加载、加热路径上橄榄石的相变及其对相变动力学参数计算的影响

本文研究了橄榄石原位相变实验中加载、加热路径上的相变及其对确定相变动力学参数的影响.利用文献［1］所给出的退火后先加温后加压，且相对低温条件下实验结果确定出的Ni₂SiO₄橄榄石相变动力学参数，计算了加载、加热路径上所发生的相变对确定成核率、长大率及相变体积分数的影响.结果表明，退火后先加压后加温，且相对高温条件下的实验数据受到加热路径上成核的影响.根据这样的实验数据得到的成核率会明显高于实际温压条件下的成核率.尤其是当多数实验都是高温实验时，根据这些成核率数据所确定的成核率参数会严重偏离其真值，从而严重影响对俯冲带颗粒粒度及俯冲带流变结构的计算.尽管目前有很多关于Mg₂SiO₄橄榄石长大率的实验数据，也有通过对挤碰物理图像的分析对(Mg_0.89Fe_0.11)₂SiO₄橄榄石成核率的估算，但只有文献［2］通过退火后先加压后加温的原位实验得到了Mg₂SiO₄橄榄石的相变成核率，且属于高温实验.根据本文的研究结果，我们认为亟需补充退火后先加温后加压或相对低温的实验数据以得到正确的地幔橄榄石成核率参数.

Nucleation on heating/loading path and its effects on the evaluation of nucleation rate

We investigate the nucleation on heating/loading path and its effects on the olivine phase transformation and the determination of nucleation rate in in-situ experiments, by the numerical simulation based on the kinetic parameters from low temperature experiments of Ni_2SiO_4 olivine phase transformation~(1]). Results show that the high temperature experiments, of which samples are first loaded then heated after annealing, are greatly affected by the nucleation during heating. The predicted nucleation rates based on such experiments are obviously overrated. Especially in the case that most experiments have high target temperatures, the predicted nucleation rates will significantly deviate from their true values, which has influence on the evaluation of the olivine grain size as well as the rheological structures of subduction zones. Although there are many growth data of Mg_2SiO_4 olivine and a rough evaluation on the nucleation rate of (Mg_(0.89) Fe_(0.11))_2 SiO_4 olivine based on the feature of the impingement, only Ref. 2] showed some nucleation rates of Mg_2SiO_4 olivine from high temperature in-situ experiments, in which the samples are finally heated to the target experimental condition. Our present study suggests that the experiments in low target temperature or those reached their experimental condition finally by loading are needed to derive the correct nucleation parameters of mantle olivine.