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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Volatile degassing, petrology, and magma dynamics of the Villarrica Lava Lake, Southern Chile
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Volatile degassing, petrology, and magma dynamics of the Villarrica Lava Lake, Southern Chile

机译：智利南部比利亚里卡熔岩湖的挥发性脱气，岩石学和岩浆动力学

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摘要

Villarrica is a 2847-m-high, subduction zone stratovolcano located in the southern Chilean Andes (39.5°S). This volcano has been characterized by continuous, open-vent, passive degassing from a summit lava lake, with negligible eruption of magmatic material, from the end of the last eruption in 1985 to the time of writing. The major- and trace-element bulk composition of Villarrica magma (basaltic andesite) has been identical from 1984 to the present. Samples of Villarrica magma from the lava lake contain 33 wt.% plagioclase (An_(58-74)), 7 wt.% olivine (Fo_(75-78)), and trace amounts of chromian spinel. Glass inclusions in olivine and plagioclase are basaltic andesite in composition, are mostly degassed, and contain 30-440 ppm S, 170-360 ppm Cl, 340-600 ppm F, 0.1 +- 0.6 wt.% H_2O, and 20-70 ppm CO-2. One gas-rich glass inclusion contains 920 ppm S, 530 ppm Cl, and 1.4 wt.% H_2O. Matrix glasses are basaltic andesite and contain 80-150 ppm S, 190-250 ppm Cl, 440-630 ppm F, and 0.0 +- 0.7 wt.% H_2O. MELTS modeling suggests that all crystallization occurred at P < 170 bar, T = 1130-1140℃, f_(O_2) = NNO under water-saturated conditions. The upper bound for the initial amount of dissolved H_2O in Villarrica melt is unconstrained. In 2001, Villarrica emitted 460 +- 260 tons/day SO_2, 102 +- 42 tons/day HCl, and 13 +- 3 tons/day HF. On average, ～ 2.2 m~3/s of magma is degassed (or 5800 kg/s) which implies ～ 1.2 km~3 of magma has degassed since 1985. Intrusion of 1.2 km~3 of degassed magma into the volcanic edifice would cause > 50 m of vertical deformation, but there is no visible bulging of the edifice or mass wasting of the cone caused by deformation-induced gravitational instability. Instead, convection of magma in a volcanic conduit with ～ 5 m diameter is the most likely mechanism for transporting both the volatiles and heat to produce the observed gas emissions and prevent the lava lake from solidifying.
机译：比利亚里卡（Villarrica）是2847米高的俯冲带平流火山，位于智利安第斯山脉南部（39.5°S）。从1985年最后一次喷发结束到本文写作之时，这座火山的特征是从山顶熔岩湖进行连续，开放式的被动脱气，岩浆物质的喷发量可忽略不计。 1984年至今，维拉里卡岩浆（玄武质安山岩）的主要和微量元素的总体组成是相同的。来自熔岩湖的比利亚里卡岩浆样品含有33 wt。％斜长石（An_（58-74）），7 wt。％橄榄石（Fo_（75-78））和痕量的铬尖晶石。橄榄石和斜长石中的玻璃夹杂物成分为玄武质安山岩，大部分已脱气，并且包含30-440 ppm S，170-360 ppm Cl，340-600 ppm F，0.1±-0.6 wt。％H_2O和20-70 ppm CO-2。一种富含气体的玻璃夹杂物包含920 ppm S，530 ppm Cl和1.4 wt。％H_2O。基质玻璃是玄武质安山岩，并且包含80-150 ppm S，190-250 ppm Cl，440-630 ppm F和0.0±0.7 wt。％H_2O。 MELTS模型表明，所有结晶都发生在水饱和条件下的P <170 bar，T = 1130-1140℃，f_（O_2）= NNO。 Villarrica熔体中初始溶解H_2O量的上限不受限制。 2001年，比利亚里卡排放了460±260吨/天的SO_2、102±42吨/天的HCl和13±3吨/天的HF。平均而言，对〜2.2 m〜3 / s的岩浆进行了脱气（或5800 kg / s），这意味着自1985年以来，已经对〜1.2 km〜3的岩浆进行了脱气。将1.2 km〜3的经脱气的岩浆侵入火山大厦将导致> 50 m的垂直变形，但没有因变形引起的重力不稳定性而导致的建筑物的凸起或圆锥体的质量浪费。取而代之的是，直径约5 m的火山管道中的岩浆对流是传输挥发物和热量以产生观测到的气体排放并阻止熔岩湖凝固的最可能机制。

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