Mechanisms influencing micron and nanometer-scale reaction rate patterns during dolostone dissolution

Emmanuel, Simon

doi:10.1016/j.chemgeo.2013.11.002

Cited by 40 publications

(46 citation statements)

References 31 publications

(43 reference statements)

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“…These values are reflective of the kinetic rate of dissolution, so that 1 represents the maximum rate of dissolution and 0 represents an inert state. In our formulation, grain boundaries dissolve 1 order of magnitude more rapidly than the mineral core, which is consistent with experimental work (Lüttge et al, 2013;Emmanuel, 2014;Bray et al, 2015).…”

Section: Modeling Rock Weatheringsupporting

confidence: 78%

Impact of grain size and rock composition on simulated rock weathering

Israeli¹,

Emmanuel²

2018

Earth Surf. Dynam.

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Abstract. Both chemical and mechanical processes act together to control the weathering rate of rocks. In rocks with micrometer size grains, enhanced dissolution at grain boundaries has been observed to cause the mechanical detachment of particles. However, it remains unclear how important this effect is in rocks with larger grains, and how the overall weathering rate is influenced by the proportion of high-and low-reactivity mineral phases. Here, we use a numerical model to assess the effect of grain size on chemical weathering and chemo-mechanical grain detachment. Our model shows that as grain size increases, the weathering rate initially decreases; however, beyond a critical size no significant decrease in the rate is observed. This transition occurs when the density of reactive boundaries is less than ∼ 20 % of the entire domain. In addition, we examined the weathering rates of rocks containing different proportions of high-and low-reactivity minerals. We found that as the proportion of low-reactivity minerals increases, the weathering rate decreases nonlinearly. These simulations indicate that for all compositions, grain detachment contributes more than 36 % to the overall weathering rate, with a maximum of ∼ 50 % when high-and low-reactivity minerals are equally abundant in the rock. This occurs because selective dissolution of the high-reactivity minerals creates large clusters of low-reactivity minerals, which then become detached. Our results demonstrate that the balance between chemical and mechanical processes can create complex and nonlinear relationships between the weathering rate and lithology.

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Section: Modeling Rock Weatheringsupporting

confidence: 78%

Impact of grain size and rock composition on simulated rock weathering

Israeli¹,

Emmanuel²

2018

Earth Surf. Dynam.

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“…Nevertheless, the spectral representation of rate maps ("rate spectra", [1]) does preserve the contribution of all surface features to the overall rate [25], and has seen limited but increasing adoption in the literature [12,17]. It can be clearly seen in Figure 5 that the spectra generated from calcite dissolution rate maps (see also Figure 4) are an asymmetric distribution, one that is consistent with a heterogeneous, Boltzmann distribution of reactive surface sites.…”

Section: Interpretation Of Reaction Mechanism Via Rate Spectral Analysismentioning

confidence: 74%

“…Several studies have recently indicated the fundamental variability of mineral surface rates, mainly due to the occurrence of heterogeneous reactive surface sites [1,12,37,38]. A detailed discussion on heterogeneity of mineral surfaces and its relationship with surface rate variability could be found in a recent review [25].…”

Section: Interpretation Of Reaction Mechanism Via Rate Spectral Analysismentioning

confidence: 99%

“…[5]). Both microscopes afford direct observation of mineral surfaces, and in situ AFM [6][7][8][9][10][11][12] and VSI [1,[13][14][15][16][17] have greatly expanded the understanding of reaction kinetics for a diverse range of carbonates, silicates, and other important phases. Calcite has been a favorite AFM and VSI target, due to its clear importance in environmental systems, its simple composition, and perfect cleavage.…”

Section: Introductionmentioning

confidence: 99%

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Temporal Evolution of Calcite Surface Dissolution Kinetics

et al. 2018

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Abstract:This brief paper presents a rare dataset: a set of quantitative, topographic measurements of a dissolving calcite crystal over a relatively large and fixed field of view (~400 µm 2 ) and long total reaction time (> 6 h). Using a vertical scanning interferometer and patented fluid flow cell, surface height maps of a dissolving calcite crystal were produced by periodically and repetitively removing reactant fluid, rapidly acquiring a height dataset, and returning the sample to a wetted, reacting state. These reaction-measurement cycles were accomplished without changing the crystal surface position relative to the instrument's optic axis, with an approximate frequency of one data acquisition per six minutes' reaction (~10/h). In the standard fashion, computed differences in surface height over time yield a detailed velocity map of the retreating surface as a function of time. This dataset thus constitutes a near-continuous record of reaction, and can be used to both understand the relationship between changes in the overall dissolution rate of the surface and the morphology of the surface itself, particularly the relationship of (a) large, persistent features (e.g., etch pits related to screw dislocations; (b) small, short-lived features (e.g., so-called pancake pits probably related to point defects); (c) complex features that reflect organization on a large scale over a long period of time (i.e., coalescent "super" steps), to surface normal retreat and step wave formation. Although roughly similar in frequency of observation to an in situ atomic force microscopy (AFM) fluid cell, this vertical scanning interferometry (VSI) method reveals details of the interaction of surface features over a significantly larger scale, yielding insight into the role of various components in terms of their contribution to the cumulative dissolution rate as a function of space and time.

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“…In addition to calculating the mean erosion rates, we used the kernel density estimation method (Vermeesch, 2012) to approximate the probability density functions for surface retreat (these functions are also called reaction rate spectra; Fischer et al, 2012;Lüttge et al, 2013;Emmanuel, 2014). Such a stochastic approach to reaction rates is likely to better represent the wide variability in geological materials, and may help to identify the mechanisms controlling the evolution of rock surfaces.…”

Section: Field Site and Lidar Scanningmentioning

confidence: 99%