Single-crystal elasticity of fayalite to 12 GPa
Single-crystal elasticity of fayalite to 12 GPa
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DOI：
10.1029/2004jb003162
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发表时间：
2004-12
影响因子：
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通讯作者：
S. Speziale;T. Duffy;R. Angel
中科院分区：
文献类型：
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作者：
S. Speziale;T. Duffy;R. Angel
[1]利用布里渊散射测量了天然富铁橄榄石(Fe0.94Mn0.06)2SiO4的单晶弹性常数。总体积模数、剪切模数和它们的压力导数分别为Ks0=136.3(2)Gpa、G0=51.2(2)Gpa、(∂KS/∂P)T0=4.9(1)、(∂G/∂P)0=1.8(1)和(∂2G/∂P2)0=−0.11(1)Gpa−1。括号中的数字是最后一位数的1个σ不确定度。结果表明，在常压和高压下，铁铝尖晶石的体相和剪切模量均与Fe/(Fe+Mg)比有关。体积弹性模量的压力导数对橄榄石中的铁含量非常敏感，而富镁和富铁组分的剪切弹性模量的压力依赖关系是相似的。在整个实验压力范围内，铁闪石的纵向(C11，C22，C33)和非对角(C12，C13，C23)模数与压力几乎呈线性关系。然而，剪切常数C44和C55在P>；5 GPa处表现出强烈的非线性压力依赖关系，比推算的铁沸石的室温稳定极限高2 Gpa以上。剪切常数的行为可能是在30~40 GPa时观察到的铁闪石高压非晶化的前兆。C44是显示出随压力软化的最强趋势的模数，这与先前的C55软化可能触发橄榄石向高压γ-Fe2SiO4结构转变的说法不一致。C44和C55的软化符合α-γ-Fe2SiO4结构的无扩散机制。
[1] Single-crystal elastic constants of a natural Fe-rich olivine (Fe0.94Mn0.06)2SiO4 were determined by Brillouin scattering to 12.1 GPa. The aggregate bulk modulus, shear modulus, and their pressure derivatives are KS0 = 136.3 (2) GPa, G0 = 51.2 (2) GPa, (∂KS/∂P)T0 = 4.9 (1), (∂G/∂P)0 = 1.8 (1), and (∂2G/∂P2)0 = −0.11 (1) GPa−1. The numbers in parentheses are 1σ uncertainties on the last digit. Our results demonstrate that both the bulk and the shear moduli of fayalite depend on the Fe/(Fe + Mg) ratio at both ambient and high pressures. The pressure derivative of the bulk modulus is very sensitive to the Fe content of olivine, while the pressure dependences of the shear modulus of Mg-rich and Fe-rich compositions are comparable. The longitudinal (C11, C22, C33) and the off-diagonal (C12, C13, C23) moduli of fayalite show a nearly linear dependence on pressure along the whole experimental pressure range. However, the shear constants C44 and C55 show a strongly nonlinear dependence on pressure starting at P > 5 GPa, more than 2 GPa above the extrapolated room temperature stability limit of fayalite. The behavior of the shear constants could be a precursor of the high-pressure amorphization of fayalite observed at 30 to 40 GPa. C44 is the modulus that shows the strongest tendency to soften with pressure, in disagreement with previous suggestions that C55 softening could trigger the structural transition of olivine to the high-pressure γ-Fe2SiO4. Softening of C44 and C55 is compatible with a diffusionless mechanism of the structural α- to γ-Fe2SiO4 transition.