H2O-CO2 solubility in alkali-rich mafic magmas: new experiments at mid-crustal pressures
H2O-CO2 solubility in alkali-rich mafic magmas: new experiments at mid-crustal pressures
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DOI：
10.1007/s00410-019-1592-4
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发表时间：
2019-07-01
影响因子：
3.5
通讯作者：
Clarke, Amanda B.
中科院分区：
文献类型：
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作者：
Allison, Chelsea M.;Roggensack, Kurt;Clarke, Amanda B.
岩浆中的挥发性溶解度取决于几个因素，包括成分和压力。具有高浓度碱性元素的镁铁质岩浆比亚碱性玄武岩能够溶解更大量的H2O和CO2，这可能有助于大爆发。现有的富碱镁铁质岩浆的挥发分溶解度模型在低于200 MPa时校准良好，但在更大的压力下，实验数据很少。为了填补这一空白，我们进行了一组混合H2O-CO2挥发物溶解度实验之间的400和600 MPa，在1200摄氏度的六个镁铁质组合物与可变碱含量（斯特龙博利，埃特纳，维苏威火山，埃里伯斯，日落火山口，和旧金山弗朗西斯科火山场）。从我们的实验结果表明，现有的富碱镁铁质岩浆的挥发性溶解度模型，如果外推超出其校准范围，不准确地描述中地壳压力下的CO2溶解度。我们适应现有的热力学模型，以反映我们的高压实验数据，通过确定模型参数Vr 0，m（CO2反应的偏摩尔体积变化）和K-0（平衡常数）为每个研究的组合物。在这些组合物中，Vr 0，m在15和25 cm（3）mol（-1）之间变化，而In K-0的范围为-14.9至-14.0。计算的溶解度曲线显示出良好的协议与CO2溶解度数据从实验中，并提供了一个更准确的描述CO2的溶解度比纯粹的经验拟合。这些新的实验表明，虽然CO2的溶解度增加，富碱镁铁质岩浆，它不是简单地控制总碱含量，而是完整的多组分岩浆组成。
Volatile solubility in magmas depends on several factors, including composition and pressure. Mafic magmas with high concentrations of alkali elements are capable of dissolving larger quantities of H2O and CO2 than subalkaline basalt, which possibly contributes to large explosive eruptions. Existing volatile solubility models for alkali-rich mafic magmas are well calibrated below similar to 200MPa, but at greater pressures the experimental data are sparse. To fill in this gap, we conducted a set of mixed H2O-CO2 volatile solubility experiments between 400 and 600MPa at 1200 degrees C in six mafic compositions with variable alkali contents (Stromboli, Etna, Vesuvius, Erebus, Sunset Crater, and the San Francisco Volcanic Field). Results from our experiments indicate that existing volatile solubility models for alkali-rich mafic magmas, if extrapolated beyond their calibrated ranges, do not accurately describe CO2 solubility at mid-crustal pressures. We adapt an existing thermodynamic model to reflect our higher-pressure experimental data by determining model parameters Vr0,m (partial molar volume change of CO2 reaction) and K-0 (equilibrium constant) for each studied composition. In these compositions, Vr0,m is found to vary between 15 and25cm(3)mol(-1), while ln K-0 ranges from - 14.9 to - 14.0. The calculated solubility curves show good agreement with CO2 solubility data from the experiments and provide a more accurate description of CO2 solubility than purely empirical fits. These new experiments indicate while CO2 solubility is increased in alkali-rich mafic magmas, it is not simply controlled by total alkali content but rather the full multicomponent magma composition.