Exsolution of H2O, CO2, and S during eruptive episodes at Kilauea Volcano, Hawaii
Exsolution of H2O, CO2, and S during eruptive episodes at Kilauea Volcano, Hawaii
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夏威夷基拉韦厄火山喷发期间 H2O、CO2 和 S 的溶出
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发表时间：
1986
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影响因子：
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通讯作者：
T. Gerlach
中科院分区：
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作者：
T. Gerlach
当基拉韦厄岩浆从浅层地壳储层上升时，H2O、CO2和S从岩浆中析出的模型预测，只有当岩浆上升到浅深度（小于150米静岩），压力小于3兆帕（30巴）时，才会发生剧烈的析出。饱和状态下（30-100 MPa）的溶出蒸汽富含co2（最大70 vol %），但随着压力的下降，水蒸气中的H2O含量增加，最终占主导地位。然而，该模型表明，在低至2-3兆帕（20-30巴）的压力下，大多数水仍然溶解，而不是像通常假设的那样，在低于8兆帕（80巴）的压力下大量溶解。大多数CO2在10 MPa以上被溶解，而大多数S，如H2O，在2-3 MPa以下被溶解（< 100-150 m静岩）。在1.0 ~ 0.6 MPa （~ 40 ~ 25 m静岩力）时，达到了岩浆大规模脱气和破裂成喷雾的临界条件。气体溶解显然在中断后仍在继续。出溶模型预测的总挥发物析出量与火喷泉动力学模型预测的结果一致。在0.3 ~ 0.4 MPa（≤20 m）处，溶蚀气体与东部裂谷带喷发的火山气体相似，并与含有挥发物的熔体共存，其浓度与喷泉飞溅相似。从先前被破坏的熔体的聚结飞溅中析出会产生残余气体，这些气体富含h2o，并且在CO2中急剧减少。广泛溶解所需的低压和浅深度意味着岩浆必须被输送到接近地表的地方，才有可能发生破裂、脱气和涌出。因此，在基拉韦厄火山和其他拉斑玄武岩系统中，基于探测上升岩浆排出的挥发物的喷发预测技术可能无法提供有用的预警。
A model for the exsolution of H2O, CO2, and S from Kilauea magma as it rises from a shallow crustal reservoir predicts that vigorous exsolution occurs only after magma has ascended to shallow depths (≲ 150 m lithostatic) where pressures are <3 MPa (30 bars). Exsolved vapor at saturation (30–100 MPa) is CO2-rich (70 vol %, maximum), but H2O increases and ultimately predominates in the vapor as pressure drops. The model indicates that most H2O remains dissolved, however, down to pressures as low as 2–3 MPa (20–30 bars) rather than being exsolved abundantly below 8 MPa (80 bars) as is commonly assumed. Most CO2 is exsolved above 10 MPa, whereas most S, like H2O, is exsolved below 2–3 MPa (<100–150 m lithostatic). The critical condition for major outgassing and disruption of magma into spray is reached at 1.0–0.6 MPa (∼40–25 m lithostatic). Gas exsolution apparently continues after disruption. The total quantity of exsolved volatiles as predicted by the exsolution model agrees with that predicted by models of fire fountain dynamics. At 0.3–0.4 MPa (≲20 m lithostatic), the exsolved gases resemble volcanic gases of east rift zone eruptions and coexist with melts containing volatiles at concentrations similar to those observed in fountain spatter. Exsolution from coalesced spatter of previously disrupted melt produces residual gases that are H2O-rich and sharply depleted in CO2. The low pressures and shallow depths required for extensive exsolution imply that magma must be transported nearly to the surface before disruption, outgassing, and fountaining are possible. Therefore eruption forecasting techniques based on detection of volatiles outgassed from ascending magma may not provide useful advance warning at Kilauea and other tholeiite basalt systems.