| 摘要: |
| 用碱熔法新测得Jade热液区7件海底块状硫化物样品的锇含量及其同位素组成, 187Os/186Os比值在2.205—6.462之间, 均值为4.314, 高于地幔端员, 而低于海洋沉积物和海水端员, 表明该区块状硫化物中锇是深部来源锇与海水和/或沉积物混合的产物。结合该区块状硫化物样品的REE、硫和铅同位素组成特征, 进一步揭示出海水、长英质火山岩、沉积物和深部地幔源是形成Jade区块状硫化物的物源。
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| 关键词: 锇同位素,海底块状硫化物,Jade热液区,冲绳海槽 |
| DOI：10.11693/hyhz200304007007 |
| 分类号: |
| 基金项目:国家重点基础研究发展规划项目,G2000046701号和国家自然科学基金资助项目,40176020号 |
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| OS ISOTOPIC COMPOSITIONS OF SEAFLOOR MASSIVE SULFIDES FROM THE JADE HYDROTHERMAL FIELD IN THE OKINAWA TROUGH |
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Zeng Zhi-Gang1, Zhai Shi-Kui2, Du An-Dao3
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1.Institute of Oceanology, The Chinese Academy of Sciences;2.Ocean University of China;3.Institute of Rock and Mineral Analysis, Chinese Academy of Geological Sciences
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| Abstract: |
| In the Okinawa Trough, the rare earth elements, sulfur and lead isotopic compositions of seafloor massive sulfides from the Jade hydrothermal have been studied in order to understand their sources. Although we know the source of rare earth elements, sulfur and lead in the sea floor massive sulfides, we do not know the sources of the major metal materials of forming seafloor massive sulfides, for example, iron, copper, zinc,etc.; it is still a disputing question ont he material sources of forming seafloor massive sulfides. Due to the material sources of forming seafloor massive sulfides from the Jade hydrothermal field is a key question for understanding the formation mechanism of seafloor massive sulfides and the evolution of seafloor hydrothermal activity in the Okinawa Trough. This paper will report the analytical results of osmium isotopic compositions of seafloor massive sulfides from the Jade hydrothermal field, study the characteristics of osmium isotopic compositions of seafloor massive sulfides, and discuss the material sources of hydrothermal ore-forming in the Jade hydrothermal field. For measuring the osmium isotopic compositions of seafloor massive sulfides from the Jade hydrothermal field, the whole rock samples of massive sulfides were rubbed in an agate mortar, adding the suitable Na2O2 and NaOH to the powder samples of 0.5—1g, then the samples were heated to 700℃ for melting, using the hot-water to distill the melting samples, adding the acetone to the solution of 4/5 volume for extracting the rhenium, adding CrO3 and H2SO4 to the solution of 1/5 volume for acidifying. The OsO4 from the solution were absorbed by HBr, then the rhenium contents and osmium isotopic compositions of samples were measured by the MAT-262 mass spectrograph.
New data on the osmium isotopic compositions, the rhenium and osmium contents of seven seafloor massive sulfide samples from the Jade hydrothermal field have been obtained. The rhenium content range of massive sulfide samples is from3.505×10-9 to 154.900×10-9, with a mean of 61.049×10-9, the osmium content range of massive sulfide samples is from 0.279×10-9 to 43.930×10-9, with a mean of 7.739×10-9, the rhenium and osmium contents of seafloor massive sulfides has a large variable range, and the 187Os/186Os ratios of massive sulfide samples vary from 2.205 to mean of 4.790. These ratios are lower than the mantle-source endmembers, and higher than modern seawater and marine sediment endmembers. The characteristic of Os isotopic compositions is probably the result of mixing of seawater and/or sediment with mantle-source osmium. Unfortunately, we do not know the osmium isotopic compositions of felsic volcanic rocks, marine sediments and continental crust endmembers in the Okinawa Trough, so it is difficult to evaluate the contributing ratio of material for forming seafloor massive sulfides of the Jade hydrothermal field from different material endmembers. Combining the study of rare earth elements, sulfur and lead isotope of massive sulfides from the Jade hydrothermal field show that seawater, felsic volcanic rocks, marine sediments and mantle-sources endmembers may become the sources of forming the massive sulfides. In the future, the iron and copper isotopic compositions of seafloor massive sulfides from the Jade hydrothermal field inthe Okinawa Trough should be measured for understanding the material sources of forming massive sulfides.
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| Key words: Osmium isotope, Seafloor massive sulfide, Jade hydrothermal field, Okinawa Trough |
