Effects of pressure and temperature on the silicon diffusivity of pyrope-rich garnet

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• 作者：Akira Shimojuku ; Tomoaki Kubo ; Takumi Kato ; Takashi Yoshino ; Masayuki Nishi ; Tomoki Nakamura ; Ryuji Okazaki ; Yuki Kakazu
• 关键词：Garnet ; Diffusion ; Rheology ; Mantle ; Subducted oceanic crust
• 刊名：Physics of the Earth and Planetary Interiors
• 出版年：January, 2014
• 年：2014
• 卷：226
• 期：Complete
• 页码：28-38
• 全文大小：1790 K

文摘

We have determined the pressure and temperature dependencies of Si volume diffusion rates in a single crystal of Pyp₇₅Alm₁₅Gr₁₀ garnet at 6-25 GPa and 1400-1800 掳C by the ²⁹Si tracer diffusion method. High-pressure experiments were conducted using the Kawai-type multi-anvil high-pressure apparatus. Diffusion profiles were obtained using secondary ion mass spectrometry in the depth-profiling mode. The Si diffusion coefficient in garnet (D_gt) is expressed by the Arrhenius equation: D_gt = D₀ exp(鈭?E^{鈭?/sup> + PV鈭?/sup>)/RT), with log₁₀D₀ = 鈭?.1 卤 1.7 m2/s, E鈭?/sup> = 345 卤 56 kJ/mol, and V鈭?/sup> = 4.7 卤 0.5 cm3/mol. Si diffusion seems to be the slowest in the major constituent elements in a pyrope-rich garnet and control rates of plastic deformation. The comparison between Si diffusion rates in garnet and wadsleyite/ringwoodite suggests that garnet has similar or slightly lower strength (at most 鈭? times) compared with wadsleyite, and has similar or slightly higher strength (at most 鈭? times) compared with ringwoodite at temperatures ranging from 900 to 1300 掳C. Thus, strength contrast between subducted oceanic crust and underlying peridotite layer may be small at the mantle transition zone conditions. This result suggests that the separation of subducted oceanic crust from an underlying peridotite layer may not occur.}