海洋地质与环境重点实验室知识库

本文选择马里亚纳岛弧北部 NW Eifuku 热液区的一块火山岩及其中的黄铁矿作为研究对象，对样品进行了详细的岩相学、矿相学及矿物学和地球化学研究，分析岩石及其中黄铁矿的元素组成特征，讨论不同类型的黄铁矿其主要组成元素的变化及造岩矿物、微生物作用与硫化物之间的相互影响，通过分析黄铁矿的 S同位素组成，揭示了该地区岩石中黄铁矿的 S 来源。
研究区位于马里亚纳岛弧北部的 NW Eifuku 热液区（21.49° N, 144.04° E），处于一个构造活跃的地带。对该热液区中岩石样品进行了全岩主微量分析，确定岩石为钙碱性玄武安山岩，形成于造山带环境，斑晶矿物主要为橄榄石、斜长石和单斜辉石。对这三种斑晶矿物进行电子探针测试，结果显示，四块岩石样品的斑晶成分和种类存在差异，结合全岩主微量元素含量特征，推测该热液区岩石的岩浆源区受到了俯冲组分的影响，且存在一定程度的岩浆演化。
对岩石中的黄铁矿进行了电子探针测试、原位 S 同位素测试，探讨了黄铁矿的地球化学特征、物质来源和微生物成矿。结果显示，其中一件岩石样品包含四种类型的黄铁矿，分别为蚀变斑晶中黄铁矿、斑晶裂隙中黄铁矿、基质中黄铁矿、气孔中黄铁矿。后三种黄铁矿的晶形为自形-半自形，是热液活动早期的产物，蚀变斑晶中黄铁矿的晶形为他形和胶状，结合黄铁矿的元素组成特征，S/Fe 比值存在由低到高的变化，指示黄铁矿的形成温度由高到低，同时蚀变斑晶中黄铁矿Co/Ni 值减小，这些都表明后三者为早期生成，蚀变斑晶中黄铁矿为晚期低温且相对开放的条件下形成。
除基质中黄铁矿外，三类黄铁矿的 δ34S 值为负值（-6.58‰~-19.60‰），与气孔中和斑晶裂隙中黄铁矿的 S 同位素值（-6.58‰至-9.37‰）相比，蚀变斑晶中黄铁矿的 δ34S 值（-9.01‰至-19.60‰）更偏负，表明其形成环境受到了其他因素的影响，沉淀蚀变斑晶矿物中黄铁矿的低温流体相对亏损 34S。
海底热液系统中存在很多耐高温的微生物群落，它们可以通过四种方式（直接富集、改变环境条件、产生有机质、新陈代谢作用）对 Cd、Zn、Co、Ni 等金属元素进行富集。在氧化还原过程中，微生物可以利用电子迁移释放的能量进行自身生命活动，并会对已经形成的金属矿物进行溶蚀作用，导致矿物边缘存在金属氧化层。黄铁矿的 δ34S 值均为负值且较小，部分自形黄铁矿有铁氧化层边缘，均表明黄铁矿在形成过程中可能受到了微生物作用的影响，导致后期蚀变橄榄石中黄铁矿的 Co、Ni 元素的含量明显高于其他类型黄铁矿，且蚀变橄榄石对黄铁矿的元素含量影响相对较小。综合上述特征，推测在热液活动后期，橄榄石斑晶受到热液侵蚀后发生蚀变，其部分 Fe 元素进入到热液中或被微生物利用，黄铁矿逐渐从热液流体中沉淀析出，形成于蚀变岩石内。

In this paper, the volcanic rock and its pyrite near NW Eifuku hydrothermal vent in the Mariana Arc are selected as the research object. Detailed petrographic, mineralogical and geochemical studies are carried out on the sample to analyze the elemental composition characteristics of the rock and its pyrite. We discuss the changes of the main components of different types of pyrite and the interaction between rock-forming minerals, microbial action and sulfide. The S isotope composition of pyrite is analyzed to reveal the S source of pyrite in the rock in this area.

The study area is located in the NW Eifuku hydrothermal field of the northern Mariana Arc (21.49° N, 144.04° E), which is in an active tectonic zone. The whole rock major and trace analysis of the rock samples confirmed that the rock is calc-alkaline basaltic andesite formed in the orogenic belt environment, and the phenocrysts are mainly olivine, plagioclase and clinopyroxene. The results of the electron probe test on the phenocryst of three silicate minerals show that there are differences in the composition and types of the phenocryst of the four rock samples. Combined with the content characteristics of major and trace elements in the whole rock, it is inferred that the magmatic source region of the rocks in the hydrothermal area is affected by subduction components, and there is a certain degree of magmatic evolution.

Electron microprobe analytical data and in situ S-isotope data of pyrite in rocks investigate the geochemical characteristic, sulfur source, and microbial mineralization of pyrite. The results show that one of the rock samples contains four types of pyrite: pyrite located in the altered phenocryst, pyrite located in the phenocryst fissure, pyrite located in the matrix, and pyrite located in the air bubbles. The crystal form of the last three types of pyrite are euhedral and subhedral, which are the product of the early hydrothermal activity. The crystal form of pyrite located in the altered phenocryst is xenomorphic and colloidal. Combined with the characteristics of the elemental composition of pyrite, the S/Fe ratio changes from low to high, indicating that the formation temperature of pyrite is from high to low. At the same time, the Co/Ni ratio of pyrite located in the altered phenocryst is reduced. All these indicate that the latter three types of pyrite are formed in the early stage, and the pyrite located in the altered phenocryst is formed in the late stage under low temperature and relatively open condition.

Except for pyrite in matrix, the δ³⁴S values of the three types of pyrite are negative (-6.58‰ to -19.60‰). The δ³⁴S values of pyrite located in the altered phenocryst range from -9.01‰ to -19.60‰. Compared with the S isotopic compositions of the other two types of pyrite, the δ³⁴S value of most of pyrite located in the altered phenocrysts is more negative, indicating that the environment of its formation has been influenced by other factors Influence and the low-temperature fluid for forming pyrite located in the altered phenocrysts is relatively depleted in ³⁴S.

There are many high-temperature resistant microbial communities in the submarine hydrothermal system, which can enrich Cd, Zn, Co, Ni and other metal elements through four ways (direct enrichment, changing environmental conditions, the process of organic matter production, and metabolic action). During the redox process, microorganisms can utilize the energy released by electron migration for their own life activities, and they will dissolve the metal minerals that have been formed, resulting in the presence of metal oxide layers at the edges of the minerals. The δ³⁴S values of pyrite are all negative and small, and some of the euhedral pyrite has the edge of iron oxide layer, all of which indicate that pyrite may have been affected by microbial action during the formation process, resulting in the content of Co and Ni elements of pyrite in the later altered peridotite is significantly higher than that of other types of pyrite, and the effect of altered peridotite on the elemental content of pyrite is relatively small. Combining the above features, it is speculated that in the late stage of hydrothermal activity, the olivine phenocryst were eroded by the hydrothermal fluid and then altered, and some of its Fe elements entered into the hydrothermal fluid or were utilized by microorganisms, and pyrite was gradually precipitated out from the hydrothermal fluid and formed within the altered rocks.

第1章 绪论 

1.1 选题目的及意义   

1.2 国内外研究现状   

1.2.1 现代海底热液硫化物调查研究概况 

1.2.2 热液硫化物的物质来源    

1.2.3 热液区生物对硫化物形成的影响    

1.2.4 马里亚纳海槽与岛弧系统的热液硫化物调查研究简史 

1.3 拟解决的科学问题

1.4 主要研究内容

1.5 技术路线

1.6 完成工作量   

第2章 马里亚纳海槽与岛弧地质背景    

2.1 地形地貌

2.2 构造环境

2.3 马里亚纳海槽的岩石分布及特征

2.4 马里亚纳岛弧与NW Eifuku热液区   

第3章 样品及分析方法    

3.1 样品来源

3.2 样品的分析方法   

3.2.1 前处理 

3.2.2 镜下观测    

3.2.3 全岩主微量元素分析 

3.2.4 扫描电镜分析    

3.2.5 硅酸盐矿物和黄铁矿的电子探针分析    

3.2.6 黄铁矿的S同位素分析    

第4章 岩石学特征    

4.1 样品手标本描述   

4.2 岩相学特征   

4.3 地球化学特征

4.3.1 全岩主量元素组成特征    

4.3.2 全岩微量元素组成特征    

4.3.3 主要造岩矿物的元素组成特征 

4.4 本章小结

第5章 岩石中硫化物的矿物与地球化学特征 

5.1 矿物学特征   

5.2 黄铁矿矿物成分分析   

5.3 黄铁矿的S同位素组成特征

5.4 本章小结

第6章 热液黄铁矿成因分析    

6.1 物质来源

6.2 形成过程

6.3 微生物对黄铁矿的影响

6.4 本章小结

第7章 结论与展望

参考文献      

致  谢   

作者简历及攻读学位期间发表的学术论文与其他相关学术成果