Impact of grain size and rock composition on simulated rock weathering
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...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-05-01
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| Series: | Earth Surface Dynamics |
| Online Access: | https://www.earth-surf-dynam.net/6/319/2018/esurf-6-319-2018.pdf |
| Summary: | 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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| ISSN: | 2196-6311 2196-632X |