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Germanium isotopes and Ge_Si fractionation under extreme tropical weathering of basalts from the Hainan Island, South China
Hua-Wen Qi;  Rui-Zhong Hu;  Ke Jiang;  Ting Zhou;  Yue-Fu Liu;  Yan-Wen Xiong
2019
Source PublicationGeochimica et Cosmochimica Acta
Volume253Pages:249–266
Abstract
Chemical weathering of silicate rocks controls the flfluvial input of dissolved Ge and Si into the ocean, and has substantial inflfluence on the global Ge and Si geochemical cycles. The heavier dissolved Ge isotope compositions in the rivers (relative to the bulk silicate earth) suggest preferential incorporation of light isotopes into secondary weathering products during rock weathering (Baronas et al., 2017a). In this paper, we present the Ge isotope and Ge/Si ratio variations in the solid weathering products (soil and saprolite) from a well-developed basalt weathering profifile (>15 m thick, including soil, saprolite, semi
weathered rock and fresh basalt) on the tropical island of Hainan (South China). We discussed the elemental/isotopic fractionation mechanism and the possible inflfluence of major oxide composition on Ge isotope fractionation during extreme weathering of basalts in tropical climate. The Ge content ([Ge] = 2.19–4.12 ppm, 2.93 ppm on average, n = 52) and Ge/Si ratios (5.55–13.7 lmol/mol, 7.42 lmol/mol on average, n = 52) of solid weathering products are distinctly higher than those of the fresh basalts (avg. [Ge] = 1.64 ppm, Ge/Si = 2.66 lmol/mol, n = 5). The d74Ge values of solid weathering products range from 0.02 ± 0.10(2r) to 0.63 ± 0.10(2r), and exhibits complex stratigraphic variation across the weathering profifile. There are no distinct correlations between the concentrations of Ge (or the Ge/Si ratio and d74Ge values) and SiO2, Al2O3, Fe2O3 and MnO for most of the soil and saprolite samples. The distinct positive d74Ge vs. Ge (or sGe value and Ge/Si ratio) correlations for most soil and saprolite  samples indicate that the enrichment (or depletion) of Ge content, Ge isotopes and Ge/Si fractionation are controlled by a common sorption process of solid weathering products. The predicted opposite relationships between Ge/Si ratios and d74Ge values for pore water and that for solid weathering products can be evidenced by the positive Ge/Si vs. d74Ge correlation in the Wenchang basalt  weathering profifile and a negative one in the river water (Baronas et al., 2017a). Moreover, the estimated negative D74Gesolid-dissolved
(1000 * Ln(a)) value (1.38 ± 0.28(2r)) indicates that solid weathering products are a sink for light Ge isotopes, possibly balancing the  isotopic budget with heavy Ge isotope compositions in global rivers and oceans.
KeywordGe Isotopes Ge/si Ratio Chemical Weathering Basalt Hainan Island (South China)
Indexed BySCI
Language英语
Document Type期刊论文
Identifierhttp://ir.gyig.ac.cn/handle/42920512-1/10142
Collection矿床地球化学国家重点实验室
Affiliation1.State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
2.University of Chinese Academy of Sciences, Beijing 100049, China
Recommended Citation
GB/T 7714
Hua-Wen Qi;Rui-Zhong Hu;Ke Jiang;Ting Zhou;Yue-Fu Liu;Yan-Wen Xiong. Germanium isotopes and Ge_Si fractionation under extreme tropical weathering of basalts from the Hainan Island, South China[J]. Geochimica et Cosmochimica Acta,2019,253:249–266.
APA Hua-Wen Qi;Rui-Zhong Hu;Ke Jiang;Ting Zhou;Yue-Fu Liu;Yan-Wen Xiong.(2019).Germanium isotopes and Ge_Si fractionation under extreme tropical weathering of basalts from the Hainan Island, South China.Geochimica et Cosmochimica Acta,253,249–266.
MLA Hua-Wen Qi;Rui-Zhong Hu;Ke Jiang;Ting Zhou;Yue-Fu Liu;Yan-Wen Xiong."Germanium isotopes and Ge_Si fractionation under extreme tropical weathering of basalts from the Hainan Island, South China".Geochimica et Cosmochimica Acta 253(2019):249–266.
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