| YANG Baoju,ZENG Zhigang,WANG Xiaoyuan,YIN Xuebo,CHEN Shuai. 2014. Pourbaix diagrams to decipher precipitation conditions of Si-Fe- Mn-oxyhydroxides at the PACMANUS hydrothermal field. Acta Oceanologica Sinica, 33(12):58－66 |
| Pourbaix diagrams to decipher precipitation conditions of Si-Fe- Mn-oxyhydroxides at the PACMANUS hydrothermal field |
| 布拜图对PACMANUS热液区Si-Fe-Mn-羟基氧化物沉淀条件的指示 |
| Received:July 17, 2013 Revised:March 26, 2014 |
| DOI：10.1007/s13131-014-0572-9 |
| Key words:Si-Fe-Mn-oxyhydroxides PACMANUS hydrothermal field Pourbaix diagrams |
| 中文关键词: Si-Fe-Mn-羟基氧化物 PACMANUS热液区 布拜图 |
| 基金项目:The National Key Basic Research Program of China under contract Nos 2013CB429700; the National Special Fund for the 12th Five Year Plan of COMRA under contract Nos DY125-12-R-02 and DY125-12-R-05; the National Natural Science Foundation of China under contract Nos 41325021, 40830849, 40976027 and 41476044; the Shandong Province Natural Science Foundation of China for Distinguished Young Scholars under contract Nos JQ200913; the Strategic Priority Research Program of the Chinese Academy of Sciences under contract No. XDA11030302; the CAS/SAFEA International Partnership Program for Creative Research Teams. |
| Author Name | Affiliation | E-mail | | YANG Baoju | Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
University of Chinese Academy of Sciences, Beijing 100049, China | | | ZENG Zhigang | Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China | zgzeng@qdio.ac.cn | | WANG Xiaoyuan | Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China | | | YIN Xuebo | Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China | | | CHEN Shuai | Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China | |
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| Abstract: |
| Utilizing Si, Fe and Mn concentrations within the end-member PACMANUS hydrothermal fluid, Si-Fe-Mn- H2O Pourbaix diagrams were constructed at 300℃ and 25℃. The Pourbaix diagrams show that the main Si, Fe and Mn oxides species precipitating from the hydrothermal fluid were SiO2, Fe(OH)3, Fe3(OH)8, Mn3O4, and Mn2O3 at 25℃. During mixing of hydrothermal fluid with seawater, SiO2 precipitated earlier than Fe- Mn-oxyhydroxides because of the lower stability boundary. Then Fe(OH)2 precipitated first, followed by Fe3(OH)8 and Fe(OH)3, and last, small amounts of Mn3O4 and Mn2O3 precipitated. Fe(OH)3 was readily deposited in alkaline solution with little influence by Eh. There were many Si-Fe-Mn-concentric particles in the polished sections of the massive precipitates collected from PACMANUS. In the concentric nucleus and ellipsoid, Si oxides precipitated first before the hydrothermal fluid had mixed with seawater. In the concentric nucleus, after the precipitation of Si oxides, the increase of pH and Eh promoted the precipitation of Mn oxides around the Si oxides. In the large ellipsoid, the precipitation of Fe was divided into two periods. In the early period, increase of pH value of hydrothermal fluid produced by low-temperature convection and an input of a small volume of seawater promoted a small amount of Fe(OH)3 to precipitate in the Si-rich core. In the late period, after complete mixing with seawater and the resultant fluid was close to neutral or slightly alkaline in pH, Fe(OH)3 was easily precipitated from the solution and distributed around the Si-rich core. |
| 中文摘要: |
| 利用PACMANUS热液区热液流体端元组分的Si、Fe、Mn含量,绘制了300℃和25℃的Si-Fe-Mn-H2O系统布拜图.布拜图显示当温度降低到25℃时,从热液流体中形成的Si、Fe、Mn羟基氧化物种类主要为SiO2、Fe(OH)3、Fe3(OH)8、Mn3O4、Mn2O3.在热液流体与海水混合过程中,由于SiO2的稳定区边界较低,因此SiO2会在Fe-Mn羟基氧化物形成之前沉淀.然后Fe(OH)2 沉淀,Fe3(OH)8和Fe(OH)3 随后沉淀,Mn3O4 和Mn2O3最后沉淀.光薄片在显微镜下可见大量的Si-Fe-Mn-同心环和椭球体.在这两种结构中,Si氧化物都形成于热液流体与海水混合之前.在同心环中,Si氧化物沉淀之后,随着热液流体与海水的混合,逐渐升高的pH值和Eh值促使Mn羟基氧化物从热液流体中沉淀,围绕Si质核分布.在椭球体中,Fe羟基氧化物的沉淀分为两个阶段.早期热液流体与海水低温对流及与少量海水混合使得热液流体酸性逐渐减弱,促使少量Fe(OH)3 沉淀并分布于Si质核周围.后期,随着热液流体与海水的混合程度增大,热液流体逐渐变为中性及偏碱性的环境,该环境有利于大量的Fe(OH)3从热液流体中沉淀并分布于椭球体的外围. |
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