Pre- and syn-eruptive conditions of a basaltic Plinian eruption at Masaya Volcano, Nicaragua: The Masaya Triple Layer (2.1 ka)
Pre- and syn-eruptive conditions of a basaltic Plinian eruption at Masaya Volcano, Nicaragua: The Masaya Triple Layer (2.1 ka)
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DOI：
10.1016/j.jvolgeores.2019.106761
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发表时间：
2020-02-15
影响因子：
2.9
通讯作者：
Burton, Mike R.
中科院分区：
文献类型：
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作者：
Bamber, Emily C.;Arzilli, Fabio;Burton, Mike R.
马萨亚三层火山灰沉积于2100年前尼加拉瓜马萨亚破火山口的玄武质普林尼期喷发期间，是玄武质爆发火山作用极端端员的少数已知例子之一。马萨亚火山口距离尼加拉瓜首都马那瓜约25公里，普林尼火山爆发对其100万人口构成很高的潜在风险。在这里，我们使用地球化学和岩石学工具来约束喷发前和同喷发的物理化学岩浆条件，以了解低粘度玄武质岩浆如何以普林尼式喷发。通过结合温度模型和Rhyolite-MELTS模拟，我们发现马萨亚三重层岩浆最后储存在1080 - 1100摄氏度和21-42 MPa之间，具有类似于2wt%H2O的喷发前挥发物含量。一个小斑晶体积分数为0.1结晶水饱和条件下的浅岩浆水库位于0.8-1.6公里的深度。在上升过程中，发生快速微晶结晶和横向速度梯度横跨管道产生不同的结晶度，20和50体积%之间的异质混合区域。晶体粒度分布分析表明，大量的微晶结晶超过1-5分钟的时间尺度，这引起了显着的粘度和岩浆流变学的变化，在上升过程中，增加了有效的岩浆粘度从近似10帕秒至10（6）帕秒，并接近脆性碎裂阈值。已推导出的玄武质普林尼活动的其他例子，具有可比性的前和同喷发条件，表明一个共同的喷发机制。我们发现，共同的要求为玄武普林尼火山喷发是一个低的岩浆H2O浓度类似于2wt%，存储在1080-1100摄氏度的中等温度，并在岩浆上升过程中快速结晶。最终，这些条件促成了马萨亚这一高度危险的普林尼式火山爆发。(C)2020年，任作家。由爱思唯尔公司出版
The Masaya Triple Layer tephra was deposited -2100 years ago during a basaltic Plinian eruption of Masaya caldera, Nicaragua, and is one of few known examples of this extreme endmember of basaltic explosive volcanism. Masaya caldera is located approximately 25 km from Managua, the capital of Nicaragua, and a Plinian eruption presents a high potential risk to its population of 1 million people. Here we use geochemical and petrological tools to constrain the pre- and syn-eruptive physico-chemical magmatic conditions, in order to understand how low-viscosity basaltic magmas can erupt with Plinian style.By combining thermometric models with Rhyolite-MELTS simulations, we find that the Masaya Triple Layer magma was last stored between 1080 and 1100 degrees C and 21-42 MPa, with a pre-eruptive volatile content of similar to 2 wt% H2O. A small phenocryst volume fraction of 0.1 crystallised under water-saturated conditions within a shallow magma reservoir located at 0.8-1.6 km depth. During ascent, rapid microlite crystallisation occurred and lateral velocity gradients across the conduit produced heterogeneous inter-mingling regions of varying crystallinity, between 20 and 50 vol%. Crystal size distribution analysis shows substantial microlite crystallisation over a timescale of 1-5 min, which induced significant changes in viscosity and magma rheology during ascent, increasing the effective magma viscosity from similar to 10 Pa s to 10(6) Pa s and approaching the brittle fragmentation threshold. Comparable pre- and syn-eruptive conditions have been deduced for other examples of basaltic Plinian activity, indicating a common eruption mechanism. We find that the common requirements fora basaltic Plinian eruption arc a low magmatic H2O concentration of similar to 2 wt%, storage at moderate temperatures of 1080-1100 degrees C, and rapid crystallisation during magma ascent. Ultimately, these conditions contributed to the production of this highly hazardous Plinian eruption of Masaya. (C) 2020 The Authors. Published by Elsevier B.V.