Volatile-consuming reactions fracture rocks and self-accelerate fluid flow in the lithosphere.
Proc Natl Acad Sci U S A 2022;
119:2110776118. [PMID:
35031568 PMCID:
PMC8784132 DOI:
10.1073/pnas.2110776118]
[Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/16/2021] [Indexed: 11/25/2022] Open
Abstract
Hydration and carbonation are the main reactions that drive volatile cycles in the Earth. These reactions are characterized by a large increase in solid volume, by up to several tens of percent, and may induce fracturing, fluid flow, and further reactions. However, no experimental studies have succeeded in a clear increase in fluid flow during the reactions, and the mechanisms that control acceleration or deceleration remain largely unknown. We present here clear experimental evidence that hydration reactions can fracture rocks and accelerate fluid flow, under confining pressure (i.e., at simulated depth). We conclude that a high reaction rate, relative to the fluid flow rate, is essential for fracturing and accelerated fluid flow during these reactions in the Earth.
Hydration and carbonation reactions within the Earth cause an increase in solid volume by up to several tens of vol%, which can induce stress and rock fracture. Observations of naturally hydrated and carbonated peridotite suggest that permeability and fluid flow are enhanced by reaction-induced fracturing. However, permeability enhancement during solid-volume–increasing reactions has not been achieved in the laboratory, and the mechanisms of reaction-accelerated fluid flow remain largely unknown. Here, we present experimental evidence of significant permeability enhancement by volume-increasing reactions under confining pressure. The hydromechanical behavior of hydration of sintered periclase [MgO + H2O → Mg(OH)2] depends mainly on the initial pore-fluid connectivity. Permeability increased by three orders of magnitude for low-connectivity samples, whereas it decreased by two orders of magnitude for high-connectivity samples. Permeability enhancement was caused by hierarchical fracturing of the reacting materials, whereas a decrease was associated with homogeneous pore clogging by the reaction products. These behaviors suggest that the fluid flow rate, relative to reaction rate, is the main control on hydromechanical evolution during volume-increasing reactions. We suggest that an extremely high reaction rate and low pore-fluid connectivity lead to local stress perturbations and are essential for reaction-induced fracturing and accelerated fluid flow during hydration/carbonation.
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