西南印度洋超慢速扩张洋脊49.2°E—50.5°E热液区热液沉积物的地球化学特征及成因

doi:10.3964/j.issn.1000-0593(2023)09-2868-08

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摘要：分析了西南印度洋超慢速扩张洋脊49.2°E—50.5°E热液区热液沉积物样品的矿物组成和元素地球化学特征，结果显示研究区热液沉积物矿物组成以黄铁矿和黄铜矿为主，还含有少量闪锌矿等，而硅烟囱和残留氧化物分别主要由无定形硅和碳酸钙、铁氢氧化物（如针铁矿）等矿物组成，由热液沉积物到硅烟囱，再到残留氧化物过渡过程中，矿物组成中硫化物含量以及矿物结晶程度的降低，指示了成矿温度逐渐降低的趋势。同时，通过XRF、ICP-AES等手段对热液沉积物的主微量元素分析，主微量地球化学特征指示海水的贡献逐步增大，而热液对其影响逐步减小，形成环境也逐步从热液羽状流环境向海相水成的低温氧化环境转变。在稀土元素分析中，热液沉积物中稀土元素总体含量较高，∑REE（26.37～32.86）×10^-6；残留氧化物中稀土元素含量次之，∑REE（5.58～30.43）×10^-6；硅烟囱中稀土元素含量较低∑REE（0.92～6.96）×10^-6。研究区样品均表现出轻稀土元素富集、重稀土元素亏损的特征，δ_Ce值变化范围为0.34～1.00，具有Ce负异常特征；δ_Eu值变化范围为0.87～4.24，具有Eu正异常特征，指示样品继承热液流体的部分地球化学特征的同时，又受到了海水的明显影响，稀土来源具有多样性的特征。综合分析表明，研究区由于受制于较弱的热液活动，以中低温为主的成矿环境，成矿流体主要起源于海水，因此成矿过程受海水混合作用影响较大。

关键词：热液沉积物；主量元素；微量元素；地球化学特征；成因；西南印度洋中脊

Abstract：The hydrothermal sediment samples from the 49.2°E—50.5°E hydrothermal fields of the Southwest Indian Ocean ultra-slow spreading ridge were analyzed for the mineral compositions and elemental geochemical characteristics. Moreover, the results show that the mineral compositions of the hydrothermal sediments in the study area are mainly pyrite and chalcopyrite, also possessed slightly sphalerite. Meanwhile，the silicon chimneys and residual oxides are composed predominantly of amorphous silicon, calcium carbonate, and iron hydroxides (such as goethite). The transition trend of the mineral assembles from the hydrothermal sediments to the residual oxides indicates that the changing process of its ore-forming temperature decreasing gradually. Furthermore, the main and trace element geochemical characteristics of the hydrothermal sediments were analyzed by XRF and ICP-AES. Geochemical characteristics of the main and trace elements show that the contribution of seawater increases gradually and reduces the influence of hydrothermal fluid. The formation environment also changes gradually from the hydrothermal plume flow condition to the low temperature conditions of the marine aquatic. In the analysis of rare earth elements (REE), the hydrothermal sediment samples contained the highest contents of rare earth elements [∑REE: （26.37～32.86）×10^-6], residual oxides samples contained the second highest contents of rare earth elements [∑REE: （5.58～30.43）×10^-6], and silicon chimneys samples contained the lowest contents of rare earth elements [∑REE: （0.92～6.96）×10^-6]. Besides, all of the samples enrich the light rare earth elements (LREE) and deplete the heavy rare earth elements, with Ce negative anomaly (δCe: 0.34～1.00) and Eu positive anomaly (δEu: 0.87～4.24). Geochemical characteristics of rare earth elements suggest that the samples not only inherited part of the geochemical characteristics of hydrothermal fluid but were also affected obviously by seawater, and the source of REE in the hydrothermal sediments has diversity characteristics. Comprehensive analysis shows that the metallogenic environment of the study area is predominantly in the low temperature due to limited weak hydrothermal activity, and the ore-forming fluid mainly originated in seawater. Therefore, the metallogenic process is greatly influenced by the ambient seawater's mixing action.

Key words：Hydrothermal sediments; The main element; The trace element; Geochemical characteristics; Genesis; Southwest indian ocean ridge

收稿日期: 2022-05-08 修订日期: 2023-02-06

中图分类号:

P59

基金资助: 国家自然科学基金项目(41503036，41602092)，中国海洋发展研究会研究项目(CAMAZD201909)，自然资源部海洋环境探测技术与应用重点实验室自主设立课题项目(MESTA-2021-D005)，广东省海洋经济发展（海洋六大产业）专项资金项目（GDNRC[2022]51）资助

通讯作者: 黄毅，杨帆 E-mail: huangy@scs.mnr.gov.cn；yangfan@scs.mnr.gov.cn

作者简介: 王琰，1988年生，国家海洋局南海规划与环境研究院博士及高级工程师 e-mail: we85289786@163.com

引用本文:

王琰，黄毅，杨帆，吴仲玮，关瑶，薛飞. 西南印度洋超慢速扩张洋脊49.2°E—50.5°E热液区热液沉积物的地球化学特征及成因[J]. 光谱学与光谱分析, 2023, 43(09): 2868-2875.
WANG Yan, HUANG Yi, YANG Fan, WU Zhong-wei, GUAN Yao, XUE Fei. The Origin and Geochemical Characteristics of the Hydrothermal Sediments From the 49.2°E—50.5°E Hydrothermal Fields of the Southwest Indian Ocean Ultra-Slow Spreading Ridge. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2023, 43(09): 2868-2875.

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