Strain-induced magma degassing: insights from simple-shear experiments on bubble bearing melts
Strain-induced magma degassing: insights from simple-shear experiments on bubble bearing melts
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DOI：
10.1007/s00445-011-0471-2
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发表时间：
2011-04
影响因子：
3.5
通讯作者：
L. Caricchi;A. Pommier;M. Pistone;J. Castro;A. Burgisser;D. Perugini
中科院分区：
文献类型：
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作者：
L. Caricchi;A. Pommier;M. Pistone;J. Castro;A. Burgisser;D. Perugini
实验已经进行，以确定变形对含气泡熔体的脱气效果。初始含水量为1.5重量%的响岩成分圆柱形试样和2体积%气泡，已经在798-848 K的温度、100-180 MPa的围压和不同的最终应变下在内部加热的Paterson型压力容器中在简单剪切（扭转构型）中变形。使用光学显微镜、纳米层析成像机和同步加速器层析成像仪对变形前后的样品进行了二维和三维的微观结构分析。使用傅里叶变换红外光谱（FTIR）测量了变形前后玻璃的水含量。在总应变达到γ <$2的样品中，气泡准确地记录了总应变，而在更高的应变（γ <$10）下，气泡变得非常扁平，并在剪切方向上伸长。玻璃的残余水含量保持恒定，直到应变为γ_2，然后降低到约0.2wt.%在γ 10。结果表明，即使在低气泡体积分数下，应变也会增强气泡的聚并和脱气。值得注意的是，变形产生了强烈的水不饱和熔体。这表明，脱气可能发生在火山管道的很深处，并可能迫使岩浆在上升到地球表面的早期变得过冷，这可能有助于黑曜石的成因。
Experiments have been performed to determine the effect of deformation on degassing of bubble-bearing melts. Cylindrical specimens of phonolitic composition, initial water content of 1.5 wt.% and 2 vol.% bubbles, have been deformed in simple-shear (torsional configuration) in an internally heated Paterson-type pressure vessel at temperatures of 798–848 K, 100–180 MPa confining pressure and different final strains. Micro-structural analyses of the samples before and after deformation have been performed in two and three dimensions using optical microscopy, a nanotomography machine and synchrotron tomography. The water content of the glasses before and after deformation has been measured using Fourier Transform Infrared Spectroscopy (FTIR). In samples strained up to a total of γ ∼ 2 the bubbles record accurately the total strain, whereas at higher strains (γ ∼ 10) the bubbles become very flattened and elongate in the direction of shear. The residual water content of the glasses remains constant up to a strain of γ ∼ 2 and then decreases to about 0.2 wt.% at γ ∼ 10. Results show that strain enhances bubble coalescence and degassing even at low bubble volume-fractions. Noticeably, deformation produced a strongly water under-saturated melt. This suggests that degassing may occur at great depths in the volcanic conduit and may force the magma to become super-cooled early during ascent to the Earth’s surface potentially contributing to the genesis of obsidian.