Rheology of fine‐grained forsterite aggregate at deep upper mantle conditions
Rheology of fine‐grained forsterite aggregate at deep upper mantle conditions
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DOI：
10.1002/2013jb010473
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发表时间：
2014-01
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通讯作者：
Yu Nishihara;T. Ohuchi;T. Kawazoe;D. Spengler;M. Tasaka;T. Kikegawa;A. Suzuki;E. Ohtani
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文献类型：
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作者：
Yu Nishihara;T. Ohuchi;T. Kawazoe;D. Spengler;M. Tasaka;T. Kikegawa;A. Suzuki;E. Ohtani
对细粒合成纯橄榄石（镁橄榄石集合体）进行高压和高温变形实验，以确定上地幔深处的主要变形机制。烧结原材料含有 90% 镁橄榄石、10% 顽辉石，平均晶粒尺寸约为 1 µm。变形实验是在干燥环境<50 H/106Si、压力为3.03–5.36 GPa、温度为1473–1573 K、单轴应变率为0.91 × 10−5 至18.6 × 10−5 s−1 的条件下使用变形-DIA 装置进行的。在每个变形条件下确定稳态流动应力。使用扩散蠕变（应力指数 n = 1，晶粒尺寸指数 p = 2）和位错适应晶界滑动（GBS-disl，n = 3，p = 1）的流动定律方程，对导出的应力应变率数据与类似但低压变形实验报告的数据进行分析。纯铜岩扩散蠕变 (V*dif) 和 GBS-disl (V*GBS) 的活化体积分别确定为 8.2 ± 0.9 和 7.5 ± 1.0 cm3/mol。基于这些结果的计算表明，在地球软流圈上地幔典型变形条件下，扩散蠕变和位错蠕变对物质流动起着重要作用，而GBS-disl的贡献非常有限，并且位错蠕变是剪切橄榄岩捕虏体中橄榄石变形过程中的主要变形机制。尽管这些结论并不明确，但这是基于压力、温度、应力和晶粒尺寸空间外推的镁橄榄石骨料潜在变形机制的第一个结果。
High‐pressure and high‐temperature deformation experiments on fine‐grained synthetic dunite (forsterite aggregate) were conducted to determine the dominant deformation mechanism in the deep upper mantle. The sintered starting material has 90% forsterite, 10% enstatite, and an average grain size of ~1 µm. Deformation experiments were performed using a deformation‐DIA apparatus at pressures of 3.03–5.36 GPa, temperatures of 1473–1573 K, and uniaxial strain rates of 0.91 × 10−5 to 18.6 × 10−5 s−1 at dry circumstances <50 H/106Si. The steady state flow stress was determined at each deformation condition. Derived stress‐strain rate data is analyzed together with that reported from similar but low‐pressure deformation experiments using flow law equations for diffusion creep (stress exponent of n = 1, grain‐size exponent of p = 2) and for dislocation‐accommodated grain‐boundary sliding (GBS‐disl, n = 3, p = 1). The activation volume for diffusion creep (V*dif) and for GBS‐disl (V*GBS) of dunite is determined to be 8.2 ± 0.9 and 7.5 ± 1.0 cm3/mol, respectively. Calculations based on these results suggest that both diffusion creep and dislocation creep play an important role for material flow at typical deformation conditions in the Earth's asthenospheric upper mantle whereas the contribution of GBS‐disl is very limited, and dislocation creep is the dominant deformation mechanism during the deformation of olivine in sheared peridotite xenolith. Though these conclusions are not definitive, these are the first results on potential deformation mechanisms of forsterite aggregate based on extrapolation in the pressure, temperature, stress, and grain‐size space.