Surface tension and bubble nucleation in phonolite magmas
Surface tension and bubble nucleation in phonolite magmas
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声浪石岩浆中的表面张力和气泡成核
DOI：
10.1016/j.gca.2011.10.017
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发表时间：
2012
影响因子：
5
通讯作者：
J. Gardner
中科院分区：
文献类型：
--
作者：
J. Gardner
爆炸性的普林尼火山喷发利用了广泛的岩浆成分，包括高碱性响岩岩浆。这种喷发是由从岩浆中逸出的挥发物驱动的，因此确定气泡是如何形成的对于理解这些喷发很重要。硅酸盐熔体中气泡的成核强烈地取决于熔体的表面张力（σ），因此本研究的重点是确定响岩熔体的σ。以富钠响岩为芯的粘土矿物水化率为5.37±0.09wt.%在150 MPa和1150°C下溶解水，然后在1150°C或875°C下减压。在1150°C时，只有当压力降到95 MPa以下时，气泡才成核，数密度为104-5cm−3。在875°C时，气泡只有在压力低于53 MPa时才成核，数密度为104- 7 cm −3。根据临界气泡核内的压力是否等于饱和压力或可变的较低压力，观察到的数密度和成核速率意味着富钠响岩的表面张力在875°C时为0.061或0.068Nm− 1，在1150°C时为0.052或0.066Nm− 1。重要的是，温度对σ的影响很小或轻微的负面影响，与流纹岩熔体对σ的热影响相反。不管压力假设，推断的表面张力表明，富钠响岩可以成为高度过饱和的水之前，气泡成核，这可能会导致他们爆炸性脱气和喷发，类似于高粘性流纹岩。
Explosive Plinian eruptions tap a wide range of magma compositions, including highly alkaline phonolite magma. Such eruptions are driven by volatiles exsolving from those magmas, and so determining how gas bubbles form is important to understanding those eruptions. Nucleation of bubbles in silicate melts is dictated strongly by the surface tension (σ) of the melt, and so this study focuses on determining σ for phonolite melts. Cylinders cored from a sodium-rich phonolite were hydrated with 5.37±0.09wt.% dissolved water at 150MPa and 1150°C, and then decompressed at either 1150°C or 875°C. Bubbles nucleated at 1150°C only when pressure dropped below 95MPa, in number densities of 104–5cm−3. At 875°C bubbles nucleated only when pressure dropped below 53MPa, in number densities of 104–7cm−3. Depending on whether the pressure within critical bubble nuclei equals the saturation pressure or a variable lower pressure, the observed number densities and nucleation rates imply that surface tension for Na-rich phonolite is 0.061 or 0.068Nm−1at 875°C and 0.052 or 0.066Nm−1at 1150°C. Importantly, temperature has little or slightly negative impact on σ, in contrast to the thermal impact on σ of rhyolite melts. Regardless of pressure assumption, the inferred surface tensions indicate that Na-rich phonolite can become highly super-saturated with water before bubbles nucleate, which could cause them to explosively degas and erupt, similar to highly viscous rhyolites.