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- Title
The Surface Deformation Signature of a Transcrustal, Crystal Mush‐Dominant Magma System.
- Authors
Mullet, Benjamin; Segall, Paul
- Abstract
The transcrustal, mush‐dominated magma storage paradigm, which posits liquid melt is heterogeneously distributed within a vertically extensive magma mush, differs significantly from classical geodetic models, where melt is stored within liquid‐dominant chambers within an elastic crust. Here, we present mechanical models consistent with transcrustal melt storage by separating the magmatic system into three domains: liquid melt lenses, surrounding crystal‐dominated poroelastic magma mush, and elastic crust. Our results indicate that pressure changes within the melt lens may induce surface displacements that approximate the displacements predicted by spheroidal pressure sources that mimic the geometry of the mush zone. Adopting constitutive parameters of the mush dependent on mush melt fraction, we show that a magma storage system will have an effective geometry inferred from surface displacements that smoothly transitions from the geometry of the melt lens to the geometry of the mush as mush melt fraction increases. This holds true across multiple storage zone geometries, including a "transcrustal" storage zone with a magma mush that extends deep in the crust. Accounting for the presence of a magma mush can lead to an increase in the estimated volume of injected or withdrawn magma (by several multiples) compared to values obtained using fully elastic models. Comparing erupted magma volumes to source volume changes allows for an estimation of magma compressibility; we show the presence of a mush can increase this estimated magma compressibility by up to approximately 50%, suggesting magmas may have higher bubble fraction than previous geodetically derived estimates. Plain Language Summary: Different kinds of geophysical observations provide differing views into the nature of magma storage regions within the crust. Many geophysical observations, such as seismic data, indicate that melt is stored within discrete, horizontally elongate pockets that are contained within a "mush" of solid crystals and liquid melt. However, surface deformations (geodetic data) are typically explained with models that ignore the presence of a magma mush. In this paper, we attempt to reconcile these views of magma storage regions, by incorporating the effects of a magma mush into models of ground deformation. Our results show that ground deformation measurements are potentially more sensitive to the magma mush than the discrete pockets of melt within the mush, and that appropriately accounting for the presence of a magma mush can change estimates of important quantities, such as the volume of injected magma and magma compressibility. Key Points: We develop a numerical poroelastic model for surface displacements induced by melt migration within a mush‐dominated melt storage regionSurface displacements may be more sensitive to the geometry of a low melt content mush than a melt‐rich lens within the mushAccounting for magma mush zones leads to important differences in estimation of quantities of interest, such as inferred volume change
- Subjects
DEFORMATION of surfaces; MAGMAS; LIQUID crystals; GEOPHYSICAL observations; CRYSTALS; URANIUM-lead dating; GOLD ores; DIAMOND crystals
- Publication
Journal of Geophysical Research. Solid Earth, 2022, Vol 127, Issue 5, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2022JB024178