VOLATILE OVERSATURATION DURING THE EVOLUTION OF SILICIC MAGMA CHAMBERS AS AN ERUPTION TRIGGER
VOLATILE OVERSATURATION DURING THE EVOLUTION OF SILICIC MAGMA CHAMBERS AS AN ERUPTION TRIGGER
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DOI：
10.1029/jb089ib10p08237
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发表时间：
1984-01-01
影响因子：
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通讯作者：
BLAKE, S
中科院分区：
文献类型：
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作者：
BLAKE, S
大而浅的岩浆房显然可以产生自己的潜力，启动破火山口产生喷发。最初贫水的硅质岩浆的分异在岩浆房顶部产生了一个稳定的分级带，该区域由温度低、结晶度低、含水量高的极度分级的低密度液体组成。在这种系统的长期演化之后，岩浆房中最上面的岩浆将在水中变得过饱和，产生超压。通过在高于稳定岩石静力学值的压力下使岩浆和岩浆房体积相等，可以将这种过量的岩浆压力评估为岩浆的可压缩性、水含量和溶解度、岩石静力学压力（岩浆房深度）和一些假定的岩浆房膨胀能力的测量值的函数。据信5至25 MPa之间的临界超压足以使大多数岩浆室破裂，这意味着对于850°C的流纹岩岩浆，埋藏在1.5-7 km深度的岩浆室的临界含水量在3- 6wt%范围内。过饱和层中岩浆的泡状度被计算为0.1%，但在过饱和层是岩浆房的一小部分（小于百分之几）的情况下，当岩浆房在压力增加时会膨胀时，泡状度可能达到0.10%。从这项研究中得出的结论是，在浅深度演化的分馏岩浆不能达到远高于6或7重量%的含水量，因为这样做，它们变得过饱和，并最终喷发。
Large, shallow silicic magma chambers can apparently generate their own potential to initiate caldera‐producing eruptions. Differentiation of an initially water‐poor siliceous magma yields a stably graded zone of extremely fractionated low‐density liquids of low temperature, low crystallinity, and high water content at the chamber top, After protracted evolution of such a system, the uppermost magma in the chamber will become oversaturated in water, generating an excess pressure. By equating the magma and chamber volumes at some pressure above the stable lithostatic value, this excess magmatic pressure can be evaluated as a function of the magma's compressibility, water content and solubility, lithostatic pressure (chamber depth), and some assumed measure of the chamber's ability to expand. Critical overpressures between 5 and 25 MPa are believed to be sufficient to rupture most chambers, implying that for rhyolite magma at 850°C, the critical water contents are in the range 3–6 wt % for chambers buried at depths of 1.5–7 km. The vesicularities of the magma in the oversaturated layer are calculated to be ≲1% but may reach ∼10% in cases where the oversaturated layer is a small (less than a few percent) part of the chamber and when the chamber can dilate during the increase in pressure. It follows from this study that fractionated magmas evolving at shallow depth cannot attain water contents much above 6 or 7 wt %, since in so doing they become oversaturated and are ultimately erupted.