Pore-Scale Controls on Reaction-Driven Fracturing

Røyne, Anja; Jamtveit, Bjørn

doi:10.2138/rmg.2015.80.02

Cited by 42 publications

(31 citation statements)

References 80 publications

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“…The brown band thickens as the oxidation front migrates inward; micro‐cracks developed in the brown band and finally the surface portion of the brown band was exfoliated as a rindlet in our case. The development of the micro‐cracks may be facilitated by the precipitation of iron hydroxides fed with iron from dark aggregates in a same manner with the reaction‐induced fracturing (Røyne and Jamtveit, ). The thicknesses of the largest brown band and innermost rindlet varied in the range 1.5–6.0 cm and 2.2–6.0 cm, respectively, which suggests that rindlets exfoliated before the brown band became ~6 cm thick.…”

Section: Discussionmentioning

confidence: 99%

Spheroidal weathering of granite porphyry with well‐developed columnar joints by oxidation, iron precipitation, and rindlet exfoliation

Hirata

Chigira

Chen

2016

Earth Surf Processes Landf

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Spheroidal weathering, one of the important rock weathering styles, has been attributed to chemical weathering by the water from joint surfaces, and mechanical aspects of the weathering have not been well addressed. We made an investigation on spheroidal weathering of Miocene granite porphyry with well-developed columnar joints and found that this spheroidal weathering proceeds through chemical processes and accompanying mechanical processes. The investigation of the textures, physical properties, mineralogy, and chemistry of the porphyry revealed the presence of a brown band on the surface margins of corestones, representing the oxidation of pyrite and chlorite, and the precipitation of iron hydroxides, and the consequent generation of micro-cracks within the band. During weathering, oxidation progresses inwards from joints that surround the rindlets, including both high-angle columnar and low-angle planar joints, and causes rounding of the unweathered interior portion of the rock. Microscopic observations of the brown band embedded with fluorescent resin show that pores are first filled with iron hydroxides, and that micro-cracks then form parallel to the oxidation front in the outer portion of the brown band. Iron hydroxide precipitation increases the P-wave velocity in the brown band, while micro-crack formation decreases the tensile strength of the rock. Where the brown band has thickened to~6 cm, the micro-cracks are connected to one another to create continuous cracks, which separate the rindlets from the corestone. Micro-crack formation parallel to the corestone surface may be attributed to compressive stresses generated by small amounts of volumetric expansion due to the precipitation of iron hydroxides in the brown band. Earth surface is under oxidizing environments so that precipitation of iron hydroxides commonly occurs; the spheroidal weathering in this paper is a typical example of the combination of chemical and mechanical processes under such environments.

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Section: Discussionmentioning

confidence: 99%

Spheroidal weathering of granite porphyry with well‐developed columnar joints by oxidation, iron precipitation, and rindlet exfoliation

Hirata

Chigira

Chen

2016

Earth Surf Processes Landf

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“…While these coarse disciplinary divisions provide a tractable framework for understanding these complex processes, all of the factors intrinsic to chemical weathering likely coevolve as rock weathering proceeds. Despite the apparent importance of this coevolution, surprisingly few studies have provided a view of chemical weathering that connects the chemical, mechanical, and/or hydrologic properties of rock as it transforms to saprolite and soil [ Begonha and Sequeira Braga , ; Chigira et al ., ; Moon and Jayawardane , ; Fletcher et al ., ; Buss et al ., ; Røyne et al ., ; Røyne and Jamtveit , ].…”

Section: Introductionmentioning

confidence: 99%

The chemical, mechanical, and hydrological evolution of weathering granitoid

et al. 2016

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Surprisingly few studies connect the chemical, mechanical, and hydrological evolution of rock as it weathers to saprolite and soil. We assess this coevolution in granodiorite from Monterey Peninsula, California, by measuring changes in bulk chemistry, mineralogy, volumetric strain, the oxidation state of Fe in biotite crystals, tensile strength, abrasion rate, connected porosity, and hydraulic conductivity in samples covering a range of weathering grades. We identify the oxidative dissolution of biotite as the key chemical reaction because of the volumetric expansion that accompanies formation of altered biotite and precipitation of ferrihydrite. We show how the associated accumulation of elastic strain produces an energy density that is sufficient to support rock fracturing over length scales equivalent to constituent crystals. The resulting intragranular and intergranular cracking profoundly reduces tensile strength and increases the abrasion rate, connected porosity, and hydraulic conductivity of the rock matrix. These changes increase the rate of plagioclase weathering, and ultimately the rock disintegrates into grus and clay. Major changes in rock properties can occur with only minor element leaching, and the threshold behavior of weathering that arises from the coevolution of chemical, hydrological, and mechanical properties may be difficult to capture using simplified weathering models that fail to incorporate these properties. Our results, which combine the mechanical and hydrological evolution of weathering rock with more common measurements of chemical changes, should help to more accurately model the effects of, and mechanical and hydrological feedbacks upon, chemical weathering of rock.

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“…In 1985, Macdonald and Fyfe examined naturally altered peridotite and proposed that the large volume change associated with the reaction could generate high local stresses and strains, which would cause episodic cracking. This idea has then been applied to olivine carbonation by Kelemen and Matter (2008), who proposed a positive feedback loop where fractures could be generated during the volume-expanding reaction, porosity and permeability can be maintained or even increased, which in turn would accelerate the carbonation processes (Rudge et al, 2010). In 2011, Kelemen et al showed that in natural peridotites cross-cutting hierarchical fracture networks filled by synkinematic carbonate and quartz veins extend to microscopic scales.…”

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confidence: 99%

Generating porosity during olivine carbonation via dissolution channels and expansion cracks

et al. 2018

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Abstract. The olivine carbonation reaction, in which carbon dioxide is chemically incorporated to form carbonate, is central to the emerging carbon sequestration method using ultramafic rocks. The rate of this retrograde metamorphic reaction is controlled, in part, by the available reactive surface area: as the solid volume increases during carbonation, the feasibility of this method ultimately depends on the maintenance of porosity and the creation of new reactive surfaces. We conducted in situ dynamic X-ray microtomography and nanotomography experiments to image and quantify the porosity generation during olivine carbonation. We designed a sample setup that included a thick-walled cup (made of porous olivine aggregates with a mean grain size of either ∼ 5 or ∼ 80 µm) filled with loose olivine sands with grain sizes of 100–500 µm. The whole sample assembly was reacted with a NaHCO3 aqueous solution at 200 °C, under a constant confining pressure of 13 MPa and a pore pressure of 10 MPa. Using synchrotron-based X-ray microtomography, the three-dimensional (3-D) pore structure evolution of the carbonating olivine cup was documented until the olivine aggregates became disintegrated. The dynamic microtomography data show a volume reduction in olivine at the beginning of the reaction, indicating a vigorous dissolution process consistent with the disequilibrium reaction kinetics. In the olivine cup with a grain size of ∼ 80 µm (coarse-grained cup), dissolution planes developed within 30 h, before any precipitation was observed. In the experiment with the olivine cup of ∼ 5 µm mean grain size (fine-grained cup), idiomorphic magnesite crystals were observed on the surface of the olivine sands. The magnesite shows a near-constant growth throughout the experiment, suggesting that the reaction is self-sustained. Large fractures were generated as the reaction proceeded and eventually disintegrated the aggregate after 140 h. Detailed analysis show that these are expansion cracks caused by the volume mismatch in the cup walls, between the expanding interior and the near-surface which keeps a nearly constant volume. Nanotomography images of the reacted olivine cup reveal pervasive etch pits and wormholes in the olivine grains. We interpret this perforation of the solids to provide continuous fluid access, which is likely key to the complete carbonation observed in nature. Reactions proceeding through the formation of nano- to micron-scale dissolution channels provide a viable microscale mechanism in carbon sequestration practices. For the natural peridotite carbonation, a coupled mechanism of dissolution and reaction-induced fracturing should account for the observed self-sustainability of the reaction.

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Pore-Scale Controls on Reaction-Driven Fracturing

Cited by 42 publications

References 80 publications

Spheroidal weathering of granite porphyry with well‐developed columnar joints by oxidation, iron precipitation, and rindlet exfoliation

Spheroidal weathering of granite porphyry with well‐developed columnar joints by oxidation, iron precipitation, and rindlet exfoliation

The chemical, mechanical, and hydrological evolution of weathering granitoid

Generating porosity during olivine carbonation via dissolution channels and expansion cracks

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