：
--
作者：
K. Tsuno;R. Dasgupta
制约碳在深部地幔中的稳定形式是重要的，因为碳对地幔过程（如部分熔融和元素活动性）具有关键影响，从而影响内生和外生储层之间的碳交换效率。在还原的中深上地幔中，深部碳的主要宿主预计是石墨/金刚石，但在还原地幔中存在Fe-Ni合金熔体的情况下，由于碳在这种合金相中的高溶解度，金刚石可能变得不稳定。为了研究还原中深上地幔中稳定含碳相的性质，我们利用多砧压力机在6-8 GPa和800-1400° C下，研究了硫对Fe-Ni±Cu-C-S系统富Ni部分相关系的影响，以及碳在Fe-Ni固体和Fe-Ni-S液态合金中的溶解度。对六种起始混合物（Ni/（Fe+ Ni）≤ 0.61，8-16重量%）进行低温实验S）含有含C的固体Fe-Ni合金+ Fe-Ni-C-S合金熔体+亚稳石墨，并且固体合金外边界受到约束，对于贫S起始混合物在1150-1200° C在6 GPa下和900-1000° C在8 GPa下，并且对于富S起始混合物在1000-1050° C在6 GPa下和900-1000° C在8 GPa下。液态合金中的碳溶解度从2.1wt%显着降低到0.8wt%熔体中的硫从8重量%增加到24重量%，而与温度无关。我们还观察到，当合金液中含有> 0.18wt.%的碳时，随着压力的增加，碳在液态合金中的溶解度略有降低。Ni/（Fe+ Ni）比从0.65降低到0.53。根据我们的研究结果，金刚石，与富镍硫化物液态合金共存，预计将是稳定的还原，含合金的海洋地幔与C含量低至20至5 ppm的地幔S在100和200 ppm之间变化。另一方面，深，还原根的地幔，预计有C分布在固体合金，液体合金，和金刚石之间的低S（≤ 100 ppm S）域和液体合金和金刚石之间的高S（≥ 150 ppm S）域。我们的研究结果可以解释富镍硫化物和/或Fe-Ni合金夹杂物在金刚石中的观察，并表明金刚石在含合金的还原地幔中的稳定性并不一定需要来自回收的地壳岩性的过量C供应。我们预测，由于与地幔硫化物的相互作用，金刚石在亏损的上地幔背景下稳定，这也与橄榄岩金刚石的碳同位素组成（δ 13 C为− 5±1‰）一致，这表明没有来自循环碳的重要输入。
Constraining the stable form of carbon in the deep mantle is important because carbon has key influence on mantle processes such as partial melting and element mobility, thereby affecting the efficiency of carbon exchange between the endogenic and exogenic reservoirs. In the reduced, mid-to deep-upper mantle, the chief host of deep carbon is expected to be graphite/diamond but in the presence of Fe–Ni alloy melt in the reduced mantle and owing to high solubility of carbon in such alloy phase, diamond may become unstable. To investigate the nature of stable, C-bearing phases in the reduced, mid-to deep-upper mantle, here we have performed experiments to examine the effect of sulfur on the phase relations of the Ni-rich portion of Fe–Ni±Cu–C–S system, and carbon solubility in the Fe–Ni solid and Fe–Ni–S liquid alloys at 6–8 GPa and 800–1400° C using a multianvil press. Low-temperature experiments for six starting mixes (Ni/(Fe+ Ni)∼ 0.61, 8–16 wt.% S) contain C-bearing, solid Fe–Ni alloy+ Fe–Ni–C–S alloy melt+ metastable graphite, and the solid alloy–out boundary is constrained, at 1150–1200° C at 6 GPa and 900–1000° C at 8 GPa for S-poor starting mix, and at 1000–1050° C at 6 GPa and 900–1000° C at 8 GPa for the S-rich starting mix. The carbon solubility in the liquid alloy significantly diminishes from 2.1 to 0.8 wt.% with sulfur in the melt increasing from 8 to 24 wt.%, irrespective of temperature. We also observed a slight decrease of carbon solubility in the liquid alloy with increasing pressure when alloy liquid contains>∼ 18 wt.% S, and with decreasing Ni/(Fe+ Ni) ratio from 0.65 to∼ 0.53. Based on our results, diamond, coexisting with Ni-rich sulfide liquid alloy is expected to be stable in the reduced, alloy-bearing oceanic mantle with C content as low as 20 to 5 ppm for mantle S varying between 100 and 200 ppm. Deep, reduced root of cratonic mantle, on the other hand, is expected to have C distributed among solid alloy, liquid alloy, and diamond for low-S (≤ 100 ppm S) domains and between liquid alloy and diamond in high-S (≥ 150 ppm S) domains. Our findings can explain the observation of Ni-rich sulfide and/or Fe–Ni alloy inclusions in diamond and suggest that diamond stability in the alloy-bearing, reduced mantle does not necessarily require excess C supply from recycled, crustal lithologies. Our prediction of diamond stability in the background, depleted upper mantle, owing to the interaction with mantle sulfides, is also consistent with the carbon isotopic composition of peridotitic diamond (δ 13 C of− 5±1‰), which suggests no significant input from recycled carbon.
影响因子：
64.8
作者：
Stagno, Vincenzo;Ojwang, Dickson O.;Frost, Daniel J.
通讯作者：
Frost, Daniel J.
影响因子：
3.5
作者：
Bulanova, Galina P.;Walter, Michael J.;Gobbo, Luiz
通讯作者：
Gobbo, Luiz