The HighPGibbs program is designed to calculate thermodynamic equilibrium of fluid‐rock systems up to depths of lithospheric mantle. It uses the Gibbs free energy minimization function of the HCh package to calculate mineral‐fluid equilibrium. Chemical potentials of minerals are calculated using the equations of states included in HCh; free energy of aqueous species is calculated using the Deep Earth Water model; and activity coefficients of charged species are estimated using the Davies variant of the Debye‐Hückel equation. HighPGibbs was applied to calculate nitrogen speciation in eclogite‐buffered fluids from 400 to 790 °C and 30 to 54 kbar, to evaluate the mobility of nitrogen in subducting oceanic crust. Regardless of whether the protolith was altered (and oxidized) or not, N₂(aq) or NH₃(aq) is the predominant form of nitrogen in the slab fluids at subarc temperatures, especially in cases of moderate or hot geotherms. Given that molecular nitrogen is highly incompatible in silicate minerals, the simulation indicates that nitrogen (as NH₄⁺) in silicate minerals can be liberated during metamorphic devolatilization. The majority of nitrogen in subducting crusts can be unlocked during slab devolatilization and eventually expelled to the atmosphere via degassing of arc magmas. Therefore, oceanic crusts recycled to deep Earth will be depleted in nitrogen compared to the newly formed crust at spreading centers. As a result of the long‐term mantle convection, large proportions of the bulk silicate Earth may have suffered nitrogen extraction via subduction, and this may account for the nitrogen enrichment in the Earth's atmosphere.

中文翻译：

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HighPGibbs，一种用于深地球流体-岩石热力学模拟的实用工具及其在俯冲带流体中氮形态计算中的应用

HighPGibbs程序旨在计算直至岩石圈地幔深度的流体岩石系统的热力学平衡。它使用六氯环己烷包装的吉布斯自由能最小化函数计算矿物-流体平衡。矿物的化学势是使用六氯环己烷中包含的状态方程计算的；含水物种的自由能使用“深水模型”计算；使用Debye-Hückel方程的Davies变体估算带电物种的活度系数。HighPGibbs用于计算在400至790°C和30至54 kbar的榴辉岩缓冲流体中的氮形态，以评估俯冲洋壳中氮的迁移率。不论原生石是否被改变（和氧化），N ₂（aq）或NH ₃（aq）是亚弧温度下板状流体中氮的主要形式，尤其是在中等或高温地热的情况下。考虑到分子氮与硅酸盐矿物高度不相容，因此模拟表明氮（以NH ₄ ⁺）在硅酸盐矿物中可以在变质脱挥发分过程中释放出来。俯冲地壳中大部分的氮可以在板坯脱挥发分过程中释放出来，并最终通过弧形岩浆脱气而排放到大气中。因此，与在扩散中心新形成的地壳相比，再循环到深地球的大洋地壳将消耗氮气。由于长期地幔对流，大块硅酸盐地球可能因俯冲而遭受了氮提取，这可能解释了地球大气中的氮富集。