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

基于氮地球化学的地球大气-地幔系统演化研究.

基本信息

批准号：
07454138
负责人：
HIYAGON Hajime
金额：
$ 2.69万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

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.

为了了解基于氮的地球大气-地幔系统的演化，我进行了氮气和稀有气体在（A）气态硅酸盐熔体和（B）固体（cpx）-硅酸盐熔体之间的分配实验（A. ）在不同条件下进行：T=1300-1600ﾟC,P(N_2)=0.5-1000 atm f(O_2)=IW-2结果表明：（1）溶解氮浓度与P（N_2）呈线性相关（即遵循亨利定律），（2）氮溶解度（亨利常数）依赖性很弱。在温度 (3) 和 f(O_2) 上，并且大约等于 Ar 的所有这些观察结果表明氮在其中的物理溶解（即溶解为氮分子）。在目前的实验条件下，玄武岩熔体在^<15>N^<15>N富集氮和正常氮(^<14>N^<14>N-)之间几乎没有发生同位素交换。在实验（B）中，在高度氧化条件下合成的玄武岩熔体（玻璃）中溶解和提取氮的过程中，单斜辉石占主导地位）。 (cpx)-玄武岩熔体对在15kbar和1350-1270°C下使用活塞圆筒型装置合成。获得的cpx/熔体分配系数对于氮气为0.06，对于氩气为0.11，彼此没有显着差异。两个实验的结果表明，岩浆过程可能不会产生氮和氩之间的大分馏，因此，两个数量级的差异。大气(-10^4)和地幔(-10^6)的N/^<36>Ar比一定是岩浆作用以外的某些过程的结果。