Competition Between Crystallization‐Induced Expansion and Creep Compaction During Gypsum Formation, and Implications for Serpentinization

Abstract

Deformation caused by reaction‐driven volume increases is an important process in many geological settings. The interaction of rocks with reactive fluids can change permeability and reactive surface area, leading to a large variety of feedbacks. Gypsum (CaSO4·2H2O) is an ideal material to study these processes. It forms rapidly at room temperature via bassanite (CaSO4·[1/2]H2O) hydration and is commonly used as an analog for rocks in high‐temperature, high‐pressure conditions. We conducted uniaxial deformation experiments on porous bassanite aggregates to study the effects of applied axial load σa on deformation during the formation of gypsum. While hydration of bassanite involves a solid volume increase, gypsum exhibits significant creep compaction when in contact with water. These two processes occur simultaneously. Samples exhibited an initial phase of deformation followed by a slower secondary phase. A particular value of σa separates expansion from compaction during each of the deformation phases. At σa≤150 kPa, samples expanded initially; for σa≥230 kPa, samples compacted initially. Up to σa≈3.2 MPa, samples expanded after compacting initially, while for σa≥3.6 MPa, no further deformation or continued compaction occurred. This behavior implies that crystallization‐induced stresses depend on porosity and reaction extent such that larger stresses cannot be generated by the reaction. We explain aspects of the observed behavior with a model that predicts strain evolution using kinetic relationships for the reaction and creep rates and consider the implications of our results for reaction‐induced fracturing during serpentinization.

Phase‐Field Modeling of Reaction‐Driven Cracking: Determining Conditions for Extensive Olivine Serpentinization

“…Completely carbonated (listvenites) and hydrated (serpentinites) peridotites are, however, frequently observed in outcrops, Reaction-driven cracking has been observed in experiments involving both carbonation of olivine (Xing et al, 2018;Zhu et al, 2016) and hydration of magnesium oxide (Zheng et al, 2018). Other experiments on analogue systems have demonstrated that hydration reactions involving lime (Lambart et al, 2018;Wolterbeek et al, 2018) and bassanite (Skarbek et al, 2018) can produce significant crystallization-induced stresses. However, the conditions under which positive feedbacks (cracking) overcome negative feedbacks (clogging) remain relatively uncertain.…”

Modeling Porosity Evolution Throughout Reaction‐Induced Fracturing in Rocks With Implications for Serpentinization

“…As mentioned previously, it has been observed that the reaction rate decreases under large stress conditions (Skarbek et al, ; Wolterbeek et al, ; Zheng et al, ). Microstructural observations of Wolterbeek et al () indicated that reaction‐induced stresses shut down pathways for water into the sample, hampering ongoing reaction and limiting the magnitude of stress buildup to the values observed.…”

“…The modeling of serpentinization proposed in this study provides additional information compared to previous studies (Kelemen & Hirth, 2012;Skarbek et al, 2018). In the present study, serpentinization was…”

“…As mentioned previously, it has been observed that the reaction rate decreases under large stress conditions ( 2017) indicated that reaction-induced stresses shut down pathways for water into the sample, hampering ongoing reaction and limiting the magnitude of stress buildup to the values observed. Skarbek et al (2018) suggested that the stress limit could correspond to the strength of the material. During compaction, creep can occur, reducing the rate of reaction-induced fracturing.…”

Experimental Investigation of the Pressure of Crystallization of Ca(OH)2: Implications for the Reactive Cracking Process

“…As a result, there is no consensus regarding the nature of deformation due to retrograde metamorphism (e.g., Ghofrani & Plack, 1993;Kuleci et al, 2017;Ostapenko & Yaroshenko, 1975;Skarbek et al, 2018;Van Noort et al, 2017;Wolterbeek et al, 2017;Zhu et al, 2016). Generation of stress due to crystallization has been mostly studied in environments where crystallization occurs within a porous medium whose matrix does not participate in the reaction.…”