Negative activation volume of oxygen self-diffusion in forsterite
Negative activation volume of oxygen self-diffusion in forsterite
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DOI：
10.1016/j.pepi.2017.12.005
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发表时间：
2018-02-01
影响因子：
2.3
通讯作者：
Katsura, Tomoo
中科院分区：
文献类型：
--
作者：
Fei, Hongzhan;Wiedenbeck, Michael;Katsura, Tomoo
用Kawai型多面顶压机和常压炉测量了干法合成无铁橄榄石(镁橄榄石)单晶在1600K和10(-4)~13 Gpa压力下的氧自扩散系数(D-Ox)。采用二次离子质谱仪进行深度剖析，获得扩散谱。镁橄榄岩中的DO随压力的增加而增加，其活化体积为-3.9+/-1.2 cm(3)/mol。虽然在低压条件下，镁橄榄岩中镁的扩散速度最快，但在压力大于10 Gpa时，0的扩散速度最快。在镁橄榄岩的稳定压力范围内，Si是最慢的。根据观测到的D-Ox和D-Mg(镁自扩散系数)的正负压力关系，镁橄榄岩中的D-Ox+D-Mg随压力的增加而减小，然后在压力大于10 Gpa时略有增加。这一行为与基于电导率测量的镁橄榄岩中离子电导率的压力依赖关系是一致的(Yoshino等人，2017)，并可以用来解释从类似于300公里深到软流圈底部的电导率增加。
Oxygen self-diffusion coefficients (D-Ox) were measured in single crystals of dry synthetic iron-free olivine (forsterite, Mg2SiO4) at a temperature of 1600 K and under pressures in the range 10(-4) to 13 GPa, using a Kawai-type multi-anvil apparatus and an ambient pressure furnace. Diffusion profiles were obtained by secondary ion mass spectrometry operating in depth profiling mode. Do in forsterite increases with increasing pressure with an activation volume of -3.9 +/- 1.2 cm(3)/mol. Although Mg is the fastest diffusing species in forsterite under low-pressure conditions, 0 is the fastest diffusing species at pressures greater than similar to 10 GPa. Si is the slowest throughout the stable pressure range of forsterite. Based on the observed positive and negative pressure dependence of D-Ox and D-Mg (Mg self-diffusion coefficient), respectively, D-ox + D-Mg in forsterite decreases with increasing pressure, and then increases slightly at pressures greater than 10 GPa. This behavior is in agreement with the pressure dependence of ionic conductivity in forsterite based on conductivity measurements (Yoshino et al., 2017), and can be used to explain the conductivity increase from similar to 300 km depth to the bottom of the asthenosphere.