2024-03-29T09:41:36Z
https://nagoya.repo.nii.ac.jp/oai
oai:nagoya.repo.nii.ac.jp:00031319
2023-01-16T04:24:53Z
367:1049:1050
Concentric Fe-oxyhydroxide bands in dacite cobbles: Rates of buffering chemical reactions
Yoshida, Hidekazu
103349
Katsuta, Nagayoshi
103350
Sirono, Sin-iti
103351
Nishimoto, Shoji
103352
Kawahara, Hirokazu
103353
Metcalfe, Richard
103354
Liesegang patterns
Fe-oxyhydroxide
Growth rate
pH buffering
‘Liesegang patterns’, rinds and bands are commonly observed in nature and form by self-organised periodic precipitation of Fe-oxyhydroxide following a nonlinear reaction-diffusion process. Although strictly Liesegang patterns consist of bands that increase in width with increasing distance from the source of the Fe that precipitated as Fe-oxyhydroxide, regular banded patterns are also sometimes observed that are otherwise similar to Liesegang patterns. However, the detailed process and time scale of regular Fe-oxyhydroxide bands development is still not fully understood. Here we describe an example of regular Fe-oxyhydroxide bands formed within dacite cobbles. Iron was provided to the outer surfaces of the cobbles by acidic water that diffused towards the cobbles' cores. The spatial distributions of Ca and Fe within the Fe-oxyhydroxide bands across the cobbles show that the rhythmic Fe-oxyhydroxide precipitation was controlled by pH buffering. The width of each band (L) and the expected diffusion coefficient of the rock matrix (D) provide the rate of reaction (V) and allow us to estimate the duration of Fe-oxyhydroxide band formation. A ‘diffusion-reaction cross plot’ implies that the rhythmic Fe-oxyhydroxide patterns formed very rapidly, within an order of 102–103 years, considerably faster than previously estimated. The simplified model can be applied to estimate the reaction time in any similar rock if regular Fe-oxyhydroxide bands are observed.
ファイル公開:2022-10-05
journal article
Elsevier
2020-10-05
application/pdf
Chemical Geology
552
119786
0009-2541
https://nagoya.repo.nii.ac.jp/record/31319/files/chemical_geology_552_119786.pdf
eng
https://doi.org/10.1016/j.chemgeo.2020.119786
© 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/