Nitrogen and carbon fractionation during core-mantle differentiation at shallow depth
Nitrogen and carbon fractionation during core-mantle differentiation at shallow depth
复制标题
DOI：
10.1016/j.epsl.2016.10.026
复制
发表时间：
2017-01-15
影响因子：
5.3
通讯作者：
Armstrong, Lora S.
中科院分区：
文献类型：
--
作者：
Dalou, Celia;Hirschmann, Marc M.;Armstrong, Lora S.
关于太阳系中挥发性元素的最显着观察之一是相对于球粒陨石，块状硅酸盐地球（BSE）中的N耗尽，导致特别高的非球粒陨石C：N比。N耗竭可能反映了大规模的分化事件，如地球核心的封存或地球早期大气的大规模吹掉，或者后期添加的挥发物丰富的单板的特性。由于在早期行星分化过程中N的行为受到很大的限制，我们一起确定了Fe-N-C金属合金和两种不同的硅酸盐熔体（陆地和火星玄武岩）之间的N和C的分配。在1.2至3GPa和1400摄氏度或1600摄氏度下，条件跨越从Δ IW-0.4至Δ IW-3.5的f（O2）范围，其中Δ IW是实验102与结晶Fe和浮氏体共存所施加的值之间的对数差。（D-N（金属/硅酸盐））主要取决于f（O2），随着f（O2）的减小，D-N（金属/硅酸盐）从24 +/-3减小到0.3 +/-0.1。与此相反，C分配系数（D-C（金属/硅酸盐））显示没有证据的压力依赖性，但随着温度的降低。在1400摄氏度下，D-C（金属/硅酸盐）分配系数随着f（O2）从300 +/- 30降低到670 +/- 50而线性增加。然而，在1600摄氏度时，它们从Delta IW-0.7增加到Delta IW-2（87 +/- 3到240 +/- 50），并从Delta IW-2减少到Delta IW-3.3（99 +/- 6）。在高温下，在还原条件下，熔体中增强的C可能反映了C-H物种（最有可能是CH 4）的稳定化。对于N或C的分配没有明显的成分依赖性，这可能是由于所研究的玄武岩比较相似。在适度还原条件下（Δ IW-0.4至-2.2），N在成核金属中比在熔融硅酸盐中更相容（1
One of the most remarkable observations regarding volatile elements in the solar system is the depletion of N in the bulk silicate Earth (BSE) relative to chondrites, leading to a particularly high and non-chondritic C:N ratio. The N depletion may reflect large-scale differentiation events such as sequestration in Earth's core or massive blow off of Earth's early atmosphere, or alternatively the characteristics of a late-added volatile-rich veneer. As the behavior of N during early planetary differentiation processes is poorly constrained, we determined together the partitioning of N and C between Fe-N-C metal alloy and two different silicate melts (a terrestrial and a martian basalt). Conditions spanned a range of f(O2) from Delta IW-0.4 to Delta IW-3.5 at 1.2 to 3 GPa, and 1400 degrees C or 1600 degrees C, where Delta IW is the logarithmic difference between experimental 102 and that imposed by the coexistence of crystalline Fe and wustite.N partitioning (D-N(metal/silicate)) depends chiefly on f(O2), decreasing from 24 +/- 3 to 0.3 +/- 0.1 with decreasing f(O2)center dot D-N(metal/silicate) also decreases with increasing temperature and pressure at similar f(O2), though the effect is subordinate. In contrast, C partition coefficients (D-C(metal/silicate)) show no evidence of a pressure dependence but diminish with temperature. At 1400 degrees C, D-C(metal/silicate) partition coefficients increase linearly with decreasing f(O2) from 300 +/- 30 to 670 +/- 50. At 1600 degrees C, however, they increase from Delta IW-0.7 to Delta IW-2 (87 +/- 3 to 240 +/- 50) and decrease from Delta IW-2 to Delta IW-3.3 (99 +/- 6). Enhanced C in melts at high temperatures under reduced conditions may reflect stabilization of C-H species (most likely CH4). No significant compositional dependence for either N or C partitioning is evident, perhaps owing to the comparatively similar basalts investigated.At modestly reduced conditions (Delta IW-0.4 to -2.2), N is more compatible in core-forming metal than in molten silicate (1