In Situ Analysis of Element Geochemistry in Submarine Basalt in Hydrothermal Areas from Ultraslow Spreading Southwest Indian Ridge
WANG Yan1, 2, 5, SUN Xiao-ming1，3，4*, XU Li1, 3*, LIANG Ye-heng1, 2, WU Zhong-wei1，3, FU Yu1, 4, HUANG Yi1,3
1. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510275, China 2. Key Laboratory of Marine Mineral Resources, Ministry of Land and Resources,Guangzhou 510075, China 3. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510006, China 4. School of Earth Science and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China 5. South China Sea Marine Engineering and Environmont Institute, State Oceanic Administration, Guangzhou 510200, China
Abstract：In this study, we analyze element geochemistry of submarine basalt in situ, which is sampled in hydrothermal areas from ultraslow spreading Southwest Indian Ridge, including the fresh basalt rocks (B19-9, B15-13) and altered basalt (B5-2). And we can confirm that altered mineral in B5-2 is celadonite by microscope and Raman Spectrum. Furthermore, amygdaloidal celadonites are analyzed by electron microprobe (EPMA) and EDS-line scanning. The results show that K-contents decrease and Na-contents increase from the core to the edge in thesealtered minerals, indicating the transition from celadonite to saponite. Celadonite is an altered minerals, forming in low temperature(<50 ℃) and oxidizing condition, while saponite form in low water/rock and more reducing condition. As a result, the transition from celadonite to saponite suggests environmentchange from oxidizing to reducing condition. Using the result of EPMA as internal standard, we can analyze rare earth elements (REE) in altered mineral in situ. Most of result show positive Eu anomaly (δEu), indicating hydrothermal fluid transform from oxidizing to reducing, and reducing fluid rework on the early altered minerals. Comparison with REE in matrix feldspar both in altered and unaltered zoning, we find that reducing fluid can leach REE from the matrix feldspar, leading to lower total REE concentrations and positive Eu anomaly. So leaching process play an important role in hydrothermal system.
Key words：SWIR;Submarine basalt;Altered mineral;Low temperature alteration;LA-ICPMAS;element geochemistry
王 琰1，2，5，孙晓明1，3，4*，徐 莉1, 3*，梁业恒1，2，吴仲玮1，3，付 宇1, 4，黄 毅1, 3 . 西南印度洋中脊热液区海底玄武岩元素地球化学原位分析 [J]. 光谱学与光谱分析, 2015, 35(03): 796-802.
WANG Yan1, 2, 5, SUN Xiao-ming1，3，4*, XU Li1, 3*, LIANG Ye-heng1, 2, WU Zhong-wei1，3, FU Yu1, 4, HUANG Yi1,3 . In Situ Analysis of Element Geochemistry in Submarine Basalt in Hydrothermal Areas from Ultraslow Spreading Southwest Indian Ridge. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2015, 35(03): 796-802.
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