From slab to surface: Earthquake evidence for fluid migration at Uturuncu volcano, Bolivia
From slab to surface: Earthquake evidence for fluid migration at Uturuncu volcano, Bolivia
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从板块到地表：玻利维亚乌图伦库火山流体迁移的地震证据
DOI：
10.1016/j.epsl.2021.117268
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发表时间：
2022
影响因子：
5.3
通讯作者：
Gottsmann, Joachim H.
中科院分区：
文献类型：
--
作者：
Hudson, Thomas S.;Kendall, J-Michael;Pritchard, Matthew E.;Blundy, Jonathan D.;Gottsmann, Joachim H.
乌图伦库火山位于玻利维亚安第斯山脉，直接位于世界上最大的地壳部分熔融体-高原-普纳岩浆体（APMB）之上。Uturuncu最后一次喷发是在25万年前，但地震活跃，位于直径70公里的隆起区中心。在这里，我们分析了2009年至2012年的地震活动。我们的地震位置，使用一个新开发的速度模型，划定的APMB的顶部和底部，揭示个别故障，并调和以前的研究之间的深度分布的差异。这些地震的空间聚类分析揭示了断层的方向，这与地震各向异性的应力方向相匹配。由矩震级得到的地震b值（1.44±0.06）与用当地震级测量得到的地震b值（0.80±0.03）有显著差异。从这些观察和理论的理由，我们建议，如果可能的话，力矩大小应用于准确的b值分析。我们解释b值> 1的流体增强地震活动。Uturuncu地区的浅层地震活动产生的b值> 1.1，并有一定的时间变化，表明流体沿着沿着浅层热液系统中预先存在的断层迁移，可能是由APMB的平流驱动的。有趣的是，比APMB更深的事件也产生了大的b值（1.4），映射了我们推断来自俯冲板片的流体上升到下地壳。累积起来，这些结果提供了一个活跃的岩浆系统的图片，在那里的流体交换更韧性APMB，喂养浅，断层控制的热液系统。这种流体上升通道可能影响我们对弧火山作用的认识，控制未来的火山喷发，并促进浅层热液矿床的积累。
Uturuncu volcano is situated in the Bolivian Andes, directly above the world's largest crustal body of silicic partial melt, the Altiplano-Puna Magma Body (APMB). Uturuncu last erupted 250,000 years ago, yet is seismically active and lies at the centre of a 70 km diameter uplifted region. Here, we analyse seismicity from 2009 to 2012. Our earthquake locations, using a newly developed velocity model, delineate the top and bottom of the APMB, reveal individual faults, and reconcile differences in depth distribution between previous studies. Spatial clustering analysis of these earthquakes reveals the orientations of the faults, which match stress orientations from seismic anisotropy. Earthquake b-values derived from moment magnitudes (1.44±0.06) differ significantly from those using local magnitude measurements (0.80±0.03). From these observations and theoretical justification, we suggest that, if possible, moment magnitudes should be used for accurate b-value analysis. We interpret b-values> 1 in terms of fluid-enhanced seismicity. Shallow seismicity local to Uturuncu yields b-values> 1.1 with some temporal variation, suggesting fluid migration along pre-existing faults in a shallow hydrothermal system, likely driven by advection from the APMB. Intriguingly, events deeper than the APMB also yield large b-values (1.4), mapping the ascent into the lower crust of fluids that we infer as originating from a subducting slab. Cumulatively, these results provide a picture of an active magmatic system, where fluids are exchanged across the more ductile APMB, feeding a shallow, fault-controlled hydrothermal system. Such pathways of fluid ascent may influence our understanding of arc volcanism, control future volcanic eruptions and promote the accumulation of shallow hydrothermal ore deposits.