| Low-temperature alteration of oceanic island basalts and their contribution to transition metal circulation of the ocean |
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| 作者姓名： | BU Wenrui SHI Xuef PENG Jiantang LIU Jihu Zhang Mingjie QI Liang |
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| 作者单位： | [1]Key Laboratory of Marine Sedimentology ＆ Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China [2]Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China [3]College of Earth and Environmental Science, Lanzhou University, Lanzhou 730000, China |
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| 基金项目： | 国家自然科学基金，The China Oceanic Mineral Resources Research and Development Association (COMRA) |
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| 摘 要： | The major elements, rare earth elements （REE） and trace elements of four basalt samples from central and western Pacific ferro- manganese crust provinces have been analyzed using chemical methods and ICP - MS, respectively. The results indicate that the samples have been extensively altered and that the contents of their major elements have changed significantly. However, the similarity of REE partition patterns and trace element contents of basalt samples to those of fresh oceanic island basalts （OIB） indicate that the basalt samples originated as OIB. Because of low-temperature alteration, the contents of A1203 , Fe203 , MnO, K20 and P205 increased, while MgO and FeO decreased. Active components, such as magnesium and iron, were leached from OIB resulting in the relative enrichment of SiO2. The leaching of active components can cause the relative enrichment of REE, while the precipitation of LREE-rich ferromanganese oxides in vesicles and fissures not only causes an increase of REE contents, but also induces ＂fractionation＂ of LREE and HREE. Based on the enrichment mechanism of REE contents, the theoretical quantities of precipitated ferromanganese oxides and the depleted quantities of active components are calculated ： the depleted quantities of active components for the unit mass of fresh basalts vary in the range of 0.15 ～ 0. 657, and the precipitated quantities of ferromanganese oxides for the unit mass of fresh basahs vary in the range of 0. 006 ～ 0. 042. Of the major elements, the two most depleted are iron, and magnesium, with 18.28% ～ 70.95% of iron and 44.50% ～ 93.94% of magnesium in the fresh basalts was leached out. Theoretical calculation and geochemistry results both indicate that low-temperature alteration of basalts can supply abundant amount of metals to seawater, and may play an important role in ocean metal circulation.
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| 关 键 词： | 海岛 玄武岩 理论计算 低温变化 海洋金属循环 |
| 收稿时间： | 2006/2/27 0:00:00 |
| 修稿时间： | 2007/1/26 0:00:00 |
Low-temperature alteration of oceanic island basalts and their contribution to transition metal circulation of the ocean |
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| BU Wenrui,SHI Xuef,PENG Jiantang,LIU Jihu,Zhang Mingjie,QI Liang.Low-temperature alteration of oceanic island basalts and their contribution to transition metal circulation of the ocean[J].Acta Oceanologica Sinica,2008,27(2):35-54. |
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| Authors: | BU Wenrui SHI Xuef PENG Jiantang LIU Jihu Zhang Mingjie and QI Liang |
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| Institution: | 1.Key Laboratory of Marine Sedimentology & Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China2.Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China3.College of Earth and Environmental Science, Lanzhou University, Lanzhou 730000, China |
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| Abstract: | The major elements,rare earth elements (REE) and trace elements of four basalt samples from central and western Pacific ferro-manganese crust provinces have been analyzed using chemical methods and ICP - MS,respectively.The results indicate that the samples have been extensively altered and that the contents of their major elements have changed significantly.However,the simi-larity of REE partition patterns and trace element contents of basalt samples to those of fresh oceanic island basalts (OIB) indicate that the basalt samples originated as OIB.Because of low-temperature alteration,the contents of Al2O3 ,Fe2O3 ,MnO,K2O and P2O5 increased,while MgO and FeO decreased.Active components,such as magnesium and iron,were leached from OIB resul-ting in the relative enrichment of SiO2.The leaching of active components can cause the relative enrichment of REE,while the precipitation of LREE-rich ferromanganese oxides in vesicles and fissures not only causes an increase of REE contents,but also induces "fractionation" of LREE and HREE.Based on the enrichment mechanism of REE contents,the theoretical quantities of precipitated ferromanganese oxides and the depleted quantities of active components are calculated :the depleted quantities of ac-tive components for the unit mass of fresh basalts vary in the range of 0.15～0.657,and the precipitated quantities of ferromanga-nese oxides for the unit mass of fresh basahs vary in the range of 0.006～0.042.Of the major elements,the two most depleted are iron,and magnesium,with 18.28%～70.95% of iron and 44.50%～93.94% of magnesium in the fresh basalts was leached out.Theoretical calculation and geochemistry results beth indicate that low-temperature alteration of basalts can supply abundant amount of metals to seawater,and may play an important role in ocean metal circulation. |
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| Keywords: | oceanic island basalts (OIB) low-temperature alteration ocean metal circulation theoretical calculation cobalt-rich ferromanganese crusts |
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