Mixed‐Mode Strain Localization Generated by Hydration Reaction at Crustal Conditions. Issue 5 (15th May 2019)

• Record Type: Journal Article
• Authors: Zheng, Xiaojiao; Cordonnier, Benoît; McBeck, Jessica; Boller, Elodie; Jamtveit, Bjørn; Zhu, Wenlu; Renard, François
• Is Part Of: Journal of geophysical research. Volume 124:Issue 5(2019)
• Page Start: 4507
• Page End: 4522
• Publication Date: 2019-05-15
• Subjects: reaction‐induced fracturing -- retrograde metamorphism -- serpentinization -- digital volume correlation; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2018JB017008
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Hydration reactions influence rock density and rheology. For example, volume increases produced in hydration reactions may generate sufficient tensile and shear stress to fracture both the rock undergoing the reaction and the surrounding host rock. We performed in situ dynamic X‐ray synchrotron microtomography experiments to investigate reaction‐induced fracturing. Two experiments on hydration of periclase were performed at 180 or 190 °C, under a confinement of 10 or 80 MPa, a pore fluid pressure of 5 or 75 MPa, and with or without differential stress. The sample assembly consists of a periclase cylinder inserted into a central hole within a serpentinite cylinder. The reaction from periclase to brucite results in a large volume increase (110%), pushing the periclase/brucite against the serpentinite and ultimately breaking it. Using time‐resolved three‐dimensional imaging, we quantify the spatial and temporal distribution of the reaction‐induced fractures. We perform digital volume correlation analysis to obtain the incremental strain tensors throughout the hydration and fracturing process. We use numerical models to assess the distribution of stress within the serpentinite. The digital volume correlation results show mixed‐mode strain localization. The von Mises strain, indicative of shear, increases by a larger percentage than the contractive or dilatative strain components as the reaction‐induced fractures grow. The distribution of von Mises strain follows a power law relationship in the cumulative frequency‐magnitude domain, indicative of long‐range elastic stress interactions during fracturing. This experimental finding sheds insights on the mechanisms of microseismicity measured in areas undergoing active serpentinization. Key Points: Reaction‐induced fracturing of periclase produces self‐sustained hydration to brucite The hydration reaction generates sufficient tensile stress to fracture a confining serpentinite cylinder Strain localization in the serpentinite includes both tensile and shear components with a power law distribution of shear strain magnitudes