Thermal diffusivity of Fe-rich pyroxene glasses and their melts
Thermal diffusivity of Fe-rich pyroxene glasses and their melts
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DOI：
10.1016/j.chemgeo.2014.06.018
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发表时间：
2014-09
期刊：
影响因子：
3.9
通讯作者：
A. Hofmeister;A. Sehlke;A. Whittington
中科院分区：
文献类型：
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作者：
A. Hofmeister;A. Sehlke;A. Whittington
我们提供了8个合成玻璃和熔体沿顽火辉石-铁硅石成分二元、4个接近二元的重熔晶体和一个合成三元成分(Fs15Wo40En45)的热扩散系数(D)的新测量结果。这些玻璃的热扩散系数在室温下为0.50-0.62mm2s−-1，在1000K附近降至~0.45-0.50mm2s-−-1，然后在1100K熔融时下降到~0.34mm2s-−-1。298K时，整个EN-F二元系的D值大致呈线性趋势，富Fe组分较低，而在高温下，所有熔体的D值相似。这一趋势并不平坦，这是因为玻璃中的微晶和残余应变的数量不同，这两者都会影响D值。在约700K以上，∂D/∂Ti对中等Fe含量(即Fe+Fe+Fe-Mg)呈明显的正值，我们将其归因于电子-振动耦合增强了扩散辐射传输。所有数据都很好地用FT−、G和H的形式表示，其中F、G和H是拟合参数。拟合显示，我们所有的玻璃的Dat High T都有微弱的增加，这与红外辐射的微弱传输是一致的。虽然只能在很窄的温度范围内收集熔体的数据，但它们的∂D/∂T似乎也是正的，这与之前对含铁较少的玻璃和熔体的结果一致。我们的结果表明，由于D对温度的响应，下地幔富铁熔体的热扩散率可能比它们的晶态熔体高。
We provide new measurements of thermal diffusivity (D) of 8 synthetic glasses and melts along the enstatite–ferrosilite compositional binary, 4 remelted crystals which are close to the binary, plus one synthetic ternary composition (Fs15Wo40En45). Thermal diffusivity of these glasses is between 0.50 and 0.62 mm2s− 1at room temperature, decreases to ~ 0.45 to 0.50 mm2s− 1near 1000 K, then drops upon melting at 1100 K to ~ 0.34 mm2s− 1. A roughly linear trend inDexists across the En–Fs binary at 298 K, with Fe-rich compositions having lowerD, whereas at high temperatures all melts have similarD. The trend is not smooth, due to variable amounts of crystallites and residual strain in glasses, both of which affectD-values. Above about 700 K, ∂D/∂Tis visibly positive for moderate Fe contents (i.e., Fe / (Fe + Mg) = 0.1 to 0.3), which we attribute to diffusive radiative transfer being enhanced by electronic–vibronic coupling. All data are well represented by equations of the form FT− G+ HT, where F, G and H are fitting parameters. The fitting reveals a weak increase inDat highTfor all of our glasses, consistent with weak radiative transfer in the infrared. Although data could only be collected on melts over a narrow temperature range, they also appear to have a positive ∂D/∂T, which is consistent with previous results on less mafic iron-bearing glasses and melts. Our results suggest that Fe-rich melts in the lower mantle could have thermal diffusivity higher than their crystalline counterparts due to the response ofDto temperature.