Abstract
Fluid-rock interactions exert key control over rock rheology and strain localization. Redox may significantly affect the reaction pathways and, thereby, the mechanical properties of the rock. This effect may become critical in volatile-rich, redox sensitive rocks such as carbonate-rich lithologies, the breakdown of which can significantly modify the net volume change of fluid-mediated reactions. Subduction focus the largest recycling of crustal carbonates and the most intense seismic activity on Earth. Nevertheless, the feedbacks between deep carbon mobilization and deformation remain poorly investigated. We present quantitative microstructural results from natural samples and thermodynamic modeling indicating that percolation of reducing fluids exerts strong control on the mobilization of carbon and on strain localization in subducted carbonate rocks. Fluid-mediated carbonate reduction progressed from discrete domains unaffected by ductile deformation into localized shear zones deforming via diffusion creep, dissolution-precipitation creep and grain boundary sliding. Grain-size reduction and creep cavitation along localized shear zones enhanced fluid-carbonate interactions and fluid channelization. These results indicate that reduction of carbonate rocks can exert an important positive feedback on strain localization and fluid channelization, with potential implications on seismic activity and transport of deep hydrocarbon-bearing fluids.
Highlights
Fluid-rock interactions exert key control over rock rheology and strain localization
Field and microstructural observations indicate a strong correlation between the distribution of graphite, and thereby the degree of carbonate reduction, and the high-pressure, antigorite-bearing localized shear zones inside the rock
The collected data suggest that fluid-mediated reduction of carbonate rocks can favour strain localization at pressure and temperature conditions corresponding to the forearc region of subducted slabs
Summary
Fluid-rock interactions exert key control over rock rheology and strain localization. Grain-size reduction and creep cavitation along localized shear zones enhanced fluid-carbonate interactions and fluid channelization These results indicate that reduction of carbonate rocks can exert an important positive feedback on strain localization and fluid channelization, with potential implications on seismic activity and transport of deep hydrocarbon-bearing fluids. As fluid release drastically decreases the strength of a of rock volume (e.g.9 and references therein), and the destabilization of carbonate minerals may simultaneously decrease the volume of the rock and increase the amount of free fluid[4,10,11], redox-controlled mobilization of subducted carbonates[12,13] may potentially affect the rheology of deep rocks and cause mechanical instabilities at convergent margins. The interest towards reducing conditions relies on the fact that low fO2 can enhance carbonate decomposition and carbon mobility with respect to more oxidized conditions[8]
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