Causes of unrest at silicic calderas in the East African Rift: New constraints from InSAR and soil-gas chemistry at Aluto volcano, Ethiopia
Causes of unrest at silicic calderas in the East African Rift: New constraints from InSAR and soil-gas chemistry at Aluto volcano, Ethiopia
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东非大裂谷硅质破火山口动荡的原因：埃塞俄比亚阿鲁托火山 InSAR 和土壤-气体化学的新限制
DOI：
10.1002/2016gc006395
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Hutchison W
中科院分区：
文献类型：
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作者：
Hutchison W
无休止的硅质火山口存在着重大的地质灾害，但许多火山口也拥有大量未开发的地热资源。在东非，这构成了一个重大挑战，尽管火山口基本上不受监测，但其地热资源可为该地区带来可观的经济利益。了解是什么导致了这些火山的动荡，对于权衡机会和潜在风险至关重要。在这里，我们将新的实地和遥感观测结合在一起，以评估位于埃塞俄比亚主要裂谷(MER)中的一座永不停歇的硅质火山Aluto的地面变形原因。干涉合成孔径雷达(InSAR)数据揭示了2008至2010年间发生的一次地表形变事件的时间和空间特征。形变时间序列揭示了加速隆升向逐渐长期下沉过渡的脉冲，分析模型支持∼5公里的膨胀源深度。沿着阿卢托主要断裂带逃逸的气体显示出高的CO2通量和明显的岩浆碳特征(CO2-δ13C of−4.2‰至−4.5‰)。这提供了令人信服的证据，表明该杂岩的岩浆和热液储集层在物理上是相连的。我们认为，岩浆-热液耦合系统可以解释隆升-沉陷信号。我们假设岩浆储集层盖层中的岩浆流体注入和/或侵入驱动了整个建筑物的膨胀，而随后的收缩与岩浆脱气和热液系统的降压有关。这些对阿卢托管道的新限制，为了解裂谷火山系统的行为提供了重要的见解，并将对解释未来的动荡模式至关重要。
Restless silicic calderas present major geological hazards, and yet many also host significant untapped geothermal resources. In East Africa, this poses a major challenge, although the calderas are largely unmonitored their geothermal resources could provide substantial economic benefits to the region. Understanding what causes unrest at these volcanoes is vital for weighing up the opportunities against the potential risks. Here we bring together new field and remote sensing observations to evaluate causes of ground deformation at Aluto, a restless silicic volcano located in the Main Ethiopian Rift (MER). Interferometric Synthetic Aperture Radar (InSAR) data reveal the temporal and spatial characteristics of a ground deformation episode that took place between 2008 and 2010. Deformation time series reveal pulses of accelerating uplift that transition to gradual long‐term subsidence, and analytical models support inflation source depths of ∼5 km. Gases escaping along the major fault zone of Aluto show high CO2flux, and a clear magmatic carbon signature (CO2‐δ13C of −4.2‰ to −4.5‰). This provides compelling evidence that the magmatic and hydrothermal reservoirs of the complex are physically connected. We suggest that a coupled magmatic‐hydrothermal system can explain the uplift‐subsidence signals. We hypothesize that magmatic fluid injection and/or intrusion in the cap of the magmatic reservoir drives edifice‐wide inflation while subsequent deflation is related to magmatic degassing and depressurization of the hydrothermal system. These new constraints on the plumbing of Aluto yield important insights into the behavior of rift volcanic systems and will be crucial for interpreting future patterns of unrest.