摘要：
Oceanic subduction zones are important channels for carbon exchange between the Earth's crust and mantle. However, the nature of carbon cycles at depths from 120 to 410 km in the subduction zone remains unknown. To decipher this issue, high-precision stable Mg isotopes of arc-like volcanic rocks from Tengchong, Southwestern China, have been investigated. The Tengchong volcanic rocks comprise basalts and andesites, with Mg0 content varying from 2.41 to 8.48 wt.%. Both the basalts and andesites exhibit homogeneous and light Mg isotopic compositions with delta Mg-26 ranging from -0.51 to -0.45 parts per thousand and -0.49 to -0.33 parts per thousand, respectively. Their delta Mg-26 values are lower than the average mantle (delta Mg-26 = -0.25 +/- 0.07 parts per thousand) and island arc lavas (delta Mg-26 = -0.35 to +0.06%e), but similar to the <110 Ma intra-continental basalts from eastern China (delta Mg-26 = -0.60 to 0.30 parts per thousand). This light Mg isotopic composition could not originate from the accumulation of ilmenite in their mantle source because both the Nb/Ta and delta Mg-26 values of the basalts are invariant with TiO2 content. The recycling of carbonated eclogites is also unlikely because of the lack of any correlation between delta Mg-26 and either (Gd/Yb)(N) or Fe/Mn ratios in the Tengchong basalts. Alternatively, the most probable explanation for the light Mg isotopic composition is the recycling of sedimentary carbonates in the mantle source. This is supported by the high Na2O + K2O/TiO2 ratios (3.3-4.1), low Ti/Ti* and Hf/Hf* values in the basalts, which are consistent with the partial melting trend of carbonated peridotite. Additionally, the high Ba/Th, low Rb/Cs and enriched Sr-Nd isotopes (EMII-like endmember) of the Tengchong basalts indicate the presence of Indian sediments in their mantle source. Furthermore, the extremely high Th/U (6.5-8.3) ratios in basalts suggest the higher mobility of Th than U, which is a unique characteristic of slab-derived supercritical liquids in subduction zones with pressures greater than 6 GPa. Based on the quantitative modeling of Mg-Sr-Nd-Pb isotopes and trace elements, the mantle source of the Tengchong basalts lies along mixing lines of the DMM with 1% supercritical liquids and 15-19% recycled mixture containing 66-72% dolomite, 22-26% calcite and 2-12% Indian sediments. Given that the recycled mixture is mainly dolomite (66-72%), we proposed that the slab-derived supercritical liquids can dissolve dolomite and then metasomatized the overlying mantle to form carbonated peridotite. Partial melting of this mantle source should be located at a depth of similar to 120 to 300 km under which supercritical liquids can occur, which is supported by seismic tomographic observations. The Tengchong andesites display many geochemical features similar to the basalts, such as enrichments in LILEs (Large Ion Lithophile Elements), LREEs (Light Rare Earth Elements) and Sr-Nd-Pb isotopes, as well as low delta Mg-26 values, suggesting a petrogenetic link between these two rock types. Our detailed study suggests that the andesites evolved from the Tengchong basalts via assimilation and fractional crystallization (AFC) processes. This interpretation is also supported by the geophysical tomography, which reveals a low-velocity anomalous zone in the continental crust. This study reveals a new carbon cycle in which Mg-rich carbonate - dolomite - can be dissolved by supercritical liquids and subducted into a deep mantle wedge to depths of 120-300 km in the oceanic subduction zone. This deep metasomatic mantle wedge mixed with the upwelling mantle beneath the Tengchong volcano and partially melted to form the low delta Mg-26 volcanic rocks. (C) 2018 Elsevier Ltd. All rights reserved.
作者机构：
[Mao JingWen; Sun Jia; Yao FoJun] Chinese Acad Geol Sci, Inst Mineral Resources, MLR Key Lab Metallogeny & Mineral Assessment, Beijing 100037, Peoples R China.;[Duan XianZhe] Univ South China, Sch Nucl Resource Engn, Hengyang 421001, Peoples R China.
通讯机构：
[Sun Jia] C;Chinese Acad Geol Sci, Inst Mineral Resources, MLR Key Lab Metallogeny & Mineral Assessment, Beijing 100037, Peoples R China.
通讯机构：
[Tan, Kaixuan] U;Univ South China, Sch Nucl Resources Engn, Hengyang 421001, Hunan, Peoples R China.
关键词：
diffusion;radon;soil;uranium
摘要：
Radon diffusion and transport through different media is a complex process affected by many factors. In this study, the fractal theories and field covering experiments were used to study the fractal characteristics of particle size distribution (PSD) of six kinds of geotechnical materials (e.g., waste rock, sand, laterite, kaolin, mixture of sand and laterite, and mixture of waste rock and laterite) and their effects on radon diffusion. In addition, the radon diffusion coefficient and diffusion length were calculated. Moreover, new formulas for estimating diffusion coefficient and diffusion length functional of fractal dimension d of PSD were proposed. These results demonstrate the following points: (1) the fractal dimension d of the PSD can be used to characterize the property of soils and rocks in the studies of radon diffusion behavior; (2) the diffusion coefficient and diffusion length decrease with increasing fractal dimension of PSD; and (3) the effectiveness of final covers in reducing radon exhalation of uranium tailings impoundments can be evaluated on the basis of the fractal dimension of PSD of materials.
通讯机构：
[Feng, Zhi-Gang] U;Univ South China, Sch Nucl Resource Engn, Hengyang 421001, Peoples R China.
摘要：
Five soil profiles were sampled around a uranium waste rock dump in South China, which included two unpolluted and three potentially uranium-polluted profiles. Through the comparison of the uranium distribution characteristics and the analysis of the uranium chemical forms of these profiles, the following conclusions can be drawn: (1) significant uranium pollution to the surrounding soils was caused by the dump, and the average uranium in these soils, such as the profiles WP1, WP2 and WP3, was 633.6, 9 and 2.7 times more enriched than the background value; (2) the exotic uranium, which was preferentially aggregated in the upper layer of the soils near the pollution source, would be gradually precipitated in the lower layer of the soils away from the pollution source; (3) the input flux of the exotic uranium of each chemical form would be larger in the soils closer to the pollution source.
作者：
Feng, Z. G.*;Zhang, B.;Duan, X. Z.;Chen, R.;Wang, X. L.;...
期刊：
Journal of Residuals Science & Technology,2015年12(SUPPL-1):S159-S163 ISSN：1544-8053
通讯作者：
Feng, Z. G.
作者机构：
[Ma, Q.; Han, S. L.; Zhang, B.; Duan, X. Z.; Chen, R.; Feng, Z. G.; Wang, X. L.] Univ South China, Sch Nucl Resource Engn, Hengyang 421001, Peoples R China.;[Zhang, B.; Chen, R.; Wang, X. L.] Univ South China, Key Discipline Lab Natl Def Biotechnol Uranium &, Hengyang 421001, Peoples R China.
通讯机构：
[Feng, Z. G.] U;Univ South China, Sch Nucl Resource Engn, Hengyang 421001, Peoples R China.
摘要：
Six uranium tailings samples from the shallow depth of two large-scale uranium tailings ponds in South China, which were affected by pedogenesis, were analyzed to determine the occurrence modes of uranium. The results demonstrated that an average of nearly 80% of the uranium in the samples was mobile and potentially mobile, indicating that this type of uranium tailings could significantly threaten their ambient environment when their contents of uranium were relatively high. In this sense, the possibility of the in-situ immobilization of active uranium in the uranium tailings was discussed. The experimental data indicated that the active uranium could be immobilized through its reaction with phosphate, which was theoretically feasible and promising in curbing uranium pollution.
作者机构：
[谢焱石; 尹建文; 谭凯旋; 唐振平; 段先哲; 胡杨; 王正庆; 李春光; 王昭昭; 冯志刚] School of Nuclear Resources Engineering, Hunan Provincial Cooperative Innovation Center for Nuclear Fuel Cycle Technology and Equipment, University of South China, Hengyang;Hunan;421001, China;[谢焱石; 尹建文; 谭凯旋; 唐振平; 段先哲; 胡杨; 王正庆; 李春光; 王昭昭; 冯志刚] Hunan;[谢焱石; 尹建文; 谭凯旋; 唐振平; 段先哲; 胡杨; 王正庆; 李春光; 王昭昭; 冯志刚] 421001, China
通讯机构：
[Tan, K.] S;School of Nuclear Resources Engineering, Hunan Provincial Cooperative Innovation Center for Nuclear Fuel Cycle Technology and Equipment, University of South China, Hengyang, Hunan, China
作者机构：
[Zheng Jian; Hu Yang; Wang Xiaoning; Song Jia; Duan Xianzhe; Yang Bifeng; Feng Zhigang] Univ South China, Sch Nucl Resources Engn, Hengyang 421001, Hunan, Peoples R China.;[Hu Yang] Univ South China, Post Doctoral Res Stn Min Engn, Hengyang 421001, Hunan, Peoples R China.;[Hu Yang] Univ South China, Cooperat Innovat Ctr Nucl Fuel Cycle Technol & Eq, Hengyang 421001, Hunan, Peoples R China.
会议名称：
3rd International Conference on Machinery, Materials Science and Energy Engineering (ICMMSEE)
会议时间：
JUL 18-19, 2015
会议地点：
Wuhan, PEOPLES R CHINA
会议主办单位：
[Duan Xianzhe;Zheng Jian;Wang Xiaoning;Yang Bifeng;Song Jia;Feng Zhigang;Hu Yang] Univ South China, Sch Nucl Resources Engn, Hengyang 421001, Hunan, Peoples R China.^[Hu Yang] Univ South China, Post Doctoral Res Stn Min Engn, Hengyang 421001, Hunan, Peoples R China.^[Hu Yang] Univ South China, Cooperat Innovat Ctr Nucl Fuel Cycle Technol & Eq, Hengyang 421001, Hunan, Peoples R China.
关键词：
Sandstone-type uranium deposit;Chemical speciation of uranium;Sequential chemical extraction;In-situ Leaching
摘要：
Sequential chemical extraction procedure was modified from Tessier process and demonstrates its application to sandstone uranium exploration. Use it to study uranium speciation with six different samples from in-situ leaching sandstone-type uranium deposits. The chemical speciation of uranium in samples was classified into six speciation: the exchangeable ion, carbonates bound, sulfide-organic matter speciation bound, amorphous Fe-Mn oxides bound, sparry Fe-Mn oxides bound and the residual state. Through the research, the uranium distribution characteristics were significantly different whether they were in different samples or in the same sample. Therefore, the research on chemical speciation of uranium Deposit before the production is essential to reasonable evaluation of Deposit and can guide the technology of in-situ leaching uranium Deposit. It also can rich the mineralization mechanism of sandstone-type uranium Deposit.
