| LI Zhenggang,CHU Fengyou,JIN Lu,LI Xiaohu,DONG Yanhui,CHEN Ling,ZHU Jihao. 2016. Major and trace element composition of surface sediments from the Southwest Indian Ridge: evidence for the incorporation of a hydrothermal component. Acta Oceanologica Sinica, 35(2):101－108 |
| Major and trace element composition of surface sediments from the Southwest Indian Ridge: evidence for the incorporation of a hydrothermal component |
| 西南印度洋中脊表层沉积物中存在热液组分的地球化学证据 |
| Received:December 05, 2014 Revised:March 31, 2015 |
| DOI：10.1007/s13131-015-0678-8 |
| Key words:deep-sea sediments hydrothermal component diffuse fluid eolian dust Southwest Indian Ridge |
| 中文关键词: 深海沉积物 热液组分 低温弥散流 风尘砂 西南印度洋中脊 |
| 基金项目: |
| Author Name | Affiliation | E-mail | | LI Zhenggang | Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration (SOA), Hangzhou 310012, China
Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China | | | CHU Fengyou | Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration (SOA), Hangzhou 310012, China
Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China | chu@sio.org.cn | | JIN Lu | Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration (SOA), Hangzhou 310012, China
Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China | | | LI Xiaohu | Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration (SOA), Hangzhou 310012, China | | | DONG Yanhui | Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration (SOA), Hangzhou 310012, China | | | CHEN Ling | Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration (SOA), Hangzhou 310012, China
Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China | | | ZHU Jihao | Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration (SOA), Hangzhou 310012, China | |
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| Abstract: |
| Hydrothermal materials in deep-sea sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Major, trace and rare earth element (REE) data for surface sediments collected from the ultraslow spreading Southwest Indian Ridge are presented to examine the existence of hydrothermal component. Biogenic carbonate oozes dominate all the sediment samples, with CaO content varying from 85.5% to 89.9% on a volatile-free basis. The leaching residue of bulk sediments by ~5% HCl is compositionally comparable to the Upper Continental Crust (UCC) in SiO2, Al2O3, CaO, MgO, alkali elements (Rb, Cs) and high field strength elements (Nb, Ta, Zr, Hf, Ti). These detritus-hosted elements are inferred to be prominently derived from the Australian continent by means of eolian dust, while the contribution of local volcaniclastics is insignificant. In addition, the residual fraction shows a clear enrichment in Fe, Mn, and Ba compared with the UCC. Combining the positive Eu anomaly of residual fraction which is opposed to the UCC but the characteristic of hydrothermal fluids and associated precipitates occurred at mid-ocean ridges, the incorporation of localized hydrothermal component can be constrained. REE mixing calculations indicate that more than half REE within the residual fraction (~55%-60%) are derived from a hydrothermal component, which is inferred to be resulted from a diffuse fluid mineralization. The low-temperature diffuse flow may be widely distributed along the slow-ultraslow spreading ridges where crustal faults and fissures abound, and probably have a great mineralization potential. |
| 中文摘要: |
| 深海沉积物中的热液组分能够记录附近的热液活动。本研究对超慢速扩张的西南印度洋中脊表层沉积物进行了主量、微量以及稀土元素分析,检测沉积物中是否有热液组分的存在。表层沉积物均以生物碳酸盐软泥为主,CaO的含量介于85.5%至89.9%之间(去除挥发份后)。经~5%稀盐酸去除沉积物中生物成因的碳酸钙后,其残留物与上地壳具有近似的SiO2、Al2O3、CaO、MgO、碱金属(Rb和Cs)以及高场强元素(Nb、Ta、Zr、Hf和Ti)组成。这些“岩屑元素”并非来源于附近的火山碎屑,而主要来自澳大利亚大陆的风尘砂。此外,该残留物与上地壳相比具有显著的正Eu异常,这与陆源碎屑正好相反。而正Eu异常是海底热液流体以及热液沉淀物的典型特征,再加上残留物具有富集Fe、Mn和Ba的特征,推测沉积物中有热液组分的加入。二元混合计算结果显示残留物中热液组分的贡献超过50%。由于沉积物中并没有观察到热液沉淀物互层的现象,排除了热液组分来自附近垮塌烟囱体的可能,最有可能的解释是低温弥散流的矿化。对于断层和裂隙较为发育的慢速或超慢速扩张脊(如西南印度洋中脊),广泛存在的低温弥散流在洋壳浅部的矿化潜力有可能被严重低估。 |
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