Opfergelt,S., Georg,R.B., Delvaux,B., Cabidoche,Y.-M., Burton,K.W. and Halliday,A.N.(2012): Silicon isotopes and the tracing of desilication in volcanic soil weathering sequences, Guadeloupe. Chemical Geology, 326-327, 113-122.

『グアドループの火山岩由来の土壌風化連続体におけるケイ素同位体と脱珪酸化の追跡』

『Abstract
　Silicon (Si) stable isotopes have the potential to become a useful weathering proxy, given that light Si isotopes are preferentially incorporated into secondary clay minerals. Here we investigate how Si depletion in soils and associated clay mineralogy influence the Si isotope fractionation associated with clay mineral formation. We report δ30Si compositions in bulk soils and clay fractions relative to their parent andesite in three soil weathering sequences from Guadeloupe that were formed under contrasting climatic conditions. Strongly desilicated soils containing kaolinite that formed in wet areas (high precipitation) are compared with less desilicated soils containing smectite formed in drier conditions (low precipitation). Clay fractions are isotopically lighter than the parent andesite (δ30Si-0.23‰), and increasingly lighter with Si depletion in soils, which supports the view that the Si isotope composition in secondary clay fractions is controlled by the degree of soil desilication. It is shown that the Si isotope fractionation factor between the parent silicate material and the secondary clay minerals is smaller for Si-rich secondary clay minerals such as smectite and larger for Si-poor secondary clay minerals such as kaolinite. This study provides new insights to better define Si isotopes as a proxy for environmental conditions for clay neoformation.

Keywords: Andesite weathering; Volcanic soils; desilication; Silicon isotopes; Guadeloupe』

1. Introduction
2. Environmental setting
3. Material and methods
　3.1. Sampling
　3.2. Soil characterisation
　3.3. Silicon isotope analysis
4. Results
　4.1. Soil weathering degree and desilication
　4.2. Silicon isotope signatures in soils and clay fractions
5. Discussion
　5.1. Potential controls on silicon isotope compositions of clay fractions
　　5.1.1. Clay content and soil desilication
　　5.1.2. Rainfall pattern and clay mineralogy
　　5.1.3. Isotope fractionation factors of clay minerals
　5.2. Contribution from atmospheric dust and biological cycling
　5.3. Implications
6. conclusions
Obituary for Dr. Yves-Marie Cabidoche
Acknowledgements
References

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