Magma Reservoir Below Laguna del Maule Volcanic Field, Chile, Imaged With Surface‐Wave Tomography
Magma Reservoir Below Laguna del Maule Volcanic Field, Chile, Imaged With Surface‐Wave Tomography
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DOI：
10.1029/2018jb016485
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发表时间：
2019-03
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通讯作者：
C. Wespestad;C. Thurber;N. Andersen;B. Singer;C. Cardona;Xiangfang Zeng;N. Bennington;K. Keranen;D. Peterson;Darcy Cordell;M. Unsworth;C. Miller;G. Williams-Jones
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作者：
C. Wespestad;C. Thurber;N. Andersen;B. Singer;C. Cardona;Xiangfang Zeng;N. Bennington;K. Keranen;D. Peterson;Darcy Cordell;M. Unsworth;C. Miller;G. Williams-Jones
莫莱湖（LdM）火山区包含了安第斯山脉中最大规模的冰后期流纹岩，包括约40立方千米的爆发式和溢流式喷发产物。近年来，通过干涉合成孔径雷达和全球导航卫星系统大地测量在莫莱湖的观测发现，自2007年以来，其膨胀速率超过20厘米/年，这捕捉到了一个潜在的大型上地壳岩浆库正在增长的时期。此外，大地电磁和重力研究表明，在膨胀中心附近的上地壳中存在流体和/或部分熔融物。岩石学观测表明，至少在过去2.6万年里，流纹岩熔体从储存在4 - 6千米深处的晶粥中反复快速提取。我们利用多种类型的面波观测来约束莫莱湖下方低速区域的位置和几何形状。我们提出了一个三维横波速度模型，该模型描绘了一个位于地表以下约2 - 8千米、体积约为450立方千米的浅部岩浆库，其平均熔体分数约为5%。结合现有的重力、大地电磁和大地测量观测对地震层析成像进行解释，支持了这一模型，并比任何单一的地球物理方法都更详细地揭示了熔体含量的变化以及为浅部岩浆库提供物质的更深部岩浆系统。如今对莫莱湖岩浆系统的地球物理成像与过去2 - 6万年里对岩浆库结构和增长的岩石学推断是一致的。结合当前的动荡情况，未来发生至少与全新世常见规模相当的流纹岩喷发是一种合理的可能性。
The Laguna del Maule (LdM) volcanic field comprises the greatest concentration of postglacial rhyolite in the Andes and includes the products of ~40 km3 of explosive and effusive eruptions. Recent observations at LdM by interferometric synthetic aperture radar and global navigation satellite system geodesy have revealed inflation at rates exceeding 20 cm/year since 2007, capturing an ongoing period of growth of a potentially large upper crustal magma reservoir. Moreover, magnetotelluric and gravity studies indicate the presence of fluids and/or partial melt in the upper crust near the center of inflation. Petrologic observations imply repeated, rapid extraction of rhyolitic melt from crystal mush stored at depths of 4–6 km during at least the past 26 ka. We utilize multiple types of surface‐wave observations to constrain the location and geometry of low‐velocity domains beneath LdM. We present a three‐dimensional shear‐wave velocity model that delineates a ~450‐km3 shallow magma reservoir ~2 to 8 km below surface with an average melt fraction of ~5%. Interpretation of the seismic tomography in light of existing gravity, magnetotelluric, and geodetic observations supports this model and reveals variations in melt content and a deeper magma system feeding the shallow reservoir in greater detail than any of the geophysical methods alone. Geophysical imaging of the LdM magma system today is consistent with the petrologic inferences of the reservoir structure and growth during the past 20–60 kyr. Taken together with the ongoing unrest, a future rhyolite eruption of at least the scale of those common during the Holocene is a reasonable possibility.