Relationship between the Growth Rate of Forsterite Phase Transformation and Its Water Content and the Existing Depth of Metastable Olivine

详细信息   

• 责任者：Wang Shuguang (Institute of Earthquake Science ; China Earthquake Administration ; Beijing 100036 ; China) ; Liu Yajing
• 刊名：Chinese Journal of Geophysics
• 出版年：2011
• 卷期：54(7)
• 关键词：镁橄榄石 ; forsterite ; 俯冲带 ; subduction zones
• 页码：p.1758-1766
• 图表：5 illus., 3 tables, 30 refs.
• 分类号：0700
• 出版序号：1628
• issnNo：ISSN0001-5733
• isbnNo：CN11-2074/P

摘要

///The authors investigate the relatlonsntp uetween growth kinetics of forsterite phase transformation, i. e. , the pre-exponential factor and the Helmhotz free energy of activation, by analyzing the growth parameters of forsterite separately for water content varying from about 0.08 to 0.5 per cent in weight. Results show that increase of water content only decreases the Helmholtz free energy of activation for growth, while the preexponential factor of classical growth rate equation has weak dependence on the water content andis nearly a constant, of which the value corresponds to an interphase boundary with the thickness of one or a few layers of molecules. This fact is consistent with the observation of quench experiments on olivine and rheological studies. Accordingly, taking this fact as a constraint, we predict the survival depth of metastable forsterite with different water contents. The dynamic phase boundary of forsterite changes from several kilometers below the equilibrium boundary of forsterite phase transformation to almost the 660 km discontinuity. Different from forsterite, mantle olivine has smaller metastability. Under a nominal dry condition, the dynamic phase boundary of mantle olivine is 20 km shallower than that of forsterite. The current result agrees that there might exist detectable extent of metastable olivine in subduction zones although it is difficult to reach the 660-discontinuity.