Vertically Extensive Magma Reservoir Revealed From Joint Inversion and Quantitative Interpretation of Seismic and Gravity Data
Vertically Extensive Magma Reservoir Revealed From Joint Inversion and Quantitative Interpretation of Seismic and Gravity Data
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DOI：
10.1029/2019jb018476
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发表时间：
2019-11
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影响因子：
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通讯作者：
M. Paulatto;M. Moorkamp;S. Hautmann;E. Hooft;J. Morgan;R. Sparks
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作者：
M. Paulatto;M. Moorkamp;S. Hautmann;E. Hooft;J. Morgan;R. Sparks
我们对弧岩浆系统认识的最新进展表明，熔体在低熔点晶体糊中储存了很长时间，而可喷发的岩浆库寿命很短，并且通过浮力引起的不稳定性和晶体糊的排水而迅速聚集。它们的结构的许多方面仍不清楚，特别是与它们的几何形状和浅熔体分布有关的方面。我们利用联合地球物理反演与基于岩石物理学的定量解释方法相结合，研究了蒙特塞拉特岛苏弗里耶尔山活火山 (SHV) 下面的熔体储存情况。我们联合反演主动源 P 波走时和重力异常，得出 8 km 深度的 P 波速度和密度的一致 3D 模型。对活跃的 SHV 和中心山死火山的比较分析以及有效的弹性介质计算使我们能够限制温度、熔体分数和熔体几何形状。据推测，SHV 下方 4-8 公里深处有一个连续的部分熔融柱。熔体分数约为 6%（根据熔体几何形状，范围为 3% 至 13%），并且在 5-6 km 深度处达到最大值。当考虑到低 vP 体积的回收不足时，熔体分数修正为约 17%（范围从 11% 到 28%）。 vP/密度交会图分析表明，低纵横比几何形状可以最好地表示熔体分布。这些可能跨越多尺度范围，从颗粒尺度的包裹体和裂缝到 100 米尺度的堤坝和基台。我们的结果证实了垂直延伸的晶体糊状物的概念，包括一个或多个富含熔体的层。
Recent advances in our understanding of arc magmatic systems indicate that melt is stored for long periods in low‐melt fraction crystal mushes and that eruptible magma reservoirs are short‐lived and are assembled rapidly by buoyancy‐induced instabilities and draining of the crystal mush. Many aspects of their architecture remain unclear, particularly in relation to their geometry and shallow melt distribution. We investigate the storage of melt below the active Soufrière Hills Volcano (SHV), Montserrat, using joint geophysical inversion combined with a quantitative interpretation approach based on rock physics. We jointly inverted active‐source P‐wave traveltimes and gravity anomalies to derive coincident 3‐D models of P‐wave velocity and density to a depth of 8 km. Comparative analysis of the active SHV and extinct Centre Hills volcano and effective elastic medium computations allow us to constrain temperature, melt fraction, and melt geometry. A continuous column of partial melt is inferred beneath SHV, at 4–8 km depth. Melt fraction is ~6% (ranging from 3 to 13% depending on melt geometry) and is maximum at 5–6 km depth. When under‐recovery of the low‐vP volume is taken into account, the melt fraction is revised to ~17% (ranging from 11 to 28%). Analysis of vP/density cross plots indicates that the melt distribution is best represented by low‐aspect ratio geometries. These likely span a multiscale spectrum ranging from grain‐scale inclusions and fractures to 100‐m‐scale dykes and sills. Our results confirm the concept of vertically extensive crystal mush including one or multiple more melt‐rich layers.