A study on evolultion of the Earth's atmosphere-mantle system based on nitrogen geochemistry.

为了了解基于氮的地球大气-地幔系统的演化，我在(A)气态硅酸盐熔体和(B)固体（cpx）硅酸盐熔体之间进行了氮和惰性气体的pertitioning实验。实验(A)在不同条件下进行：T=1300 ~ 1600‰，P(N_2)=0.5 ~ 1000‰，f(O_2)=IW-2 ~ IW+10（对数标度）。结果表明：(1)溶氮浓度与P（N_2）呈线性相关。(2)氮的溶解度（亨利常数）对温度(3)和f（O_2）的依赖性非常弱，与Ar的溶解度近似相等。所有这些观察结果表明，在目前的实验条件下，氮在玄武岩熔体中的物理溶解（即以氮分子的形式溶解）。在高氧化条件下合成的玄武岩熔融体（玻璃）中，氮的溶解和提取过程中，几乎没有发生^<15>N^<15>N富集氮和正常氮（^<14>N^<14>N为主）之间的同位素交换。实验(B)采用活塞-柱式装置，在15kbar和1350-1270苯甲酸的条件下合成了斜硝石(cpx)-玄武岩熔体对。得到的cpx/熔体分配系数在氮气为0.06，氩气为0.11，两者差异不显著。这两个实验的结果暗示岩浆过程可能不会在氮和氩之间产生大的分馏。因此，大气（-10^4）和地幔（-10^6）的N/^<36>比值的两个数量级差异一定是岩浆作用以外的其他作用的结果。

In order to understand the evolition of the Earth's atmosphere-mantle system based on nitrogen, I conducted experiments on pertitioning of nitrogen and noble gases between (A) gas-silicate melt and (B) soild (cpx)-silicate melt. Experiment (A) was conducted under various conditions : T=1300-1600ﾟC,P(N_2)=0.5-1000 atm f(O_2)=IW-2 to IW+10 (logarithmic scale). The results show that (1) concentration of dissolved nitrogen is linearly correlated with P(N_2)(i.e., Henry's Law is obeyed), (2)nitrogen solubility (Henry's constant) has very weak dependence on temperature (3) and on f(O_2), and is approximately equal to that of Ar. All these observations suggest physical dissolution of nitrogen (i.e., dissolution as nitrogen molecules) in basaltic melt in the present experimental conditions. This is also suppoeted by the observation that almost no isotopic exchange occured between ^<15>N^<15>N-enriched nitrogen and normal nitrogen (^<14>N^<14>N-dominated) during dissolution nd extraction of nitrogen in and from the basaltic melt (glass) synthesized under a highly oxydizing condition. In experiment (B), a clinopyroxene (cpx)-basaltic melt pair wes synthesized using a piston-cylinder-type apparatus at 15kbar and 1350-1270ﾟC.The obtainned cpx/melt partition coefficients are 0.06 for nitrogen and 0.11 for argon, not significantly different with each other. The results of the two experiments imply that magmatic processes may not produce large fractionation between nitrogen and argon. Therefore, the two orders of magnitude difference in the N/^<36> Ar ratios of the atmosphere (-10^4) and the mantle (-10^6) must be the result of some processes other than the magmatic ones.