Rheological Controls on Magma Reservoir Failure in a Thermo-Viscoelastic Crust
Rheological Controls on Magma Reservoir Failure in a Thermo-Viscoelastic Crust
复制标题
热粘弹性地壳中岩浆库破坏的流变控制
DOI：
10.1029/2021jb023439
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发表时间：
2022
期刊：
影响因子：
3.4
通讯作者：
Head M
中科院分区：
文献类型：
--
作者：
Head M
由于火山经历动荡，了解岩浆库失败所需的条件和时间尺度，以及与大地测量观测的联系，在评估岩浆迁移到地表和喷发的可能性时至关重要。从表面变形事件推断加压岩浆系统的动力学在很大程度上依赖于假设的地壳流变学，通常由弹性介质表示。在这里，我们使用有限元模型来识别温度依赖的标准线性固体粘弹性（“热粘弹性”）域中对储层加压的流变响应。我们通过评估沿储层壁沿着发生脆性破坏所需的超压以及对关键参数的敏感性来评估变形储层的机械稳定性。由于地壳粘度不均匀，储层膨胀促进了韧性围岩的压缩，影响了诱导张应力的时间演化。与弹性分析相比，热粘弹性使变形储层能够在失效前承受更大的超压。高温（例如，镁铁质）储层在与低温相比更低的超压下失效（例如，长英质）储层，在地表产生较小的重合位移。热粘弹性对储层破坏的影响在很宽的超压加载速率范围内是显著的。通过抵抗储层壁上的机械破坏，热粘弹性影响岩脉成核和剪切裂缝的形成。数值模型可能需要纳入促进故障的其他过程，例如区域应力（例如，地形和构造），外部触发（例如，地震应力下降），或沿水库壁沿着预先存在的弱点。
As volcanoes undergo unrest, understanding the conditions and timescales required for magma reservoir failure, and the links to geodetic observations, are critical when evaluating the potential for magma migration to the surface and eruption. Inferring the dynamics of a pressurized magmatic system from episodes of surface deformation is heavily reliant on the assumed crustal rheology, typically represented by an elastic medium. Here, we use Finite Element models to identify the rheological response to reservoir pressurization within a temperature‐dependent Standard Linear Solid viscoelastic (“thermo‐viscoelastic”) domain. We assess the mechanical stability of a deforming reservoir by evaluating the overpressures required to initiate brittle failure along the reservoir wall, and the sensitivity to key parameters. Reservoir inflation facilitates compression of the ductile wall rock, due to the non‐uniform crustal viscosity, impacting the temporal evolution of the induced tensile stress. Thermo‐viscoelasticity enables a deforming reservoir to sustain greater overpressures prior to failure, compared to elastic analyses. High‐temperature (e.g., mafic) reservoirs fail at lower overpressures compared to low‐temperature (e.g., felsic) reservoirs, producing smaller coincident displacements at the ground surface. The impact of thermo‐viscoelasticity on reservoir failure is significant across a wide range of overpressure loading rates. By resisting mechanical failure on the reservoir wall, thermo‐viscoelasticity impacts dyke nucleation and formation of shear fractures. Numerical models may need to incorporate additional processes that act to promote failure, such as regional stresses (e.g., topographic and tectonic), external triggers (e.g., earthquake stress drops), or pre‐existing weaknesses along the reservoir wall.