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- Title
Decompaction Weakening as a Mechanism of Fluid Focusing in Hydrothermal Systems.
- Authors
Utkin, Ivan; Afanasyev, Andrey
- Abstract
We present a mathematical model of nonreactive fluid flow in a compacting porous medium. The model differs from previous formulations by considering fluid transport in the frame of reference moving with the solid phase. Such an approach guarantees material balance for the fluid and solid phases not only in the small‐porosity limit but also for large values of porosity. Using the numerical implementation of the proposed model, we simulate magmatic fluid transport in the Earth's upper crust. We account for the thermal softening of rocks, the plastic deformation of the solid matrix through decompaction weakening, and realistic fluid properties in a wide range of depths, including those above and below the brittle‐ductile transition (BDT). We show that our simulation approach can resolve the localized flow in the ductile zone and numerous hydrothermal convection cells in the brittle zone. We investigate the influence of decompaction weakening on high‐porosity channels forming in the ductile zone and their interaction with the convection in the brittle zone. We show that compaction causes magmatic fluid focusing and accumulation in high‐porosity lenses beneath the low‐porosity BDT zone. We show that magmatic fluid transfer through the BDT occurs mainly through the roofs of the lenses, which results in a plume of hydrothermal convection always sitting atop every lens. Other plumes between the lenses are associated with the convection of meteoric water that transfers only heat from the BDT to the surface. The simulations indicate that the lenses can be tracked by measuring certain parameters at the surface. Plain Language Summary: Magma cooling and degassing cause large volumes of hot water to exsolve. We investigate the flow of this magmatic fluid to the Earth's surface through permeable rocks. We account for complicated deformations of rocks and associated pore space closing and opening, that is, compaction and decompaction, which causes a spontaneous channelization of the flow at large depths. These channels interact with the meteoric water convection in the Earth's uppermost crust. We simulate this interaction and show that the magmatic fluid focuses and accumulates in high‐porosity lenses at a shallow depth. Most of the fluid flows through these lenses and escapes to the surface through their roofs. Thus, the lenses can be associated with regions of ore deposit formation. Above the lenses, the magmatic fluid mixes with the meteoric water, causing a convective plume of ascending water to sit above each lens. Therefore, the magmatic fluid reaches the surface in narrow areas that can be associated with hot springs. Key Points: We simulate magmatic fluid transport above, below, and through the brittle‐ductile transition (BDT)Interaction with meteoric convection causes fluid focusing below the BDT in high‐porosity lensesMagmatic fluid transport through BDT occurs mainly through the roofs of the lenses
- Subjects
FLUID flow; MATHEMATICAL models; POROUS materials; DEGASSING of metals; POROSITY
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 9, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB022397