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Nitrogen solubility in basaltic silicate melt - Implications for degassing processes
Chemical Geology ( IF 3.9 ) Pub Date : 2021-03-24 , DOI: 10.1016/j.chemgeo.2021.120192
Fabien Bernadou , Fabrice Gaillard , Evelyn Füri , Yves Marrocchi , Aneta Slodczyk

The distribution of nitrogen between the different terrestrial reservoirs (core-mantle-atmosphere) and how this may have changed since the earliest planetary stages is uncertain. In particular, the primordial degassing processes of the magma ocean and its role in the formation of the atmosphere remains to be quantified. Since no geological samples can capture this early degassing process, we need to go through the thermodynamic modeling of the nitrogen solubility in silicate melt. We hence performed experiments on basaltic samples at fluid saturation in the C-H-O-N system, using an Internally Heated Pressure Vessel (IHPV) and Piston Cylinder (PC) in the pressure range 0.8 kbar to 10 kbar, temperature between 1200 and 1300 °C, and a wide range of fO2 conditions from IW + 4.9 to IW-4.7 (IW standing for the Iron-Wustite redox buffer). The nitrogen concentration in the quenched silicate melts at fluid saturation was analysed by secondary ion mass spectrometry (SIMS), and the speciation of the dissolved C-O-H species was determined by Fourier transform infrared spectroscopy (FTIR). We identified two nitrogen species in the silicate melt: N2 dominating at fO2 > IW and N3− at lower fO2. Using these data and a database constraining nitrogen concentration at fluid saturation from 1 bar to 10 kbar pressure, we calibrated a solubility law for nitrogen in basalts defining its P-T-fO2 dependences. This model expands the model of Libourel et al. (2003) to high pressure and higher C-O-H activities. It can be used to investigate the nitrogen degassing processes for different pressure, temperature and fO2 conditions relevant to planetary accretion and modern volcanism.



中文翻译:

氮在玄武质硅酸盐熔体中的溶解度-对脱气过程的意义

目前尚不确定不同地球储层(核心-地幔-大气层)之间的氮分布以及自最早行星阶段以来氮如何变化。特别是,岩浆海洋的原始脱气过程及其在大气形成中的作用仍有待量化。由于没有地质样品能够捕获这种早期的脱气过程,因此我们需要对氮在硅酸盐熔体中的溶解度进行热力学建模。因此,我们使用压力为0.8 kbar至10 kbar,温度为1200至1300°C的内部加热压力容器(IHPV)和活塞缸(PC)在CHON系统中处于饱和流体状态下的玄武岩样品上进行了实验。广泛的fO 2条件从IW + 4.9到IW-4.7(IW代表铁-韦氏体氧化还原缓冲液)。通过二次离子质谱(SIMS)分析了流体饱和时淬火的硅酸盐熔体中的氮浓度,并通过傅里叶变换红外光谱(FTIR)确定了溶解的COH物种的形态。我们在硅酸盐熔体中确定了两个氮物种:在fO 2  > IW时占主导地位的N 2和在较低fO 2时占优势的N 3−。使用这些数据和一个将流体饱和度从1 bar压缩到10 kbar时限制氮浓度的数据库,我们校准了定义其PT-fO 2的玄武岩中氮的溶解度定律。依赖。该模型扩展了Libourel等人的模型。(2003年)到高压和较高的COH活动。它可用于研究与行星增生和现代火山作用有关的不同压力,温度和fO 2条件下的氮气脱气过程。

更新日期:2021-04-09
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