| BU Wenrui,SHI Xuefa,PENG Jiantang,LIU Jihua,Zhang Mingjie,QI Liang. 2008. Low-temperature alteration of oceanic island basalts and their contribution to transition metal circulation of the ocean. Acta Oceanologica Sinica, (2):35－54 |
| Low-temperature alteration of oceanic island basalts and their contribution to transition metal circulation of the ocean |
| Low-temperature alteration of oceanic island basalts and their contribution to transition metal circulation of the ocean |
| Received:February 27, 2006 Revised:January 26, 2007 |
| DOI： |
| Key words:oceanic island basalts(OIB) low-temperature alteration ocean metal circulation theoretical calculation cobalt-rich ferromanganese crusts |
| 中文关键词: oceanic island basalts(OIB) low-temperature alteration ocean metal circulation theoretical calculation cobalt-rich ferromanganese crusts |
| 基金项目:The National Natural Science Foundation of China (NSFC) under contract No. 40706028;the China Oceanic Mineral Resources Re-search and Development Association (COMRA) under contract No. DYXM115-01-2-01. |
| Author Name | Affiliation | E-mail | | BU Wenrui | Key Laboratory of Marine Sedimentology & Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China | buwenrui@rio.org.cn | | SHI Xuefa | Key Laboratory of Marine Sedimentology & Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China | | | PENG Jiantang | Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China | | | LIU Jihua | Key Laboratory of Marine Sedimentology & Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China | | | Zhang Mingjie | College of Earth and Environmental Science, Lanzhou University, Lanzhou 730000, China | | | QI Liang | Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, 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 ferromanganese 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 Al2O3, Fe2O3, MnO, K2O and P2O5 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 basalts 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. |
| 中文摘要: |
| The major elements, rare earth elements (REE) and trace elements of four basalt samples from central and western Pacific ferromanganese 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 Al2O3, Fe2O3, MnO, K2O and P2O5 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 basalts 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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